From 741835bc499cec46e5c5fd73fbd15af1a0f3a933 Mon Sep 17 00:00:00 2001
From: Justin Ethier <justin.ethier@gmail.com>
Date: Thu, 11 Jun 2015 22:13:46 -0400
Subject: [PATCH] Return the "void" object from I/O functions

Primarily need this to prevent duplicate output in the REPL when calling functions such as (write).
---
 cyclone.h |  4 ----
 runtime.c | 19 +++++++++++--------
 runtime.h |  1 +
 3 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/cyclone.h b/cyclone.h
index 04d94a66..2d61eb68 100644
--- a/cyclone.h
+++ b/cyclone.h
@@ -87,10 +87,6 @@ typedef long tag_type;
 #define boolean_tag 15
 #define cvar_tag 16
 #define vector_tag 17
-/* TODO: need a type to return from things like
-   (if #f #t) and (write 1) so the REPL will not print
-   anything for them:
-  void_tag */
 
 #define nil NULL
 #define eq(x,y) (x == y)
diff --git a/runtime.c b/runtime.c
index 63a1bcae..5d55f005 100644
--- a/runtime.c
+++ b/runtime.c
@@ -68,6 +68,9 @@ const object boolean_f = &f_boolean;
 static symbol_type Cyc_191procedure_symbol = {symbol_tag, "procedure", nil};
 const object quote_Cyc_191procedure = &Cyc_191procedure_symbol;
 
+static symbol_type Cyc_void_symbol = {symbol_tag, "", nil};
+const object quote_void = &Cyc_void_symbol;
+
 /* Symbol Table */
 
 /* Notes for the symbol table
@@ -323,8 +326,8 @@ object Cyc_display(object x, FILE *port)
 {object tmp = nil;
  object has_cycle = boolean_f;
  int i = 0;
- if (nullp(x)) {fprintf(port, "()"); return x;}
- if (obj_is_char(x)) {fprintf(port, "%c", obj_obj2char(x)); return x;}
+ if (nullp(x)) {fprintf(port, "()"); return quote_void;}
+ if (obj_is_char(x)) {fprintf(port, "%c", obj_obj2char(x)); return quote_void;}
  switch (type_of(x))
    {case closure0_tag:
     case closure1_tag:
@@ -403,7 +406,7 @@ object Cyc_display(object x, FILE *port)
       break;
     default:
       fprintf(port, "Cyc_display: bad tag x=%ld\n", ((closure)x)->tag); getchar(); exit(0);}
- return x;}
+ return quote_void;}
 
 object dispatch_write_va(int argc, object clo, object cont, object x, ...) {
   object result;
@@ -437,8 +440,8 @@ static object _Cyc_write(object x, FILE *port)
 {object tmp = nil;
  object has_cycle = boolean_f;
  int i = 0;
- if (nullp(x)) {fprintf(port, "()"); return x;}
- if (obj_is_char(x)) {fprintf(port, "#\\%c", obj_obj2char(x)); return x;}
+ if (nullp(x)) {fprintf(port, "()"); return quote_void;}
+ if (obj_is_char(x)) {fprintf(port, "#\\%c", obj_obj2char(x)); return quote_void;}
  switch (type_of(x))
    {case string_tag:
       fprintf(port, "\"%s\"", ((string_type *) x)->str);
@@ -476,7 +479,7 @@ static object _Cyc_write(object x, FILE *port)
       break;
     default:
       Cyc_display(x, port);}
- return x;}
+ return quote_void;}
 
 object Cyc_write(object x, FILE *port)
 {object y = _Cyc_write(x, port);
@@ -486,11 +489,11 @@ object Cyc_write(object x, FILE *port)
 object Cyc_write_char(object c, object port) 
 {
   if (obj_is_char(c)) {
-    fprintf(((port_type *)port)->fp, "%c", obj_obj2char(c)); return c;
+    fprintf(((port_type *)port)->fp, "%c", obj_obj2char(c));
   } else {
     Cyc_rt_raise2("Argument is not a character", c);
   }
-  return c;
+  return quote_void;
 }
 
 /* Some of these non-consing functions have been optimized from CPS. */
diff --git a/runtime.h b/runtime.h
index 21a92634..cb5fd961 100644
--- a/runtime.h
+++ b/runtime.h
@@ -224,6 +224,7 @@ extern jmp_buf jmp_main; /* Where to jump to. */
 extern const object boolean_t;
 extern const object boolean_f;
 extern const object quote_Cyc_191procedure;
+extern const object quote_void;
 
 /* This section is auto-generated via --autogen */
 extern const object primitive_Cyc_91global_91vars;