Add: yield

Author: codybartfast

.vscode/tasks.json

@@ -36,7 +36,7 @@
                 "src/storage.c",
                 "src/strbldr.c",
                 //
-                "-O1", // Optimization Level. Tail Call Optimization seem to need >= 2
+                "-O3", // Optimization Level. Tail Call Optimization seem to need >= 2
                 "-std=c17", // 'ISO C 2017' standard
                 "-o",
                 "${workspaceFolder}/bin/sicp", // output e.g., "${fileDirname}/sicp",
@@ -76,4 +76,4 @@
             ],
         },
     ]
-}
+}

src/eceval.c

@@ -3,7 +3,9 @@
 
 #include "eceval.h"
 
+#include <stdbool.h>
 #include <stdlib.h>
+
 #include "error.h"
 #include "list.h"
 #include "mceval.h"
@@ -81,7 +83,7 @@ static void set_proc_name(struct core *cr)
 					  of_string("<unknown>");
 }
 
-static obj ecevalgoto(struct core *cr)
+static obj ecevalgoto(struct core *cr, bool yield)
 {
 	obj go_obj = restore(cr);
 	goto go_obj;
@@ -422,6 +424,10 @@ static obj ecevalgoto(struct core *cr)
 	return error_eval(AREA, "Unknown procedure type: %s", errstr(cr->proc));
 
 go_cont:
+	if (yield) {
+		save(cr->cont, cr);
+		return yielded;
+	}
 	go_obj = cr->cont;
 go_obj:
 	if (is_eq(go_obj, ev_return_caller))
@@ -456,10 +462,14 @@ static obj ecevalgoto(struct core *cr)
 
 obj eceval(obj expression, obj _environment)
 {
+	obj rslt;
+
 	struct core *cr = dfltcore();
 	cr->expr = expression;
 	cr->env = _environment;
 	cr->cont = ev_return_caller;
 	save_nogc(ev_eval_dispatch, cr);
-	return ecevalgoto(cr);
+	while (is_yielded(rslt = ecevalgoto(cr, false)))
+		;
+	return rslt;
 }

src/obj.c

@@ -302,6 +302,11 @@ bool is_void(obj dat)
 	return type(dat) == TYPE_VOID;
 }
 const obj void_o = OBJ_2(TYPE_VOID, SUBTYPE_NOT_SET);
+const obj yielded = OBJ_2(TYPE_YIELDED, SUBTYPE_NOT_SET);
+bool is_yielded(obj dat)
+{
+	return type(dat) == TYPE_YIELDED;
+}
 
 // BROKEN HEART
 

src/obj.h

@@ -29,7 +29,8 @@ enum type {
 	TYPE_BROKEN_HEART, // 11
 	TYPE_BITMAP, // 12
 	TYPE_UNASSIGNED, // 13
-	TYPE_ERROR // 14
+	TYPE_YIELDED, // 14
+	TYPE_ERROR // 15
 };
 
 enum { SUBTYPE_NOT_SET = 0 };
@@ -172,6 +173,8 @@ extern const obj ok;
 extern const obj unspecified;
 bool is_void(obj dat);
 extern const obj void_o;
+extern const obj yielded;
+bool is_yielded(obj dat);
 
 // BROKEN HEART