/*  sexp.c -- standalone sexp library implementation          */
/*  Copyright (c) 2009-2011 Alex Shinn.  All rights reserved. */
/*  BSD-style license: http://synthcode.com/license.txt       */

#include "chibi/sexp.h"

/* optional huffman-compressed immediate symbols */
struct sexp_huff_entry {
  unsigned char len;
  unsigned short bits;
};

#if SEXP_USE_HUFF_SYMS
#include "opt/sexp-hufftabs.c"
static struct sexp_huff_entry huff_table[] = {
#include "opt/sexp-huff.c"
};
#endif

static int sexp_initialized_p = 0;

sexp sexp_read_float_tail(sexp ctx, sexp in, double whole, int negp);

static const char sexp_separators[] = {
  /* 1  2  3  4  5  6  7  8  9  a  b  c  d  e  f         */
  0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 0, 0, /* x0_ */
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* x1_ */
  1, 0, 1, 0, 0, 0, 0, 1, 1, 1, 0, 0, 1, 0, 0, 0, /* x2_ */
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, /* x3_ */
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, /* x4_ */
  0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, /* x5_ */
};

static int digit_value (int c) {
  return (((c)<='9') ? ((c) - '0') : ((toupper(c) - 'A') + 10));
}

static int hex_digit (int n) {
  return ((n<=9) ? ('0' + n) : ('A' + n - 10));
}

static int is_separator(int c) {
  return 0<c && c<0x60 && sexp_separators[c];
}

#if SEXP_USE_GLOBAL_SYMBOLS
sexp sexp_symbol_table[SEXP_SYMBOL_TABLE_SIZE];
#endif

sexp sexp_alloc_tagged_aux(sexp ctx, size_t size, sexp_uint_t tag sexp_current_source_param) {
  sexp res = (sexp) sexp_alloc(ctx, size);
  if (res && ! sexp_exceptionp(res)) {
    sexp_pointer_tag(res) = tag;
#if SEXP_USE_TRACK_ALLOC_SOURCE
    sexp_pointer_source(res) = source;
#endif
#if SEXP_USE_HEADER_MAGIC
    sexp_pointer_magic(res) = SEXP_POINTER_MAGIC;
#endif
  }
  return res;
}

sexp sexp_finalize_port (sexp ctx sexp_api_params(self, n), sexp port) {
  if (sexp_port_openp(port)) {
    sexp_port_openp(port) = 0;
    if (sexp_port_stream(port) && ! sexp_port_no_closep(port)) {
      fclose(sexp_port_stream(port));
      if (sexp_port_buf(port) && sexp_oportp(port))
	free(sexp_port_buf(port));
    }
  }
  return SEXP_VOID;
}

#if SEXP_USE_AUTOCLOSE_PORTS
#define SEXP_FINALIZE_PORT sexp_finalize_port
#else
#define SEXP_FINALIZE_PORT NULL
#endif

static struct sexp_type_struct _sexp_type_specs[] = {
  {SEXP_OBJECT, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, "object", SEXP_FALSE, SEXP_FALSE, NULL},
  {SEXP_TYPE, sexp_offsetof(type, cpl), 2, 2, 0, 0, sexp_sizeof(type), 0, 0, 0, 0, 0, 0, 0, 0, "type", SEXP_FALSE, SEXP_FALSE, NULL},
  {SEXP_FIXNUM, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, "integer", SEXP_FALSE, SEXP_FALSE, NULL},
  {SEXP_NUMBER, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, "number", SEXP_FALSE, SEXP_FALSE, NULL},
  {SEXP_CHAR, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, "char", SEXP_FALSE, SEXP_FALSE, NULL},
  {SEXP_BOOLEAN, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, "boolean", SEXP_FALSE, SEXP_FALSE, NULL},
  {SEXP_PAIR, sexp_offsetof(pair, car), 2, 3, 0, 0, sexp_sizeof(pair), 0, 0, 0, 0, 0, 0, 0, 0, "pair", SEXP_FALSE, SEXP_FALSE, NULL},
  {SEXP_SYMBOL, 0, 0, 0, 0, 0, sexp_sizeof(symbol)+1, sexp_offsetof(symbol, length), 1, 0, 0, 0, 0, 0, 0, "symbol", SEXP_FALSE, SEXP_FALSE, NULL},
  {SEXP_BYTES, 0, 0, 0, 0, 0, sexp_sizeof(bytes)+1, sexp_offsetof(bytes, length), 1, 0, 0, 0, 0, 0, 0, "byte-vector", SEXP_FALSE, SEXP_FALSE, NULL},
#if SEXP_USE_PACKED_STRINGS
  {SEXP_STRING, 0, 0, 0, 0, 0, sexp_sizeof(string)+1, sexp_offsetof(string, length), 1, 0, 0, 0, 0, 0, 0, "string", SEXP_FALSE, SEXP_FALSE, NULL},
#else
  {SEXP_STRING, sexp_offsetof(string, bytes), 1, 1, 0, 0, sexp_sizeof(string), 0, 0, 0, 0, 0, 0, 0, 0, "string", SEXP_FALSE, SEXP_FALSE, NULL},
#endif
  {SEXP_VECTOR, sexp_offsetof(vector, data), 0, 0, sexp_offsetof(vector, length), 1, sexp_sizeof(vector), sexp_offsetof(vector, length), sizeof(sexp), 0, 0, 0, 0, 0, 0, "vector", SEXP_FALSE, SEXP_FALSE, NULL},
  {SEXP_FLONUM, 0, 0, 0, 0, 0, sexp_sizeof(flonum), 0, 0, 0, 0, 0, 0, 0, 0, "real", SEXP_FALSE, SEXP_FALSE, NULL},
  {SEXP_BIGNUM, 0, 0, 0, 0, 0, sexp_sizeof(bignum), sexp_offsetof(bignum, length), sizeof(sexp_uint_t), 0, 0, 0, 0, 0, 0, "bignum", SEXP_FALSE, SEXP_FALSE, NULL},
  {SEXP_IPORT, sexp_offsetof(port, name), 2, 2, 0, 0, sexp_sizeof(port), 0, 0, 0, 0, 0, 0, 0, 0, "input-port", SEXP_FALSE, SEXP_FALSE, SEXP_FINALIZE_PORT},
  {SEXP_OPORT, sexp_offsetof(port, name), 2, 2, 0, 0, sexp_sizeof(port), 0, 0, 0, 0, 0, 0, 0, 0, "output-port", SEXP_FALSE, SEXP_FALSE, SEXP_FINALIZE_PORT},
  {SEXP_EXCEPTION, sexp_offsetof(exception, kind), 6, 6, 0, 0, sexp_sizeof(exception), 0, 0, 0, 0, 0, 0, 0, 0, "exception", SEXP_FALSE, SEXP_FALSE, NULL},
  {SEXP_PROCEDURE, sexp_offsetof(procedure, bc), 2, 2, 0, 0, sexp_sizeof(procedure), 0, 0, 0, 0, 0, 0, 0, 0, "procedure", SEXP_FALSE, SEXP_FALSE, NULL},
  {SEXP_MACRO, sexp_offsetof(macro, proc), 2, 2, 0, 0, sexp_sizeof(macro), 0, 0, 0, 0, 0, 0, 0, 0, "macro", SEXP_FALSE, SEXP_FALSE, NULL},
  {SEXP_SYNCLO, sexp_offsetof(synclo, env), 3, 3, 0, 0, sexp_sizeof(synclo), 0, 0, 0, 0, 0, 0, 0, 0, "syntactic-closure", SEXP_FALSE, SEXP_FALSE, NULL},
  {SEXP_ENV, sexp_offsetof(env, parent), 3, 3, 0, 0, sexp_sizeof(env), 0, 0, 0, 0, 0, 0, 0, 0, "environment", SEXP_FALSE, SEXP_FALSE, NULL},
  {SEXP_BYTECODE, sexp_offsetof(bytecode, name), 3, 3, 0, 0, sexp_sizeof(bytecode), offsetof(struct sexp_struct, value.bytecode.length), 1, 0, 0, 0, 0, 0, 0, "bytecode", SEXP_FALSE, SEXP_FALSE, NULL},
  {SEXP_CORE, 0, 0, 0, 0, 0, sexp_sizeof(core), 0, 0, 0, 0, 0, 0, 0, 0, "core-form", SEXP_FALSE, SEXP_FALSE, NULL},
  {SEXP_OPCODE, sexp_offsetof(opcode, data), 7, 7, 0, 0, sexp_sizeof(opcode), 0, 0, 0, 0, 0, 0, 0, 0, "opcode", SEXP_FALSE, SEXP_FALSE, NULL},
  {SEXP_LAMBDA, sexp_offsetof(lambda, name), 11, 11, 0, 0, sexp_sizeof(lambda), 0, 0, 0, 0, 0, 0, 0, 0, "lambda", SEXP_FALSE, SEXP_FALSE, NULL},
  {SEXP_CND, sexp_offsetof(cnd, test), 4, 4, 0, 0, sexp_sizeof(cnd), 0, 0, 0, 0, 0, 0, 0, 0, "conditional", SEXP_FALSE, SEXP_FALSE, NULL},
  {SEXP_REF, sexp_offsetof(ref, name), 3, 3, 0, 0, sexp_sizeof(ref), 0, 0, 0, 0, 0, 0, 0, 0, "reference", SEXP_FALSE, SEXP_FALSE, NULL},
  {SEXP_SET, sexp_offsetof(set, var), 3, 3, 0, 0, sexp_sizeof(set), 0, 0, 0, 0, 0, 0, 0, 0, "set!", SEXP_FALSE, SEXP_FALSE, NULL},
  {SEXP_SEQ, sexp_offsetof(seq, ls), 2, 2, 0, 0, sexp_sizeof(seq), 0, 0, 0, 0, 0, 0, 0, 0, "sequence", SEXP_FALSE, SEXP_FALSE, NULL},
  {SEXP_LIT, sexp_offsetof(lit, value), 2, 2, 0, 0, sexp_sizeof(lit), 0, 0, 0, 0, 0, 0, 0, 0, "literal", SEXP_FALSE, SEXP_FALSE, NULL},
  {SEXP_STACK, sexp_offsetof(stack, data), 1, 1, sexp_offsetof(stack, top), 1, sexp_sizeof(stack), offsetof(struct sexp_struct, value.stack.length), sizeof(sexp), 0, 0, 0, 0, 0, 0, "stack", SEXP_FALSE, SEXP_FALSE, NULL},
  {SEXP_CONTEXT, sexp_offsetof(context, bc), 13, 13, 0, 0, sexp_sizeof(context), 0, 0, 0, 0, 0, 0, 0, 0, "context", SEXP_FALSE, SEXP_FALSE, NULL},
  {SEXP_CPOINTER, sexp_offsetof(cpointer, parent), 1, 0, 0, 0, sexp_sizeof(cpointer), sexp_offsetof(cpointer, length), 1, 0, 0, 0, 0, 0, 0, "cpointer", SEXP_FALSE, SEXP_FALSE, NULL},
#if SEXP_USE_AUTO_FORCE
  {SEXP_PROMISE, sexp_offsetof(promise, thunk), 2, 2, 0, 0, sexp_sizeof(promise), 0, 0, 0, 0, 0, 0, 0, 0, "promise", SEXP_FALSE, SEXP_FALSE, NULL},
#endif
};

#if SEXP_USE_GLOBAL_TYPES
struct sexp_struct *sexp_type_specs = _sexp_type_specs;
#endif

#if SEXP_USE_TYPE_DEFS

#if SEXP_USE_GLOBAL_TYPES
static sexp_uint_t sexp_num_types = SEXP_NUM_CORE_TYPES;
static sexp_uint_t sexp_type_array_size = SEXP_NUM_CORE_TYPES;
#else
#define SEXP_INIT_NUM_TYPES (SEXP_NUM_CORE_TYPES*2)
#endif

sexp sexp_register_type_op (sexp ctx sexp_api_params(self, n), sexp name,
                            sexp parent, sexp slots,
                            sexp fb, sexp felb, sexp flb, sexp flo, sexp fls,
                            sexp sb, sexp so, sexp sc, sexp w, sexp wb, sexp wo,
                            sexp ws, sexp we, sexp_proc2 f) {
#if SEXP_USE_GLOBAL_TYPES
  struct sexp_struct *new, *tmp;
#else
  sexp *v1, *v2;
#endif
  sexp_gc_var2(res, type);
  sexp_uint_t i, len, num_types=sexp_context_num_types(ctx),
    type_array_size=sexp_context_type_array_size(ctx);
  sexp_gc_preserve2(ctx, res, type);
  if (num_types >= SEXP_MAXIMUM_TYPES) {
    res = sexp_user_exception(ctx, self, "register-type: exceeded maximum type limit", name);
  } else if (! sexp_stringp(name)) {
    res = sexp_type_exception(ctx, self, SEXP_STRING, name);
  } else {
    if (num_types >= type_array_size) {
      len = type_array_size*2;
      if (len > SEXP_MAXIMUM_TYPES) len = SEXP_MAXIMUM_TYPES;
#if SEXP_USE_GLOBAL_TYPES
      new = malloc(len * sizeof(_sexp_type_specs[0]));
      for (i=0; i<num_types; i++)
        memcpy(&(new[i]), &(sexp_type_specs[i]), sizeof(_sexp_type_specs[0]));
      tmp = sexp_type_specs;
      sexp_type_specs = new;
      if (type_array_size > num_types) free(tmp);
      sexp_type_array_size = len;
#else
      res = sexp_make_vector(ctx, sexp_make_fixnum(len), SEXP_VOID);
      if (sexp_exceptionp(res)) {
        sexp_gc_release2(ctx);
        return res;
      }
      v1 = sexp_vector_data(res);
      v2 = sexp_vector_data(sexp_global(ctx, SEXP_G_TYPES));
      for (i=0; i<num_types; i++)
        v1[i] = v2[i];
      sexp_global(ctx, SEXP_G_TYPES) = res;
#endif
    }
#if ! SEXP_USE_GLOBAL_TYPES
    sexp_type_by_index(ctx, num_types) = sexp_alloc_type(ctx, type, SEXP_TYPE);
#endif
    type = sexp_type_by_index(ctx, num_types);
    if (!sexp_exceptionp(type)) {
      sexp_pointer_tag(type) = SEXP_TYPE;
      sexp_type_tag(type) = num_types;
      sexp_type_slots(type) = slots;
      sexp_type_field_base(type) = sexp_unbox_fixnum(fb);
      sexp_type_field_eq_len_base(type) = sexp_unbox_fixnum(felb);
      sexp_type_field_len_base(type) = sexp_unbox_fixnum(flb);
      sexp_type_field_len_off(type) = sexp_unbox_fixnum(flo);
      sexp_type_field_len_scale(type) = sexp_unbox_fixnum(fls);
      sexp_type_size_base(type) = sexp_unbox_fixnum(sb);
      sexp_type_size_off(type) = sexp_unbox_fixnum(so);
      sexp_type_size_scale(type) = sexp_unbox_fixnum(sc);
      sexp_type_weak_base(type) = sexp_unbox_fixnum(w);
      sexp_type_weak_len_base(type) = sexp_unbox_fixnum(wb);
      sexp_type_weak_len_off(type) = sexp_unbox_fixnum(wo);
      sexp_type_weak_len_scale(type) = sexp_unbox_fixnum(ws);
      sexp_type_weak_len_extra(type) = sexp_unbox_fixnum(we);
      sexp_type_name(type) = strdup(sexp_string_data(name));
      sexp_type_finalize(type) = f;
      if (sexp_typep(parent)) {
        len = sexp_vectorp(sexp_type_cpl(parent)) ? sexp_vector_length(sexp_type_cpl(parent)) : 1;
        sexp_type_cpl(type) = sexp_make_vector(ctx, sexp_make_fixnum(len+1), SEXP_VOID);
        if (sexp_vectorp(sexp_type_cpl(parent)))
          memcpy(sexp_vector_data(sexp_type_cpl(type)),
                 sexp_vector_data(sexp_type_cpl(parent)),
                 len * sizeof(sexp));
        else
          sexp_vector_data(sexp_type_cpl(type))[len-1] = parent;
      } else {
        len = 0;
        sexp_type_cpl(type) = sexp_make_vector(ctx, SEXP_ONE, SEXP_VOID);
      }
      sexp_vector_data(sexp_type_cpl(type))[len] = type;
      sexp_type_depth(type) = len;
#if SEXP_USE_GLOBAL_TYPES
      sexp_num_types = num_types + 1;
#else
      sexp_global(ctx, SEXP_G_NUM_TYPES) = sexp_make_fixnum(num_types + 1);
#endif
    }
    res = type;
  }
  sexp_gc_release2(ctx);
  return res;
}

sexp sexp_register_simple_type_op (sexp ctx sexp_api_params(self, n), sexp name, sexp parent, sexp slots) {
  short i, num_slots = sexp_unbox_fixnum(sexp_length(ctx, slots));
  sexp type_size, num_slots_obj, cpl, tmp;
  if (parent && sexp_typep(parent)) {
    num_slots += sexp_unbox_fixnum(sexp_length(ctx, sexp_type_slots(parent)));
    if (sexp_vectorp((cpl = sexp_type_cpl(parent))))
      for (i=sexp_vector_length(cpl)-1; i>=0; i--) {
        tmp = sexp_vector_ref(cpl, sexp_make_fixnum(i));
        num_slots += sexp_unbox_fixnum(sexp_length(ctx, sexp_type_slots(tmp)));
      }
  }
  num_slots_obj = sexp_make_fixnum(num_slots);
  type_size = sexp_make_fixnum(sexp_sizeof_header + sizeof(sexp)*num_slots);
  return
    sexp_register_type(ctx, name, parent, slots,
                       sexp_make_fixnum(sexp_offsetof_slot0),
                       num_slots_obj, num_slots_obj, SEXP_ZERO, SEXP_ZERO,
                       type_size, SEXP_ZERO, SEXP_ZERO, SEXP_ZERO, SEXP_ZERO,
                       SEXP_ZERO, SEXP_ZERO, SEXP_ZERO, NULL);
}

sexp sexp_finalize_c_type (sexp ctx sexp_api_params(self, n), sexp obj) {
  if (sexp_cpointer_freep(obj))
    free(sexp_cpointer_value(obj));
  return SEXP_VOID;
}

#else
#define sexp_num_types SEXP_NUM_CORE_TYPES
#endif

#if ! SEXP_USE_BOEHM

#if ! SEXP_USE_MALLOC
#include "gc.c"
#endif

#endif  /* ! SEXP_USE_BOEHM */

/****************************** contexts ******************************/

void sexp_init_context_globals (sexp ctx) {
#if ! SEXP_USE_GLOBAL_TYPES
  sexp type, *vec;
  int i;
#endif
  sexp_context_globals(ctx)
    = sexp_make_vector(ctx, sexp_make_fixnum(SEXP_G_NUM_GLOBALS), SEXP_VOID);
#if ! SEXP_USE_GLOBAL_SYMBOLS
  sexp_global(ctx, SEXP_G_SYMBOLS) = sexp_make_vector(ctx, sexp_make_fixnum(SEXP_SYMBOL_TABLE_SIZE), SEXP_NULL);
#endif
#if SEXP_USE_FOLD_CASE_SYMS
  sexp_global(ctx, SEXP_G_FOLD_CASE_P) = sexp_make_boolean(SEXP_DEFAULT_FOLD_CASE_SYMS);
#endif
  sexp_global(ctx, SEXP_G_OOM_ERROR) = sexp_user_exception(ctx, SEXP_FALSE, "out of memory", SEXP_NULL);
  sexp_global(ctx, SEXP_G_OOS_ERROR) = sexp_user_exception(ctx, SEXP_FALSE, "out of stack space", SEXP_NULL);
  sexp_global(ctx, SEXP_G_QUOTE_SYMBOL) = sexp_intern(ctx, "quote", -1);
  sexp_global(ctx, SEXP_G_QUASIQUOTE_SYMBOL) = sexp_intern(ctx, "quasiquote", -1);
  sexp_global(ctx, SEXP_G_UNQUOTE_SYMBOL) = sexp_intern(ctx, "unquote", -1);
  sexp_global(ctx, SEXP_G_UNQUOTE_SPLICING_SYMBOL) = sexp_intern(ctx, "unquote-splicing", -1);
  sexp_global(ctx, SEXP_G_CUR_IN_SYMBOL) = sexp_intern(ctx, "current-input-port", -1);
  sexp_global(ctx, SEXP_G_CUR_OUT_SYMBOL) = sexp_intern(ctx, "current-output-port", -1);
  sexp_global(ctx, SEXP_G_CUR_ERR_SYMBOL) = sexp_intern(ctx, "current-error-port", -1);
  sexp_global(ctx, SEXP_G_INTERACTION_ENV_SYMBOL) = sexp_intern(ctx, "interaction-environment", -1);
  sexp_global(ctx, SEXP_G_EMPTY_VECTOR) = sexp_alloc_type(ctx, vector, SEXP_VECTOR);
  sexp_vector_length(sexp_global(ctx, SEXP_G_EMPTY_VECTOR)) = 0;
#if ! SEXP_USE_GLOBAL_TYPES
  sexp_global(ctx, SEXP_G_NUM_TYPES) = sexp_make_fixnum(SEXP_NUM_CORE_TYPES);
  sexp_global(ctx, SEXP_G_TYPES)
    = sexp_make_vector(ctx, sexp_make_fixnum(SEXP_INIT_NUM_TYPES), SEXP_VOID);
  vec = sexp_vector_data(sexp_global(ctx, SEXP_G_TYPES));
  for (i=0; i<SEXP_NUM_CORE_TYPES; i++) {
    type = sexp_alloc_type(ctx, type, SEXP_TYPE);
    memcpy(&(type->value), &(_sexp_type_specs[i]), sizeof(_sexp_type_specs[0]));
    vec[i] = type;
  }
#endif
}

#if ! SEXP_USE_GLOBAL_HEAP
sexp sexp_bootstrap_context (sexp_uint_t size, sexp_uint_t max_size) {
  sexp ctx;
  sexp_heap heap;
  struct sexp_struct dummy_ctx;
  if (size < SEXP_MINIMUM_HEAP_SIZE) size = SEXP_INITIAL_HEAP_SIZE;
  heap = sexp_make_heap(sexp_heap_align(size), sexp_heap_align(max_size));
  if (!heap) return 0;
  sexp_pointer_tag(&dummy_ctx) = SEXP_CONTEXT;
  sexp_context_saves(&dummy_ctx) = NULL;
  sexp_context_heap(&dummy_ctx) = heap;
  ctx = sexp_alloc_type(&dummy_ctx, context, SEXP_CONTEXT);
  if (!ctx || sexp_exceptionp(ctx)) {
    sexp_free_heap(heap);
  } else {
    sexp_context_heap(ctx) = heap;
  }
  return ctx;
}
#endif

sexp sexp_make_context (sexp ctx, size_t size, size_t max_size) {
  sexp_gc_var1(res);
  if (ctx) sexp_gc_preserve1(ctx, res);
#if ! SEXP_USE_GLOBAL_HEAP
  if (! ctx) {
    res = sexp_bootstrap_context(size, max_size);
    if (!res || sexp_exceptionp(res)) return res;
  } else
#endif
    {
      res = sexp_alloc_type(ctx, context, SEXP_CONTEXT);
#if ! SEXP_USE_BOEHM && ! SEXP_USE_MALLOC
      sexp_context_heap(res) = sexp_context_heap(ctx);
#endif
    }
  if (!res || sexp_exceptionp(res)) return res;
  sexp_context_parent(res) = ctx;
  sexp_context_lambda(res) = SEXP_FALSE;
  sexp_context_name(res) = sexp_context_specific(res) = SEXP_FALSE;
  sexp_context_fv(res) = SEXP_NULL;
  sexp_context_saves(res) = NULL;
  sexp_context_params(res) = SEXP_NULL;
  sexp_context_depth(res)=sexp_context_tracep(res)=sexp_context_pos(res)=0;
  sexp_context_tailp(res) = 1;
#if SEXP_USE_GREEN_THREADS
  sexp_context_event(res) = SEXP_FALSE;
  sexp_context_refuel(res) = SEXP_DEFAULT_QUANTUM;
#endif
  if (ctx) {
    sexp_context_globals(res) = sexp_context_globals(ctx);
    sexp_gc_release1(ctx);
  } else {
    sexp_init_context_globals(res);
  }
  return res;
}

#if ! SEXP_USE_GLOBAL_HEAP
void sexp_destroy_context (sexp ctx) {
  sexp_heap heap, tmp;
  size_t sum_freed;
  if (sexp_context_heap(ctx)) {
    heap = sexp_context_heap(ctx);
    sexp_markedp(ctx) = 1;
#if ! SEXP_USE_GLOBAL_TYPES
    sexp_markedp(sexp_context_globals(ctx)) = 1;
    sexp_markedp(sexp_global(ctx, SEXP_G_TYPES)) = 1;
#endif
    sexp_sweep(ctx, &sum_freed); /* sweep w/o mark to run finalizers */
    sexp_context_heap(ctx) = NULL;
    for ( ; heap; heap=tmp) {
      tmp = heap->next;
      sexp_free_heap(heap);
    }
  }
}
#endif

/***************************** exceptions *****************************/

sexp sexp_make_exception (sexp ctx, sexp kind, sexp message, sexp irritants,
                          sexp procedure, sexp source) {
  sexp exn = sexp_alloc_type(ctx, exception, SEXP_EXCEPTION);
  sexp_exception_kind(exn) = kind;
  sexp_exception_message(exn) = message;
  sexp_exception_irritants(exn) = irritants;
  sexp_exception_procedure(exn) = procedure;
  sexp_exception_source(exn) = source;
  return exn;
}

sexp sexp_string_cat3 (sexp ctx, char *pre, char *mid, char* suf) {
  int plen=strlen(pre), mlen=strlen(mid), slen=strlen(suf);
  char *s;
  sexp str;
  str = sexp_make_string(ctx, sexp_make_fixnum(plen+mlen+slen), SEXP_VOID);
  memcpy(s=sexp_string_data(str), pre, plen);
  memcpy(s+plen, mid, mlen);
  memcpy(s+plen+mlen, suf, slen);
  return str;
}

sexp sexp_user_exception (sexp ctx, sexp self, const char *ms, sexp ir) {
  sexp res;
  sexp_gc_var3(sym, str, irr);
  sexp_gc_preserve3(ctx, sym, str, irr);
  res = sexp_make_exception(ctx, sym = sexp_intern(ctx, "user", -1),
                            str = sexp_c_string(ctx, ms, -1),
                            ((sexp_pairp(ir) || sexp_nullp(ir))
                             ? ir : (irr = sexp_list1(ctx, ir))),
                            self, SEXP_FALSE);
  sexp_gc_release3(ctx);
  return res;
}

static sexp type_exception (sexp ctx, sexp self, sexp str, sexp obj, sexp src) {
  sexp_gc_var2(res, sym);
  sexp_gc_preserve2(ctx, res, sym);
  sym = sexp_intern(ctx, "type", -1);
  res = sexp_make_exception(ctx, sym, str, obj, self, src);
  sexp_exception_irritants(res)=sexp_list1(ctx, sexp_exception_irritants(res));
  sexp_gc_release2(ctx);
  return res;
}

sexp sexp_xtype_exception (sexp ctx, sexp self, const char *msg, sexp obj) {
  sexp_gc_var1(res);
  sexp_gc_preserve1(ctx, res);
  res = sexp_c_string(ctx, msg, -1);
  res = type_exception(ctx, self, res, obj, SEXP_FALSE);
  sexp_gc_release1(ctx);
  return res;
}

sexp sexp_type_exception (sexp ctx, sexp self, sexp_uint_t type_id, sexp obj) {
  sexp_gc_var1(res);
  sexp_gc_preserve1(ctx, res);
  res = sexp_string_cat3(ctx, "invalid type, expected ",
                         sexp_type_name_by_index(ctx, type_id), "");
  res = type_exception(ctx, self, res, obj, SEXP_FALSE);
  sexp_gc_release1(ctx);
  return res;
}

sexp sexp_range_exception (sexp ctx, sexp obj, sexp start, sexp end) {
  sexp_gc_var2(res, msg);
  sexp_gc_preserve2(ctx, res, msg);
  msg = sexp_c_string(ctx, "bad index range", -1);
  res = sexp_list2(ctx, start, end);
  res = sexp_cons(ctx, obj, res);
  res = sexp_make_exception(ctx, sexp_intern(ctx, "range", -1), msg, res,
                            SEXP_FALSE, SEXP_FALSE);
  sexp_gc_release2(ctx);
  return res;
}

sexp sexp_print_exception_op (sexp ctx sexp_api_params(self, n), sexp exn, sexp out) {
  sexp ls;
  if (! sexp_oportp(out))
    out = sexp_make_output_port(ctx, stderr, SEXP_FALSE);
  sexp_write_string(ctx, "ERROR", out);
  if (sexp_exceptionp(exn)) {
    if (sexp_exception_procedure(exn)) {
      if (sexp_procedurep(sexp_exception_procedure(exn))) {
        ls = sexp_bytecode_name(
              sexp_procedure_code(sexp_exception_procedure(exn)));
        if (ls && sexp_symbolp(ls)) {
          sexp_write_string(ctx, " in ", out);
          sexp_write(ctx, ls, out);
        }
      } else if (sexp_opcodep(sexp_exception_procedure(exn))) {
        sexp_write_string(ctx, " in ", out);
        sexp_write_string(ctx, sexp_opcode_name(sexp_exception_procedure(exn)), out);
      }
    }
    ls = sexp_exception_source(exn);
    if ((! (ls && sexp_pairp(ls)))
	&& sexp_exception_procedure(exn)
        && sexp_procedurep(sexp_exception_procedure(exn)))
      ls = sexp_bytecode_source(sexp_procedure_code(sexp_exception_procedure(exn)));
    if (ls && sexp_pairp(ls)) {
      if (sexp_fixnump(sexp_cdr(ls)) && (sexp_cdr(ls) >= SEXP_ZERO)) {
        sexp_write_string(ctx, " on line ", out);
        sexp_write(ctx, sexp_cdr(ls), out);
      }
      if (sexp_stringp(sexp_car(ls))) {
        sexp_write_string(ctx, " of file ", out);
        sexp_write_string(ctx, sexp_string_data(sexp_car(ls)), out);
      }
    }
    sexp_write_string(ctx, ": ", out);
    if (sexp_stringp(sexp_exception_message(exn)))
      sexp_write_string(ctx, sexp_string_data(sexp_exception_message(exn)), out);
    else
      sexp_write(ctx, sexp_exception_message(exn), out);
    if (sexp_exception_irritants(exn)
        && sexp_pairp(sexp_exception_irritants(exn))) {
      if (sexp_nullp(sexp_cdr(sexp_exception_irritants(exn)))) {
        sexp_write_string(ctx, ": ", out);
        sexp_write(ctx, sexp_car(sexp_exception_irritants(exn)), out);
        sexp_write_string(ctx, "\n", out);
      } else {
        sexp_write_string(ctx, "\n", out);
        for (ls=sexp_exception_irritants(exn);
             sexp_pairp(ls); ls=sexp_cdr(ls)) {
          sexp_write_string(ctx, "    ", out);
          sexp_write(ctx, sexp_car(ls), out);
          sexp_write_char(ctx, '\n', out);
        }
      }
    } else {
      sexp_write_char(ctx, '\n', out);
    }
  } else {
    sexp_write_string(ctx, ": ", out);
    if (sexp_stringp(exn))
      sexp_write_string(ctx, sexp_string_data(exn), out);
    else
      sexp_write(ctx, exn, out);
    sexp_write_char(ctx, '\n', out);
  }
  return SEXP_VOID;
}

static sexp sexp_read_error (sexp ctx, const char *msg, sexp ir, sexp port) {
  sexp res;
  sexp_gc_var4(sym, name, str, irr);
  sexp_gc_preserve4(ctx, sym, name, str, irr);
  name = (sexp_port_name(port) ? sexp_port_name(port) : SEXP_FALSE);
  name = sexp_cons(ctx, name, sexp_make_fixnum(sexp_port_line(port)));
  str = sexp_c_string(ctx, msg, -1);
  irr = ((sexp_pairp(ir) || sexp_nullp(ir)) ? ir : sexp_list1(ctx, ir));
  res = sexp_make_exception(ctx, sym = sexp_intern(ctx, "read", -1),
                            str, irr, SEXP_FALSE, name);
  sexp_gc_release4(ctx);
  return res;
}

/*************************** list utilities ***************************/

sexp sexp_cons_op (sexp ctx sexp_api_params(self, n), sexp head, sexp tail) {
  sexp pair = sexp_alloc_type(ctx, pair, SEXP_PAIR);
  if (sexp_exceptionp(pair)) return pair;
  sexp_car(pair) = head;
  sexp_cdr(pair) = tail;
  sexp_pair_source(pair) = SEXP_FALSE;
  return pair;
}

sexp sexp_list2 (sexp ctx, sexp a, sexp b) {
  sexp_gc_var1(res);
  sexp_gc_preserve1(ctx, res);
  res = sexp_cons(ctx, b, SEXP_NULL);
  res = sexp_cons(ctx, a, res);
  sexp_gc_release1(ctx);
  return res;
}

sexp sexp_listp_op (sexp ctx sexp_api_params(self, n), sexp hare) {
  sexp turtle;
  if (! sexp_pairp(hare))
    return sexp_make_boolean(sexp_nullp(hare));
  turtle = hare;
  hare = sexp_cdr(hare);
  for ( ; sexp_pairp(hare); turtle=sexp_cdr(turtle)) {
    if (hare == turtle) return SEXP_FALSE;
    hare = sexp_cdr(hare);
    if (sexp_pairp(hare)) hare = sexp_cdr(hare);
  }
  return sexp_make_boolean(sexp_nullp(hare));
}

sexp sexp_memq_op (sexp ctx sexp_api_params(self, n), sexp x, sexp ls) {
  while (sexp_pairp(ls))
    if (x == sexp_car(ls))
      return ls;
    else
      ls = sexp_cdr(ls);
  return SEXP_FALSE;
}

sexp sexp_assq_op (sexp ctx sexp_api_params(self, n), sexp x, sexp ls) {
  while (sexp_pairp(ls))
    if (sexp_pairp(sexp_car(ls)) && (x == sexp_caar(ls)))
      return sexp_car(ls);
    else
      ls = sexp_cdr(ls);
  return SEXP_FALSE;
}

sexp sexp_reverse_op (sexp ctx sexp_api_params(self, n), sexp ls) {
  sexp_gc_var1(res);
  sexp_gc_preserve1(ctx, res);
  for (res=SEXP_NULL; sexp_pairp(ls); ls=sexp_cdr(ls))
    res = sexp_cons(ctx, sexp_car(ls), res);
  sexp_gc_release1(ctx);
  return res;
}

sexp sexp_nreverse_op (sexp ctx sexp_api_params(self, n), sexp ls) {
  sexp a, b, tmp;
  if (ls == SEXP_NULL) return ls;
  sexp_assert_type(ctx, sexp_pairp, SEXP_PAIR, ls);
  b = ls;
  a = sexp_cdr(ls);
  sexp_cdr(b) = SEXP_NULL;
  for ( ; sexp_pairp(a); b=a, a=tmp) {
    tmp = sexp_cdr(a);
    sexp_cdr(a) = b;
  }
  return b;
}

sexp sexp_copy_list_op (sexp ctx sexp_api_params(self, n), sexp ls) {
  sexp tmp;
  sexp_gc_var1(res);
  if (! sexp_pairp(ls)) return ls;
  sexp_gc_preserve1(ctx, res);
  tmp = res = sexp_cons(ctx, sexp_car(ls), sexp_cdr(ls));
  for (ls=sexp_cdr(ls); sexp_pairp(ls); ls=sexp_cdr(ls), tmp=sexp_cdr(tmp))
    sexp_cdr(tmp) = sexp_cons(ctx, sexp_car(ls), sexp_cdr(ls));
  sexp_gc_release1(ctx);
  return res;
}

sexp sexp_append2_op (sexp ctx sexp_api_params(self, n), sexp a, sexp b) {
  sexp_gc_var2(a1, b1);
  sexp_gc_preserve2(ctx, a1, b1);
  b1 = b;
  for (a1=sexp_reverse(ctx, a); sexp_pairp(a1); a1=sexp_cdr(a1))
    b1 = sexp_cons(ctx, sexp_car(a1), b1);
  sexp_gc_release2(ctx);
  return b1;
}

sexp sexp_length_op (sexp ctx sexp_api_params(self, n), sexp ls) {
  sexp_uint_t res=0;
  for ( ; sexp_pairp(ls); res++, ls=sexp_cdr(ls))
    ;
  return sexp_make_fixnum(res);
}

sexp sexp_equalp_op (sexp ctx sexp_api_params(self, n), sexp a, sexp b) {
  sexp_uint_t size;
  sexp_sint_t i, len;
  sexp t, *p, *q;
  char *p0, *q0;

 loop:
  if (a == b)
    return SEXP_TRUE;
  else if ((! sexp_pointerp(a)) || (! sexp_pointerp(b))
           || (sexp_pointer_tag(a) != sexp_pointer_tag(b)))
    return SEXP_FALSE;

  /* a and b are both pointers of the same type */
#if SEXP_USE_BIGNUMS
  if (sexp_pointer_tag(a) == SEXP_BIGNUM)
    return sexp_make_boolean(!sexp_bignum_compare(a, b));
#endif
#if SEXP_USE_FLONUMS && ! SEXP_USE_IMMEDIATE_FLONUMS
  if (sexp_pointer_tag(a) == SEXP_FLONUM)
    return sexp_make_boolean(sexp_flonum_value(a) == sexp_flonum_value(b));
#endif
  t = sexp_object_type(ctx, a);
  p0 = ((char*)a) + offsetof(struct sexp_struct, value);
  p = (sexp*) (((char*)a) + sexp_type_field_base(t));
  q0 = ((char*)b) + offsetof(struct sexp_struct, value);
  q = (sexp*) (((char*)b) + sexp_type_field_base(t));
  if ((sexp)p == a) {p=(sexp*)p0; q=(sexp*)q0;}
  /* check preliminary non-object data */
  if ((p0 < (char*)p) && memcmp(p0, q0, ((char*)p - p0)))
    return SEXP_FALSE;
  /* check trailing non-object data */
  size = sexp_type_size_of_object(t, a) - offsetof(struct sexp_struct, value);
  p0 = ((char*)p + sexp_type_num_slots_of_object(t,a)*sizeof(sexp));
  if (((char*)a + size) > p0) {
    q0 = ((char*)q + sexp_type_num_slots_of_object(t,b)*sizeof(sexp));
    if (size != sexp_type_size_of_object(t,b)-offsetof(struct sexp_struct,value))
      return SEXP_FALSE;
    if (memcmp(p0, q0, size))
      return SEXP_FALSE;
  }
  /* check eq-object slots */
  len = sexp_type_num_eq_slots_of_object(t, a);
  if (len > 0) {
    for (i=0; i<len-1; i++)
      if (p[i] != q[i] && sexp_not(sexp_equalp(ctx, p[i], q[i])))
        return SEXP_FALSE;
    /* tail-recurse on the last value */
    a = p[len-1]; b = q[len-1]; goto loop;
  }
  return SEXP_TRUE;
}

/********************* strings, symbols, vectors **********************/

#if ! SEXP_USE_IMMEDIATE_FLONUMS
sexp sexp_make_flonum (sexp ctx, double f) {
  sexp x = sexp_alloc_type(ctx, flonum, SEXP_FLONUM);
  if (sexp_exceptionp(x)) return x;
  sexp_flonum_value(x) = f;
  return x;
}
#else
sexp sexp_flonump_op (sexp ctx sexp_api_params(self, n), sexp x) {
  return sexp_make_boolean(sexp_flonump(x));
}
#if SEXP_64_BIT
float sexp_flonum_value (sexp x) {
  union sexp_flonum_conv r;
  r.bits = (sexp_uint_t)x >> 32;
  return r.flonum;
}
sexp sexp_make_flonum (sexp ctx, float f) {
  union sexp_flonum_conv x;
  x.flonum = f;
  return (sexp)(((sexp_uint_t)(x.bits) << 32) + SEXP_IFLONUM_TAG);
}
#endif
#endif

sexp sexp_make_bytes_op (sexp ctx sexp_api_params(self, n), sexp len, sexp i) {
  sexp_sint_t clen = sexp_unbox_fixnum(len);
  sexp s;
  sexp_assert_type(ctx, sexp_fixnump, SEXP_FIXNUM, len);
  if (clen < 0) return sexp_xtype_exception(ctx, self, "negative length", len);
  s = sexp_alloc_atomic(ctx, sexp_sizeof(bytes)+clen+1);
  if (sexp_exceptionp(s)) return s;
  sexp_pointer_tag(s) = SEXP_BYTES;
#if SEXP_USE_HEADER_MAGIC
  sexp_pointer_magic(s) = SEXP_POINTER_MAGIC;
#endif
  sexp_bytes_length(s) = clen;
  if (sexp_fixnump(i))
    memset(sexp_bytes_data(s), sexp_unbox_fixnum(i), clen);
  sexp_bytes_data(s)[clen] = '\0';
  return s;
}

#if SEXP_USE_UTF8_STRINGS

static int sexp_utf8_initial_byte_count (int c) {
  if (c < 0xC0) return 1;
  if (c < 0xE0) return 2;
  return ((c>>4)&1)+3;
}

static int sexp_utf8_char_byte_count (int c) {
  if (c < 0x80) return 1;
  if (c < 0x800) return 2;
  if (c < 0x10000) return 3;
  return 4;
}

void sexp_utf8_encode_char (unsigned char* p, int len, int c) {
  switch (len) {
  case 4:  *p++ = (0xF0 + ((c)>>18)); *p++ = (0x80 + ((c>>12)&0x3F));
    *p++ = (0x80 + ((c>>6)&0x3F));    *p = (0x80 + (c&0x3F)); break;
  case 3:  *p++ = (0xE0 + ((c)>>12)); *p++ = (0x80 + ((c>>6)&0x3F));
    *p = (0x80 + (c&0x3F)); break;
  case 2:  *p++ = (0xC0 + ((c)>>6));  *p = (0x80 + (c&0x3F)); break;
  default: *p = c; break;
  }
}

sexp sexp_string_index_to_offset (sexp ctx sexp_api_params(self, n), sexp str, sexp index) {
  sexp_sint_t i, j, limit;
  unsigned char *p;
  sexp_assert_type(ctx, sexp_stringp, SEXP_STRING, str);
  sexp_assert_type(ctx, sexp_fixnump, SEXP_FIXNUM, index);
  p = (unsigned char*)sexp_string_data(str);
  limit = sexp_string_length(str);
  for (j=0, i=sexp_unbox_fixnum(index); i>0 && j<limit; i--)
    j += sexp_utf8_initial_byte_count(p[j]);
  if (i>0)
    return sexp_user_exception(ctx, self, "string-index->offset: index out of range", index);
  return sexp_make_fixnum(j);
}

#endif

sexp sexp_make_string_op (sexp ctx sexp_api_params(self, n), sexp len, sexp ch)
{
  sexp i = (sexp_charp(ch) ? sexp_make_fixnum(sexp_unbox_character(ch)) : ch);
  sexp_gc_var2(b, s);
#if SEXP_USE_UTF8_STRINGS
  int j, clen;
  if (sexp_charp(ch) && (sexp_unbox_character(ch) >= 0x80)) {
    sexp_assert_type(ctx, sexp_fixnump, SEXP_FIXNUM, len);
    clen = sexp_utf8_char_byte_count(sexp_unbox_character(ch));
    b = sexp_make_bytes_op(ctx sexp_api_pass(self, n),
                           sexp_fx_mul(len, sexp_make_fixnum(clen)), SEXP_VOID);
    for (j=0; j<sexp_unbox_fixnum(len); j++)
      sexp_utf8_encode_char((unsigned char*)sexp_bytes_data(b)+(j*clen), clen,
                            sexp_unbox_character(ch));
  } else
#endif
  b = sexp_make_bytes_op(ctx sexp_api_pass(self, n), len, i);
  if (sexp_exceptionp(b)) return b;
#if SEXP_USE_PACKED_STRINGS
  sexp_pointer_tag(b) = SEXP_STRING;
  return b;
#else
  sexp_gc_preserve2(ctx, b, s);
  s = sexp_alloc_type(ctx, string, SEXP_STRING);
  sexp_string_bytes(s) = b;
  sexp_string_offset(s) = 0;
  sexp_string_length(s) = sexp_bytes_length(b);
  sexp_gc_release2(ctx);
  return s;
#endif
}

sexp sexp_c_string (sexp ctx, const char *str, sexp_sint_t slen) {
  sexp_sint_t len = ((slen >= 0) ? slen : strlen(str));
  sexp s = sexp_make_string(ctx, sexp_make_fixnum(len), SEXP_VOID);
  memcpy(sexp_string_data(s), str, len);
  sexp_string_data(s)[len] = '\0';
  return s;
}

sexp sexp_substring_op (sexp ctx sexp_api_params(self, n), sexp str, sexp start, sexp end) {
  sexp res;
  sexp_assert_type(ctx, sexp_stringp, SEXP_STRING, str);
  sexp_assert_type(ctx, sexp_fixnump, SEXP_FIXNUM, start);
  if (sexp_not(end))
    end = sexp_make_fixnum(sexp_string_length(str));
  sexp_assert_type(ctx, sexp_fixnump, SEXP_FIXNUM, end);
  if ((sexp_unbox_fixnum(start) < 0)
      || (sexp_unbox_fixnum(start) > sexp_string_length(str))
      || (sexp_unbox_fixnum(end) < 0)
      || (sexp_unbox_fixnum(end) > sexp_string_length(str))
      || (end < start))
    return sexp_range_exception(ctx, str, start, end);
  res = sexp_make_string(ctx, sexp_fx_sub(end, start), SEXP_VOID);
  memcpy(sexp_string_data(res),
         sexp_string_data(str)+sexp_unbox_fixnum(start),
         sexp_string_length(res));
  sexp_string_data(res)[sexp_string_length(res)] = '\0';
  return res;
}

#if SEXP_USE_UTF8_STRINGS
sexp sexp_utf8_substring_op (sexp ctx sexp_api_params(self, n), sexp str, sexp start, sexp end) {
  sexp_assert_type(ctx, sexp_stringp, SEXP_STRING, str);
  sexp_assert_type(ctx, sexp_fixnump, SEXP_FIXNUM, start);
  start = sexp_string_index_to_offset(ctx sexp_api_pass(self, n), str, start);
  if (sexp_fixnump(end))
    end = sexp_string_index_to_offset(ctx sexp_api_pass(self, n), str, end);
  return sexp_substring_op(ctx sexp_api_pass(self, n), str, start, end);
}
#endif

sexp sexp_string_concatenate_op (sexp ctx sexp_api_params(self, n), sexp str_ls, sexp sep) {
  sexp res, ls;
  sexp_uint_t len=0, i=0, sep_len=0;
  char *p, *csep=NULL;
  for (ls=str_ls; sexp_pairp(ls); ls=sexp_cdr(ls), i++)
    if (! sexp_stringp(sexp_car(ls)))
      return sexp_type_exception(ctx, self, SEXP_STRING, sexp_car(ls));
    else
      len += sexp_string_length(sexp_car(ls));
  if (sexp_stringp(sep) && ((sep_len=sexp_string_length(sep)) > 0)) {
    csep = sexp_string_data(sep);
    len += sep_len*(i-1);
  }
  res = sexp_make_string(ctx, sexp_make_fixnum(len), SEXP_VOID);
  p = sexp_string_data(res);
  for (ls=str_ls; sexp_pairp(ls); ls=sexp_cdr(ls)) {
    len = sexp_string_length(sexp_car(ls));
    memcpy(p, sexp_string_data(sexp_car(ls)), len);
    p += len;
    if (sep_len && sexp_pairp(sexp_cdr(ls))) {
      memcpy(p, csep, sep_len);
      p += sep_len;
    }
  }
  *p = '\0';
  return res;
}

#define FNV_PRIME 16777619
#define FNV_OFFSET_BASIS 2166136261uL

#if SEXP_USE_HASH_SYMS

static sexp_uint_t sexp_string_hash(const char *str, sexp_sint_t len,
                                    sexp_uint_t acc) {
  for ( ; len; len--) {acc *= FNV_PRIME; acc ^= *str++;}
  return acc;
}

#endif

sexp sexp_intern(sexp ctx, const char *str, sexp_sint_t len) {
#if SEXP_USE_HUFF_SYMS
  struct sexp_huff_entry he;
  sexp_uint_t space=3, newbits;
  char c;
#endif
  sexp_uint_t res=FNV_OFFSET_BASIS, bucket, i=0;
  const char *p=str;
  sexp ls, tmp;
  sexp_gc_var1(sym);

  if (len < 0) len = strlen(str);

#if SEXP_USE_HUFF_SYMS
  res = 0;
  for ( ; i<len; i++, p++) {
    c = *p;
    if ((unsigned char)c > 127)
      goto normal_intern;
    he = huff_table[(unsigned char)c];
    newbits = he.len;
    if ((space+newbits) > (sizeof(sexp)*8))
      goto normal_intern;
    res |= (((sexp_uint_t) he.bits) << space);
    space += newbits;
  }
  return (sexp) (res + SEXP_ISYMBOL_TAG);

 normal_intern:
#endif
#if SEXP_USE_HASH_SYMS
  bucket = (sexp_string_hash(p, len-i, res) % SEXP_SYMBOL_TABLE_SIZE);
#else
  bucket = 0;
#endif
  for (ls=sexp_context_symbols(ctx)[bucket]; sexp_pairp(ls); ls=sexp_cdr(ls))
    if ((sexp_symbol_length(tmp=sexp_car(ls)) == len)
        && ! strncmp(str, sexp_symbol_data(tmp), len))
      return sexp_car(ls);

  /* not found, make a new symbol */
  sexp_gc_preserve1(ctx, sym);
  sym = sexp_c_string(ctx, str, len);
  if (sexp_exceptionp(sym)) return sym;
#if ! SEXP_USE_PACKED_STRINGS
  sym = sexp_string_bytes(sym);
#endif
  sexp_pointer_tag(sym) = SEXP_SYMBOL;
  sexp_push(ctx, sexp_context_symbols(ctx)[bucket], sym);
  sexp_gc_release1(ctx);
  return sym;
}

sexp sexp_string_to_symbol_op (sexp ctx sexp_api_params(self, n), sexp str) {
  sexp_assert_type(ctx, sexp_stringp, SEXP_STRING, str);
  return sexp_intern(ctx, sexp_string_data(str), sexp_string_length(str));
}

sexp sexp_make_vector_op (sexp ctx sexp_api_params(self, n), sexp len, sexp dflt) {
  sexp vec, *x;
  int i, clen = sexp_unbox_fixnum(len);
  if (! clen) return sexp_global(ctx, SEXP_G_EMPTY_VECTOR);
  vec = sexp_alloc_tagged(ctx, sexp_sizeof(vector) + clen*sizeof(sexp),
                          SEXP_VECTOR);
  if (sexp_exceptionp(vec)) return vec;
  x = sexp_vector_data(vec);
  for (i=0; i<clen; i++)
    x[i] = dflt;
  sexp_vector_length(vec) = clen;
  return vec;
}

sexp sexp_list_to_vector_op (sexp ctx sexp_api_params(self, n), sexp ls) {
  int i;
  sexp x, *elts, vec = sexp_make_vector(ctx, sexp_length(ctx, ls), SEXP_VOID);
  if (sexp_exceptionp(vec)) return vec;
  elts = sexp_vector_data(vec);
  for (i=0, x=ls; sexp_pairp(x); i++, x=sexp_cdr(x))
    elts[i] = sexp_car(x);
  return vec;
}

sexp sexp_make_cpointer (sexp ctx, sexp_uint_t type_id, void *value,
                         sexp parent, int freep) {
  sexp ptr;
  if (! value) return SEXP_FALSE;
  ptr = sexp_alloc_type(ctx, cpointer, type_id);
  if (sexp_exceptionp(ptr)) return ptr;
  sexp_freep(ptr) = freep;
  sexp_cpointer_value(ptr) = value;
  sexp_cpointer_parent(ptr) = parent;
  sexp_cpointer_length(ptr) = 0;
  return ptr;
}

/************************ reading and writing *************************/

#if SEXP_USE_BIGNUMS
#include "opt/bignum.c"
#endif

#if SEXP_USE_STRING_STREAMS

#define SEXP_INIT_STRING_PORT_SIZE 128

#if SEXP_BSD

#define sexp_stream_ctx(vec) sexp_vector_ref((sexp)vec, SEXP_ZERO)
#define sexp_stream_buf(vec) sexp_vector_ref((sexp)vec, SEXP_ONE)
#define sexp_stream_size(vec) sexp_vector_ref((sexp)vec, SEXP_TWO)
#define sexp_stream_pos(vec) sexp_vector_ref((sexp)vec, SEXP_THREE)

#define sexp_stream_ctx_set(vec, x) sexp_vector_set((sexp)vec, SEXP_ZERO, x)
#define sexp_stream_buf_set(vec, x) sexp_vector_set((sexp)vec, SEXP_ONE, x)
#define sexp_stream_size_set(vec, x) sexp_vector_set((sexp)vec, SEXP_TWO, x)
#define sexp_stream_pos_set(vec, x) sexp_vector_set((sexp)vec, SEXP_THREE, x)

int sstream_read (void *vec, char *dst, int n) {
  sexp_uint_t len = sexp_unbox_fixnum(sexp_stream_size(vec));
  sexp_uint_t pos = sexp_unbox_fixnum(sexp_stream_pos(vec));
  if (pos >= len) return 0;
  if (n > (len - pos)) n = (len - pos);
  memcpy(dst, sexp_string_data(sexp_stream_buf(vec))+pos, n);
  sexp_stream_pos_set(vec, sexp_make_fixnum(pos + n));
  return n;
}

int sstream_write (void *vec, const char *src, int n) {
  sexp_uint_t len, pos, newpos;
  sexp newbuf;
  len = sexp_unbox_fixnum(sexp_stream_size(vec));
  pos = sexp_unbox_fixnum(sexp_stream_pos(vec));
  newpos = pos+n;
  if (newpos >= len) {
    newbuf = sexp_make_string(sexp_stream_ctx(vec),
                              sexp_make_fixnum(newpos*2),
                              SEXP_VOID);
    memcpy(sexp_string_data(newbuf),
           sexp_string_data(sexp_stream_buf(vec)),
           pos);
    sexp_stream_buf_set(vec, newbuf);
    sexp_stream_size_set(vec, sexp_make_fixnum(newpos*2));
  }
  memcpy(sexp_string_data(sexp_stream_buf(vec))+pos, src, n);
  sexp_stream_pos_set(vec, sexp_make_fixnum(newpos));
  return n;
}

off_t sstream_seek (void *vec, off_t offset, int whence) {
  sexp_sint_t pos;
  if (whence == SEEK_SET) {
    pos = offset;
  } else if (whence == SEEK_CUR) {
    pos = sexp_unbox_fixnum(sexp_stream_pos(vec)) + offset;
  } else {                      /* SEEK_END */
    pos = sexp_unbox_fixnum(sexp_stream_size(vec)) + offset;
  }
  sexp_stream_pos_set(vec, sexp_make_fixnum(pos));
  return pos;
}

sexp sexp_make_input_string_port_op (sexp ctx sexp_api_params(self, n), sexp str) {
  FILE *in;
  sexp res;
  sexp_gc_var1(cookie);
  sexp_gc_preserve1(ctx, cookie);
  cookie = sexp_make_vector(ctx, sexp_make_fixnum(4), SEXP_VOID);
  sexp_stream_ctx_set(cookie, ctx);
  sexp_stream_buf_set(cookie, str);
  sexp_stream_size_set(cookie, sexp_make_fixnum(sexp_string_length(str)));
  sexp_stream_pos_set(cookie, SEXP_ZERO);
  in = funopen(cookie, &sstream_read, NULL, &sstream_seek, NULL);
  res = sexp_make_input_port(ctx, in, SEXP_FALSE);
  sexp_port_cookie(res) = cookie;
  sexp_gc_release1(ctx);
  return res;
}

sexp sexp_make_output_string_port_op (sexp ctx sexp_api_params(self, n)) {
  FILE *out;
  sexp res, size;
  sexp_gc_var1(cookie);
  sexp_gc_preserve1(ctx, cookie);
  size = sexp_make_fixnum(SEXP_INIT_STRING_PORT_SIZE);
  cookie = sexp_make_vector(ctx, sexp_make_fixnum(4), SEXP_VOID);
  sexp_stream_ctx_set(cookie, ctx);
  sexp_stream_buf_set(cookie, sexp_make_string(ctx, size, SEXP_VOID));
  sexp_stream_size_set(cookie, size);
  sexp_stream_pos_set(cookie, SEXP_ZERO);
  out = funopen(cookie, NULL, &sstream_write, &sstream_seek, NULL);
  res = sexp_make_output_port(ctx, out, SEXP_FALSE);
  sexp_port_cookie(res) = cookie;
  sexp_gc_release1(ctx);
  return res;
}

sexp sexp_get_output_string_op (sexp ctx sexp_api_params(self, n), sexp port) {
  sexp cookie = sexp_port_cookie(port);
  fflush(sexp_port_stream(port));
  return sexp_substring(ctx,
                        sexp_stream_buf(cookie),
                        SEXP_ZERO,
                        sexp_stream_pos(cookie));
}

#else

sexp sexp_make_input_string_port_op (sexp ctx sexp_api_params(self, n), sexp str) {
  FILE *in;
  sexp res;
  sexp_assert_type(ctx, sexp_stringp, SEXP_STRING, str);
  if (sexp_string_length(str) == 0)
    in = fopen("/dev/null", "r");
  else
    in = fmemopen(sexp_string_data(str), sexp_string_length(str), "r");
  if (in) {
    res = sexp_make_input_port(ctx, in, SEXP_FALSE);
    if (sexp_string_length(str) == 0)
      sexp_port_name(res) = sexp_c_string(ctx, "/dev/null", -1);
    sexp_port_cookie(res) = str;  /* for gc preservation */
  } else {
    res = sexp_user_exception(ctx, SEXP_FALSE, "couldn't open string", str);
  }
  return res;
}

sexp sexp_make_output_string_port_op (sexp ctx sexp_api_params(self, n)) {
  sexp res = sexp_make_output_port(ctx, NULL, SEXP_FALSE);
  sexp_port_stream(res)
    = open_memstream(&sexp_port_buf(res), &sexp_port_size(res));
  return res;
}

sexp sexp_get_output_string_op (sexp ctx sexp_api_params(self, n), sexp port) {
  fflush(sexp_port_stream(port));
  return sexp_c_string(ctx, sexp_port_buf(port), sexp_port_size(port));
}

#endif

#else

#define SEXP_PORT_BUFFER_SIZE 4096

int sexp_buffered_read_char (sexp ctx, sexp p) {
  if (sexp_port_offset(p) < sexp_port_size(p)) {
    return sexp_port_buf(p)[sexp_port_offset(p)++];
  } else if (! sexp_port_stream(p)) {
    return EOF;
  } else {
    sexp_port_size(p)
      = fread(sexp_port_buf(p), 1, SEXP_PORT_BUFFER_SIZE, sexp_port_stream(p));
    sexp_port_offset(p) = 0;
    return ((sexp_port_offset(p) < sexp_port_size(p))
            ? sexp_port_buf(p)[sexp_port_offset(p)++] : EOF);
  }
}

sexp sexp_buffered_write_char (sexp ctx, int c, sexp p) {
  if (sexp_port_offset(p) >= sexp_port_size(p))
    sexp_buffered_flush(ctx, p);
  sexp_port_buf(p)[sexp_port_offset(p)++] = c;
  return SEXP_VOID;
}

sexp sexp_buffered_write_string_n (sexp ctx, const char *str,
                                   sexp_uint_t len, sexp p) {
  if (sexp_port_offset(p) >= sexp_port_size(p))
    sexp_buffered_flush(ctx, p);
  memcpy(sexp_port_buf(p)+sexp_port_offset(p), str, len);
  sexp_port_offset(p) += len;
  return SEXP_VOID;
}

sexp sexp_buffered_write_string (sexp ctx, const char *str, sexp p) {
  return sexp_buffered_write_string_n(ctx, str, strlen(str), p);
}

sexp sexp_buffered_flush (sexp ctx, sexp p) {
  sexp_gc_var1(tmp);
  if (! sexp_oportp(p))
    return sexp_type_exception(ctx, NULL, SEXP_OPORT, p);
  if (! sexp_port_openp(p))
    return sexp_user_exception(ctx, SEXP_FALSE, "port is closed", p);
  else {
    if (sexp_port_stream(p)) {
      fwrite(sexp_port_buf(p), 1, sexp_port_offset(p), sexp_port_stream(p));
      fflush(sexp_port_stream(p));
    } else if (sexp_port_offset(p) > 0) {
      sexp_gc_preserve1(ctx, tmp);
      tmp = sexp_c_string(ctx, sexp_port_buf(p), sexp_port_offset(p));
      sexp_push(ctx, sexp_port_cookie(p), tmp);
      sexp_gc_release1(ctx);
    }
    sexp_port_offset(p) = 0;
    return SEXP_VOID;
  }
}

sexp sexp_make_input_string_port_op (sexp ctx sexp_api_params(self, n), sexp str) {
  sexp res;
  sexp_assert_type(ctx, sexp_stringp, SEXP_STRING, str);
  res = sexp_make_input_port(ctx, NULL, SEXP_FALSE);
  if (sexp_exceptionp(res)) return res;
  sexp_port_cookie(res) = str;
  sexp_port_buf(res) = sexp_string_data(str);
  sexp_port_offset(res) = 0;
  sexp_port_size(res) = sexp_string_length(str);
  return res;
}

sexp sexp_make_output_string_port_op (sexp ctx sexp_api_params(self, n)) {
  sexp res = sexp_make_output_port(ctx, NULL, SEXP_FALSE);
  if (sexp_exceptionp(res)) return res;
  sexp_port_buf(res) = (char*) malloc(SEXP_PORT_BUFFER_SIZE);
  if (!sexp_port_buf(res)) {
    res = sexp_global(ctx, SEXP_G_OOM_ERROR);
  } else {
    sexp_port_size(res) = SEXP_PORT_BUFFER_SIZE;
    sexp_port_offset(res) = 0;
    sexp_port_cookie(res) = SEXP_NULL;
  }
  return res;
}

sexp sexp_get_output_string_op (sexp ctx sexp_api_params(self, n), sexp out) {
  sexp res;
  sexp_gc_var2(ls, tmp);
  sexp_gc_preserve2(ctx, ls, tmp);
  if (sexp_port_offset(out) > 0) {
    tmp = sexp_c_string(ctx, sexp_port_buf(out), sexp_port_offset(out));
    ls = sexp_cons(ctx, tmp, sexp_port_cookie(out));
  } else {
    ls = sexp_port_cookie(out);
  }
  res = sexp_string_concatenate(ctx, ls, SEXP_FALSE);
  sexp_gc_release2(ctx);
  return res;
}

#endif

sexp sexp_make_input_port (sexp ctx, FILE* in, sexp name) {
  sexp p = sexp_alloc_type(ctx, port, SEXP_IPORT);
  if (sexp_exceptionp(p)) return p;
  sexp_port_stream(p) = in;
  sexp_port_name(p) = name;
  sexp_port_line(p) = 1;
  sexp_port_flags(p) = SEXP_PORT_UNKNOWN_FLAGS;
  sexp_port_buf(p) = NULL;
  sexp_port_openp(p) = 1;
  sexp_port_no_closep(p) = 0;
  sexp_port_sourcep(p) = 0;
  sexp_port_blockedp(p) = 0;
#if SEXP_USE_FOLD_CASE_SYMS
  sexp_port_fold_casep(p) = sexp_truep(sexp_global(ctx, SEXP_G_FOLD_CASE_P));
#endif
  sexp_port_cookie(p) = SEXP_VOID;
  return p;
}

sexp sexp_make_output_port (sexp ctx, FILE* out, sexp name) {
  sexp p = sexp_make_input_port(ctx, out, name);
  if (sexp_exceptionp(p)) return p;
  sexp_pointer_tag(p) = SEXP_OPORT;
  return p;
}

#define NUMBUF_LEN 32

sexp sexp_write_one (sexp ctx, sexp obj, sexp out) {
#if SEXP_USE_HUFF_SYMS
  unsigned long res;
#endif
  unsigned long len, c;
  long i=0;
  double f;
  sexp x, *elts;
  char *str=NULL, numbuf[NUMBUF_LEN];

  if (! obj) {
    sexp_write_string(ctx, "#<null>", out); /* shouldn't happen */
  } else if (sexp_pointerp(obj)) {
    switch (sexp_pointer_tag(obj)) {
    case SEXP_PAIR:
      sexp_write_char(ctx, '(', out);
      sexp_write_one(ctx, sexp_car(obj), out);
      for (x=sexp_cdr(obj); sexp_pairp(x); x=sexp_cdr(x)) {
        sexp_write_char(ctx, ' ', out);
        sexp_write_one(ctx, sexp_car(x), out);
      }
      if (! sexp_nullp(x)) {
        sexp_write_string(ctx, " . ", out);
        sexp_write_one(ctx, x, out);
      }
      sexp_write_char(ctx, ')', out);
      break;
    case SEXP_VECTOR:
      len = sexp_vector_length(obj);
      elts = sexp_vector_data(obj);
      if (len == 0) {
        sexp_write_string(ctx, "#()", out);
      } else {
        sexp_write_string(ctx, "#(", out);
        sexp_write_one(ctx, elts[0], out);
        for (i=1; i<len; i++) {
          sexp_write_char(ctx, ' ', out);
          sexp_write_one(ctx, elts[i], out);
        }
        sexp_write_char(ctx, ')', out);
      }
      break;
#if ! SEXP_USE_IMMEDIATE_FLONUMS
    case SEXP_FLONUM:
      f = sexp_flonum_value(obj);
#if SEXP_USE_INFINITIES
      if (isinf(f) || isnan(f)) {
        numbuf[0] = (isinf(f) && f < 0 ? '-' : '+');
        strcpy(numbuf+1, isinf(f) ? "inf.0" : "nan.0");
      } else
#endif
      {
        i = snprintf(numbuf, NUMBUF_LEN, "%.15g", f);
        if (f == trunc(f) && ! strchr(numbuf, '.')) {
          numbuf[i++] = '.'; numbuf[i++] = '0'; numbuf[i++] = '\0';
        }
      }
      sexp_write_string(ctx, numbuf, out);
      break;
#endif
    case SEXP_PROCEDURE:
      sexp_write_string(ctx, "#<procedure ", out);
      x = sexp_bytecode_name(sexp_procedure_code(obj));
      sexp_write_one(ctx, sexp_synclop(x) ? sexp_synclo_expr(x): x, out);
      sexp_write_string(ctx, ">", out);
      break;
    case SEXP_SYNCLO:
      sexp_write_string(ctx, "#<sc ", out);
      sexp_write(ctx, sexp_synclo_expr(obj), out);
      sexp_write_string(ctx, ">", out);
      break;
    case SEXP_TYPE:
      sexp_write_string(ctx, "#<type ", out);
      sexp_write_string(ctx, sexp_type_name(obj), out);
      sexp_write_string(ctx, ">", out);
      break;
    case SEXP_STRING:
      sexp_write_char(ctx, '"', out);
      i = sexp_string_length(obj);
      str = sexp_string_data(obj);
      for ( ; i>0; str++, i--) {
        switch (str[0]) {
        case '\\': sexp_write_string(ctx, "\\\\", out); break;
        case '"': sexp_write_string(ctx, "\\\"", out); break;
        case '\n': sexp_write_string(ctx, "\\n", out); break;
        case '\r': sexp_write_string(ctx, "\\r", out); break;
        case '\t': sexp_write_string(ctx, "\\t", out); break;
        default: sexp_write_char(ctx, str[0], out);
        }
      }
      sexp_write_char(ctx, '"', out);
      break;
    case SEXP_SYMBOL:
      i = sexp_symbol_length(obj);
      str = sexp_symbol_data(obj);
      for ( ; i>0; str++, i--) {
        if ((str[0] == '\\') || is_separator(str[0]))
          sexp_write_char(ctx, '\\', out);
        sexp_write_char(ctx, str[0], out);
      }
      break;
#if SEXP_USE_BIGNUMS
    case SEXP_BIGNUM:
      sexp_write_bignum(ctx, obj, out, 10);
      break;
#endif
    case SEXP_OPCODE:
      sexp_write_string(ctx, "#<opcode ", out);
      sexp_write_string(ctx, sexp_opcode_name(obj), out);
      sexp_write_char(ctx, '>', out);
      break;
    default:
      i = sexp_pointer_tag(obj);
      sexp_write_string(ctx, "#<", out);
      sexp_write_string(ctx,
                        (i < sexp_context_num_types(ctx))
                        ? sexp_type_name_by_index(ctx, i) : "invalid",
                        out);
      sexp_write_char(ctx, '>', out);
      break;
    }
  } else if (sexp_fixnump(obj)) {
    snprintf(numbuf, NUMBUF_LEN, "%ld", (long)sexp_unbox_fixnum(obj));
    sexp_write_string(ctx, numbuf, out);
#if SEXP_USE_IMMEDIATE_FLONUMS
  } else if (sexp_flonump(obj)) {
    f = sexp_flonum_value(obj);
#if SEXP_USE_INFINITIES
    if (isinf(f) || isnan(f)) {
      numbuf[0] = (isinf(f) && f < 0 ? '-' : '+');
      strcpy(numbuf+1, isinf(f) ? "inf.0" : "nan.0");
    } else
#endif
    {
      i = snprintf(numbuf, NUMBUF_LEN, "%.8g", f);
      if (f == trunc(f) && ! strchr(numbuf, '.')) {
        numbuf[i++] = '.'; numbuf[i++] = '0'; numbuf[i++] = '\0';
      }
    }
    sexp_write_string(ctx, numbuf, out);
#endif
  } else if (sexp_charp(obj)) {
    if (obj == sexp_make_character(' '))
      sexp_write_string(ctx, "#\\space", out);
    else if (obj == sexp_make_character('\n'))
      sexp_write_string(ctx, "#\\newline", out);
    else if (obj == sexp_make_character('\r'))
      sexp_write_string(ctx, "#\\return", out);
    else if (obj == sexp_make_character('\t'))
      sexp_write_string(ctx, "#\\tab", out);
    else if ((33 <= sexp_unbox_character(obj))
             && (sexp_unbox_character(obj) < 127)) {
      sexp_write_string(ctx, "#\\", out);
      sexp_write_char(ctx, sexp_unbox_character(obj), out);
    } else {
      sexp_write_string(ctx, "#\\x", out);
      c = sexp_unbox_character(obj);
      if (c >= 0x100) {
        if (c >= 0x10000) {
          sexp_write_char(ctx, hex_digit((c>>20)&0x0F), out);
          sexp_write_char(ctx, hex_digit((c>>16)&0x0F), out);
        }
        sexp_write_char(ctx, hex_digit((c>>12)&0x0F), out);
        sexp_write_char(ctx, hex_digit((c>>8)&0x0F), out);
      }
      sexp_write_char(ctx, hex_digit((c>>4)&0x0F), out);
      sexp_write_char(ctx, hex_digit(c&0x0F), out);
    }
  } else if (sexp_symbolp(obj)) {

#if SEXP_USE_HUFF_SYMS
    if (sexp_isymbolp(obj)) {
      c = ((sexp_uint_t)obj)>>3;
      while (c) {
#include "opt/sexp-unhuff.c"
        sexp_write_char(ctx, res, out);
      }
    }
#endif

  } else {
    switch ((sexp_uint_t) obj) {
    case (sexp_uint_t) SEXP_NULL:
      sexp_write_string(ctx, "()", out); break;
    case (sexp_uint_t) SEXP_TRUE:
      sexp_write_string(ctx, "#t", out); break;
    case (sexp_uint_t) SEXP_FALSE:
      sexp_write_string(ctx, "#f", out); break;
    case (sexp_uint_t) SEXP_EOF:
      sexp_write_string(ctx, "#<eof>", out); break;
    case (sexp_uint_t) SEXP_UNDEF:
    case (sexp_uint_t) SEXP_VOID:
      sexp_write_string(ctx, "#<undef>", out); break;
    default:
      sexp_write_string(ctx, "#<invalid immediate>", out);
    }
  }
  return SEXP_VOID;
}

sexp sexp_write_op (sexp ctx sexp_api_params(self, n), sexp obj, sexp out) {
  sexp_assert_type(ctx, sexp_oportp, SEXP_OPORT, out);
  return sexp_write_one(ctx, obj, out);
}

sexp sexp_display_op (sexp ctx sexp_api_params(self, n), sexp obj, sexp out) {
  sexp res=SEXP_VOID;
  sexp_assert_type(ctx, sexp_oportp, SEXP_OPORT, out);
  if (sexp_stringp(obj))
    sexp_write_string(ctx, sexp_string_data(obj), out);
  else if (sexp_charp(obj))
    sexp_write_char(ctx, sexp_unbox_character(obj), out);
  else
    res = sexp_write_one(ctx, obj, out);
  return res;
}

sexp sexp_flush_output_op (sexp ctx sexp_api_params(self, n), sexp out) {
  sexp_flush(ctx, out);
  return SEXP_VOID;
}

#define INIT_STRING_BUFFER_SIZE 128

sexp sexp_read_string (sexp ctx, sexp in) {
  int c, i=0, size=INIT_STRING_BUFFER_SIZE;
  char initbuf[INIT_STRING_BUFFER_SIZE];
  char *buf=initbuf, *tmp;
  sexp res;

  for (c = sexp_read_char(ctx, in); c != '"'; c = sexp_read_char(ctx, in)) {
    if (c == '\\') {
      c = sexp_read_char(ctx, in);
      switch (c) {
      case 'n': c = '\n'; break;
      case 'r': c = '\r'; break; 
      case 't': c = '\t'; break;
      case 'x':
        c = sexp_read_char(ctx, in);
        if (isxdigit(c)) {
          c = digit_value(c)*16 + digit_value(sexp_read_char(ctx, in));
        } else {
          sexp_push_char(ctx, c, in); c = 'x';
        }
      }
    }
    if (c == EOF) {
      res = sexp_read_error(ctx, "premature end of string", SEXP_NULL, in);
      break;
    }
    buf[i++] = c;
    if (i >= size) {       /* expand buffer w/ malloc(), later free() it */
      tmp = (char*) malloc(size*2);
      memcpy(tmp, buf, i);
      if (size != INIT_STRING_BUFFER_SIZE) free(buf);
      buf = tmp;
      size *= 2;
    }
  }

  buf[i] = '\0';
  res = sexp_c_string(ctx, buf, i);
  if (size != INIT_STRING_BUFFER_SIZE) free(buf);
  return res;
}

sexp sexp_read_symbol (sexp ctx, sexp in, int init, int internp) {
  int c, i=0, size=INIT_STRING_BUFFER_SIZE;
  char initbuf[INIT_STRING_BUFFER_SIZE];
  char *buf=initbuf, *tmp;
  sexp res;
#if SEXP_USE_FOLD_CASE_SYMS
  int foldp = sexp_port_fold_casep(in);
  init = (foldp ? tolower(init) : init);
#endif

  if (init != EOF)
    buf[i++] = init;

  for (c = sexp_read_char(ctx, in); c != '"'; c = sexp_read_char(ctx, in)) {
#if SEXP_USE_FOLD_CASE_SYMS
    if (foldp) c = tolower(c);
#endif
    if (c == '\\') c = sexp_read_char(ctx, in);
    if (c == EOF || is_separator(c)) {
      sexp_push_char(ctx, c, in);
      break;
    }
    buf[i++] = c;
    if (i >= size) {       /* expand buffer w/ malloc(), later free() it */
      tmp = (char*) malloc(size*2);
      memcpy(tmp, buf, i);
      if (size != INIT_STRING_BUFFER_SIZE) free(buf);
      buf = tmp;
      size *= 2;
    }
  }

  buf[i] = '\0';
  res = (internp ? sexp_intern(ctx, buf, i) : sexp_c_string(ctx, buf, i));
  if (size != INIT_STRING_BUFFER_SIZE) free(buf);
  return res;
}

sexp sexp_read_float_tail (sexp ctx, sexp in, double whole, int negp) {
  sexp exponent=SEXP_VOID;
  double res=0.0, scale=0.1, e=0.0;
  int c;
  for (c=sexp_read_char(ctx, in);
       isdigit(c);
       c=sexp_read_char(ctx, in), scale*=0.1)
    res += digit_value(c)*scale;
  if (c=='e' || c=='E') {
    exponent = sexp_read_number(ctx, in, 10);
    if (sexp_exceptionp(exponent)) return exponent;
    e = (sexp_fixnump(exponent) ? sexp_unbox_fixnum(exponent)
         : sexp_flonump(exponent) ? sexp_flonum_value(exponent) : 0.0);
  } else if ((c!=EOF) && ! is_separator(c)) {
    return sexp_read_error(ctx, "invalid numeric syntax",
                           sexp_make_character(c), in);
  } else {
    sexp_push_char(ctx, c, in);
  }
#if SEXP_USE_FLONUMS
  res = (whole + res) * pow(10, e);
  if (negp) res *= -1;
  return sexp_make_flonum(ctx, res);
#else
  return sexp_make_fixnum((sexp_uint_t)whole);
#endif
}

sexp sexp_read_number (sexp ctx, sexp in, int base) {
  sexp den;
  sexp_uint_t res = 0, tmp;
  int c, digit, negativep = 0;

  c = sexp_read_char(ctx, in);
  if (c == '-') {
    negativep = 1;
    c = sexp_read_char(ctx, in);
  }

  for ( ; isxdigit(c); c=sexp_read_char(ctx, in)) {
    digit = digit_value(c);
    if ((digit < 0) || (digit >= base))
      break;
    tmp = res * base + digit;
#if SEXP_USE_BIGNUMS
    if ((tmp < res) || (tmp > SEXP_MAX_FIXNUM)) {
      sexp_push_char(ctx, c, in);
      return sexp_read_bignum(ctx, in, res, (negativep ? -1 : 1), base);
    }
#endif
    res = tmp;
  }

  if (c=='.' || c=='e' || c=='E') {
    if (base != 10)
      return sexp_read_error(ctx, "found non-base 10 float", SEXP_NULL, in);
    if (c!='.') sexp_push_char(ctx, c, in);
    return sexp_read_float_tail(ctx, in, res, negativep);
  } else if (c=='/') {
    den = sexp_read_number(ctx, in, base);
    if (! sexp_fixnump(den))
      return (sexp_exceptionp(den)
              ? den : sexp_read_error(ctx, "invalid rational syntax", den, in));
    return sexp_make_flonum(ctx, (double)(negativep ? -res : res)
                            / (double)sexp_unbox_fixnum(den));
  } else {
    if ((c!=EOF) && ! is_separator(c))
      return sexp_read_error(ctx, "invalid numeric syntax",
                             sexp_make_character(c), in);
    sexp_push_char(ctx, c, in);
  }

  return sexp_make_fixnum(negativep ? -res : res);
}

#if SEXP_USE_UTF8_STRINGS
static int sexp_decode_utf8_char(const unsigned char* s) {
  int i = s[0], len = strlen((const char*)s);
  if ((i >= 0xC0) && (i <= 0xF7) && (s[1]>>6 == 2)) {
    if ((i < 0xE0) && (len == 2)) {
      return ((i&0x3F)<<6) + (s[1]&0x3F);
    } else if ((i < 0xF0) && (len == 3) && (s[2]>>6 == 2)) {
      return ((i&0x1F)<<12) + ((s[1]&0x3F)<<6) + (s[2]&0x3F);
    } else if ((len == 4) && (s[2]>>6 == 2) && (s[3]>>6 == 2)) {
      return ((i&0x0F)<<16) + ((s[1]&0x3F)<<6) + ((s[2]&0x3F)<<6) + (s[3]&0x3F);
    }
  }
  return -1;
}
#endif

#if SEXP_USE_GREEN_THREADS
int sexp_maybe_block_port (sexp ctx, sexp in, int forcep) {
  sexp f;
  int c;
  if (sexp_port_stream(in) && sexp_port_fileno(in) >= 0) {
    if (sexp_port_flags(in) == SEXP_PORT_UNKNOWN_FLAGS)
      sexp_port_flags(in) = fcntl(sexp_port_fileno(in), F_GETFL);
    if (sexp_port_flags(in) & O_NONBLOCK) {
      if (!forcep
          && (((c = sexp_read_char(ctx, in)) == EOF)
              && (errno == EAGAIN)
              && sexp_opcodep((f=sexp_global(ctx, SEXP_G_THREADS_BLOCKER))))) {
        ((sexp_proc2)sexp_opcode_func(f))(ctx sexp_api_pass(f, 1), in);
        return 1;
      } else {
        if (!forcep) sexp_push_char(ctx, c, in);
        sexp_port_blockedp(in) = 1;
        fcntl(sexp_port_fileno(in), F_SETFL, sexp_port_flags(in) & ~O_NONBLOCK);
      }
    }
  }
  return 0;
}

void sexp_maybe_unblock_port (sexp ctx, sexp in) {
  if (sexp_port_blockedp(in)) {
    sexp_port_blockedp(in) = 0;
    fcntl(sexp_port_fileno(in), F_SETFL, sexp_port_flags(in));
  }
}
#endif

sexp sexp_read_raw (sexp ctx, sexp in) {
  char *str;
  int c1, c2, line;
  sexp tmp2;
  sexp_gc_var2(res, tmp);
  sexp_check_block_port(ctx, in, 0);
  sexp_gc_preserve2(ctx, res, tmp);

 scan_loop:
  switch (c1 = sexp_read_char(ctx, in)) {
  case EOF:
    res = SEXP_EOF;
    break;
  case ';':
    while ((c1 = sexp_read_char(ctx, in)) != EOF)
      if (c1 == '\n')
        break;
    /* ... FALLTHROUGH ... */
  case '\n':
    sexp_port_line(in)++;
    goto scan_loop;
  case ' ':
  case '\t':
  case '\r':
    goto scan_loop;
  case '\'':
    res = sexp_read(ctx, in);
    if (! sexp_exceptionp(res))
      res = sexp_list2(ctx, sexp_global(ctx, SEXP_G_QUOTE_SYMBOL), res);
    break;
  case '`':
    res = sexp_read(ctx, in);
    if (! sexp_exceptionp(res))
      res = sexp_list2(ctx, sexp_global(ctx, SEXP_G_QUASIQUOTE_SYMBOL), res);
    break;
  case ',':
    if ((c1 = sexp_read_char(ctx, in)) == '@') {
      res = sexp_read(ctx, in);
      if (! sexp_exceptionp(res))
        res = sexp_list2(ctx, sexp_global(ctx, SEXP_G_UNQUOTE_SPLICING_SYMBOL), res);
    } else {
      sexp_push_char(ctx, c1, in);
      res = sexp_read(ctx, in);
      if (! sexp_exceptionp(res))
        res = sexp_list2(ctx, sexp_global(ctx, SEXP_G_UNQUOTE_SYMBOL), res);
    }
    break;
  case '"':
    res = sexp_read_string(ctx, in);
    break;
  case '(':
    line = (sexp_port_sourcep(in) ? sexp_port_line(in) : -1);
    res = SEXP_NULL;
    tmp = sexp_read_raw(ctx, in);
    while ((tmp != SEXP_EOF) && (tmp != SEXP_CLOSE) && (tmp != SEXP_RAWDOT)) {
      if (sexp_exceptionp(tmp)) {
        res = tmp;
        break;
      }
      res = sexp_cons(ctx, tmp, res);
      if (sexp_port_sourcep(in) && (line >= 0))
        sexp_pair_source(res)
          = sexp_cons(ctx, sexp_port_name(in), sexp_make_fixnum(line));
      tmp = sexp_read_raw(ctx, in);
    }
    if (! sexp_exceptionp(res)) {
      if (tmp == SEXP_RAWDOT) { /* dotted list */
        if (res == SEXP_NULL) {
          res = sexp_read_error(ctx, "dot before any elements in list",
                                SEXP_NULL, in);
        } else {
          tmp = sexp_read_raw(ctx, in);
          if (sexp_exceptionp(tmp)) {
            res = tmp;
          } else if (tmp == SEXP_CLOSE) {
            res = sexp_read_error(ctx, "no final element in list after dot",
                                  SEXP_NULL, in);
          } else if (sexp_read_raw(ctx, in) != SEXP_CLOSE) {
            res = sexp_read_error(ctx, "multiple tokens in dotted tail",
                                  SEXP_NULL, in);
          } else {
            tmp2 = res;
            res = sexp_nreverse(ctx, res);
            sexp_cdr(tmp2) = tmp;
          }
        }
      } else if (tmp == SEXP_CLOSE) {
        res = (sexp_pairp(res) ? sexp_nreverse(ctx, res) : res);
      } else {
        res = sexp_read_error(ctx, "missing trailing ')'", SEXP_NULL, in);
      }
    }
    if ((line >= 0) && sexp_pairp(res)) {
      sexp_pair_source(res)
        = sexp_cons(ctx, sexp_port_name(in), sexp_make_fixnum(line));
    }
    if (sexp_port_sourcep(in))
      for (tmp=res; sexp_pairp(tmp); tmp=sexp_cdr(tmp))
        sexp_immutablep(tmp) = 1;
    break;
  case '#':
    switch (c1=sexp_read_char(ctx, in)) {
    case 'b':
      res = sexp_read_number(ctx, in, 2); break;
    case 'o':
      res = sexp_read_number(ctx, in, 8); break;
    case 'd':
      res = sexp_read_number(ctx, in, 10); break;
    case 'x':
      res = sexp_read_number(ctx, in, 16); break;
    case 'e':
      res = sexp_read(ctx, in);
      if (sexp_flonump(res))
        res = sexp_make_fixnum((sexp_sint_t)sexp_flonum_value(res));
      break;
    case 'i':
      res = sexp_read(ctx, in);
      if (sexp_fixnump(res))
        res = sexp_make_flonum(ctx, sexp_unbox_fixnum(res));
      break;
    case 'f': case 'F':
    case 't': case 'T':
      c2 = sexp_read_char(ctx, in);
      if (c2 == EOF || is_separator(c2)) {
        res = (tolower(c1) == 't' ? SEXP_TRUE : SEXP_FALSE);
        sexp_push_char(ctx, c2, in);
      } else {
        tmp = sexp_list2(ctx, sexp_make_character(c1), sexp_make_character(c2));
        res = sexp_read_error(ctx, "invalid syntax #%c%c", tmp, in);
      }
      break;
/*     case '0': case '1': case '2': case '3': case '4': */
/*     case '5': case '6': case '7': case '8': case '9': */
    case ';':
      tmp = sexp_read_raw(ctx, in);   /* discard */
      if (sexp_exceptionp(tmp))
        res = tmp;
      else
        goto scan_loop;
      break;
    case '!':
      while ((c1 = sexp_read_char(ctx, in)) != EOF)
        if (c1 == '\n')
          break;
      sexp_port_line(in)++;
      goto scan_loop;
    case '\\':
      c1 = sexp_read_char(ctx, in);
      res = sexp_read_symbol(ctx, in, c1, 0);
      if (sexp_stringp(res)) {
        str = sexp_string_data(res);
        if (sexp_string_length(res) == 0)
          res =
            sexp_read_error(ctx, "unexpected end of character literal",
                            SEXP_NULL, in);
        if (sexp_string_length(res) == 1) {
          res = sexp_make_character(c1);
        } else if ((c1 == 'x' || c1 == 'X') &&
                   (isxdigit)(str[1]) && (isxdigit)(str[2]) && str[3] == '\0') {
          res = sexp_make_character(16 * digit_value(str[1])
                                    + digit_value(str[2]));
        } else {
          if (strcasecmp(str, "space") == 0)
            res = sexp_make_character(' ');
          else if (strcasecmp(str, "newline") == 0)
            res = sexp_make_character('\n');
          else if (strcasecmp(str, "return") == 0)
            res = sexp_make_character('\r');
          else if (strcasecmp(str, "tab") == 0)
            res = sexp_make_character('\t');
#if SEXP_USE_UTF8_STRINGS
          else if ((c1=sexp_decode_utf8_char((unsigned char*)str)) > 0)
            res = sexp_make_character(c1);
#endif
          else {
            tmp = sexp_c_string(ctx, str, -1);
            res = sexp_read_error(ctx, "unknown character name", tmp, in);
          }
        }
      }
      break;
    case '(':
      sexp_push_char(ctx, c1, in);
      res = sexp_read(ctx, in);
      if (sexp_not(sexp_listp(ctx, res))) {
        if (! sexp_exceptionp(res)) {
          res = sexp_read_error(ctx, "dotted list not allowed in vector syntax",
                                SEXP_NULL,
                                in);
        }
      } else {
        res = sexp_list_to_vector(ctx, res);
      }
      break;
    default:
      res = sexp_read_error(ctx, "invalid # syntax",
                            sexp_make_character(c1), in);
    }
    break;
  case '.':
    c1 = sexp_read_char(ctx, in);
    sexp_push_char(ctx, c1, in);
    if (c1 == EOF || is_separator(c1)) {
      res = SEXP_RAWDOT;
    } else if (isdigit(c1)) {
      res = sexp_read_float_tail(ctx, in, 0, 0);
    } else {
      res = sexp_read_symbol(ctx, in, '.', 1);
    }
    break;
  case ')':
    res = SEXP_CLOSE;
    break;
  case '+':
  case '-':
    c2 = sexp_read_char(ctx, in);
    if (c2 == '.' || isdigit(c2)) {
      sexp_push_char(ctx, c2, in);
      res = sexp_read_number(ctx, in, 10);
      if ((c1 == '-') && ! sexp_exceptionp(res)) {
#if SEXP_USE_FLONUMS
        if (sexp_flonump(res))
#if SEXP_USE_IMMEDIATE_FLONUMS
          res = sexp_make_flonum(ctx, -1 * sexp_flonum_value(res));
#else
          sexp_flonum_value(res) = -1 * sexp_flonum_value(res);
#endif
        else
#endif
#if SEXP_USE_BIGNUMS
          if (sexp_bignump(res)) {
            if ((sexp_bignum_hi(res) == 1)
                && (sexp_bignum_data(res)[0] == (SEXP_MAX_FIXNUM+1)))
              res = sexp_make_fixnum(-sexp_bignum_data(res)[0]);
            else
              sexp_bignum_sign(res) = -sexp_bignum_sign(res);
          } else
#endif
            res = sexp_fx_mul(res, SEXP_NEG_ONE);
      }
    } else {
      sexp_push_char(ctx, c2, in);
      res = sexp_read_symbol(ctx, in, c1, 1);
#if SEXP_USE_INFINITIES
      if (res == sexp_intern(ctx, "+inf.0", -1))
        res = sexp_make_flonum(ctx, sexp_pos_infinity);
      else if (res == sexp_intern(ctx, "-inf.0", -1))
        res = sexp_make_flonum(ctx, sexp_neg_infinity);
      else if (res == sexp_intern(ctx, "+nan.0", -1))
        res = sexp_make_flonum(ctx, sexp_nan);
#endif
    }
    break;
  case '0': case '1': case '2': case '3': case '4':
  case '5': case '6': case '7': case '8': case '9':
    sexp_push_char(ctx, c1, in);
    res = sexp_read_number(ctx, in, 10);
    break;
  default:
    res = sexp_read_symbol(ctx, in, c1, 1);
    break;
  }

  if (sexp_port_sourcep(in) && sexp_pointerp(res))
    sexp_immutablep(res) = 1;
  sexp_maybe_unblock_port(ctx, in);
  sexp_gc_release2(ctx);
  return res;
}

sexp sexp_read_op (sexp ctx sexp_api_params(self, n), sexp in) {
  sexp res;
  sexp_assert_type(ctx, sexp_iportp, SEXP_IPORT, in);
  res = sexp_read_raw(ctx, in);
  if (res == SEXP_CLOSE)
    res = sexp_read_error(ctx, "too many ')'s", SEXP_NULL, in);
  if (res == SEXP_RAWDOT)
    res = sexp_read_error(ctx, "unexpected '.'", SEXP_NULL, in);
  return res;
}

sexp sexp_read_from_string (sexp ctx, const char *str, sexp_sint_t len) {
  sexp res;
  sexp_gc_var2(s, in);
  sexp_gc_preserve2(ctx, s, in);
  s = sexp_c_string(ctx, str, len);
  in = sexp_make_input_string_port(ctx, s);
  res = sexp_read(ctx, in);
  sexp_gc_release2(ctx);
  return res;
}

sexp sexp_string_to_number_op (sexp ctx sexp_api_params(self, n), sexp str, sexp b) {
  int base;
  sexp_gc_var1(in);
  sexp_assert_type(ctx, sexp_stringp, SEXP_STRING, str);
  sexp_assert_type(ctx, sexp_fixnump, SEXP_FIXNUM, b);
  if (((base=sexp_unbox_fixnum(b)) < 2) || (base > 36))
    return sexp_user_exception(ctx, self, "invalid numeric base", b);
  sexp_gc_preserve1(ctx, in);
  in = sexp_make_input_string_port(ctx, str);
  in = ((sexp_string_data(str)[0] == '#') ?
        sexp_read(ctx, in) : sexp_read_number(ctx, in, base));
  sexp_gc_release1(ctx);
  return sexp_numberp(in) ? in : SEXP_FALSE;
}

sexp sexp_write_to_string (sexp ctx, sexp obj) {
  sexp str;
  sexp_gc_var1(out);
  sexp_gc_preserve1(ctx, out);
  out = sexp_make_output_string_port(ctx);
  str = sexp_write(ctx, obj, out);
  if (! sexp_exceptionp(str))
    str = sexp_get_output_string(ctx, out);
  sexp_gc_release1(ctx);
  return str;
}

void sexp_init (void) {
#if SEXP_USE_GLOBAL_SYMBOLS
  int i;
#endif
  if (! sexp_initialized_p) {
    sexp_initialized_p = 1;
#if SEXP_USE_BOEHM
    GC_init();
#if SEXP_USE_GLOBAL_SYMBOLS
    GC_add_roots((char*)&sexp_symbol_table,
                 ((char*)&sexp_symbol_table)+sizeof(sexp_symbol_table)+1);
#endif
#elif ! SEXP_USE_MALLOC
    sexp_gc_init();
#endif
#if SEXP_USE_GLOBAL_SYMBOLS
    for (i=0; i<SEXP_SYMBOL_TABLE_SIZE; i++)
      sexp_symbol_table[i] = SEXP_NULL;
#endif
  }
}