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Each contexts keep a link to the heap which it is a part of (when using the native GC), as well as a vector of special globals that it needs quick access to (e.g. the `quote' and `quasiquote', etc. symbols. You can use this to manage multiple completely unrelated VMs in the same application, and everything will be thread-safe. The old behavior is still available by editing config.h, which now includes somewhat better descriptions of all the settings.
115 lines
3.9 KiB
Text
115 lines
3.9 KiB
Text
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Chibi-Scheme
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--------------
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Minimal Scheme Implementation for use as an Extension Language
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http://synthcode.com/wiki/chibi-scheme/
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Chibi-Scheme is a very small but mostly complete R5RS Scheme
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implementation using a reasonably fast custom VM. Chibi-Scheme tries
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as much as possible not to trade its small size by cutting corners,
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and provides full continuations, both low and high-level hygienic
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macros based on syntactic-closures, string ports and exceptions.
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Chibi-Scheme is written in highly portable C and supports multiple
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simultaneous VM instances to run.
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To build, just run "make". This will provide a shared library
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"libchibi-scheme", as well as a sample "chibi-scheme" command-line
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repl. The "chibi-scheme-static" make target builds an equivalent
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static executable.
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You can edit the file config.h for a number of settings, mostly
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disabling features to make the executable smaller. You can specify
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standard options directly as arguments to make, for example
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make CFLAGS=-Os
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to optimize for size, or
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make LDFLAGS=-L/usr/local/lib CPPFLAGS=-I/usr/local/include
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to compile against a library installed in /usr/local.
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By default Chibi uses a custom, precise, non-moving GC. You can link
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against the Boehm conservative GC by editing the config file, or
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directly from make with:
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make USE_BOEHM=1
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See the file main.c for an example of using chibi-scheme as a library.
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The essential functions to remember are:
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#include <chibi/eval.h>
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sexp_make_eval_context(NULL, NULL, NULL)
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returns a new context with a fresh stack and standard environment
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sexp_destroy_context(context)
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free a context and all associated memory
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sexp_eval(context, expr, env)
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evaluates an s-expression in an environment
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env can be NULL to use the context's default env
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sexp_eval_string(context, str)
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reads an s-expression from str and evaluates it
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sexp_load(context, file, env)
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read and eval all top-level forms from file
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sexp_context_env(context)
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a macro returning the environment associated with a context
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sexp_env_define(context, env, symbol, value)
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define a variable in an environment
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A minimal module system is provided by default. Currently you can
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load the following SRFIs with (import (srfi N)):
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1, 2, 6, 8, 9, 11, 16, 26, 69
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LOAD is extended to accept an optional environment argument, like
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EVAL. You can also LOAD shared libraries in addition to Scheme source
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files - in this case the function sexp_init_library is automatically
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called with the following signature:
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sexp_init_library(sexp context, sexp environment)
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To define new primitive functions from C, use sexp_define_foreign,
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which takes a Scheme environment, a name, a number of arguments the C
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function takes (not counting the context argument), and a C function.
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/* sexp_define_foreign(context, env, name, num_args, f) */
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sexp add (sexp context, sexp x, sexp y) {
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return sexp_fx_add(x, y);
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}
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sexp_define_foreign(context, env, "add", 2, add);
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You can also define functions with a single optional argument:
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sexp_define_foreign_opt(context, env, "add", 2, add, sexp_make_fixnum(1));
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See the SRFI-69 implementation for more detailed examples of this.
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You can define new data types with SRFI-9. This is just syntactic
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sugar for the following more primitive type constructors:
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(register-simple-type <name-string> <num-fields>)
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=> <type-id> ; a fixnum
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(make-type-predicate <opcode-name-string> <type-id>)
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=> <opcode> ; takes 1 arg, returns #t iff that arg is of the type
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(make-constructor <constructor-name-string> <type-id>)
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=> <opcode> ; takes 0 args, returns a newly allocated instance of type
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(make-getter <getter-name-string> <type-id> <field-index>)
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=> <opcode> ; takes 1 args, retrieves the field located at the index
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(make-setter <setter-name-string> <type-id> <field-index>)
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=> <opcode> ; takes 2 args, sets the field located at the index
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