syntax "cond"

src/eval.c

@@ -38,6 +38,9 @@ struct Object *eval(
         if (strcmp(func_expr->s, "begin") == 0) {
             return syntax_begin(args, environment);
         }
+        if (strcmp(func_expr->s, "cond") == 0) {
+            return syntax_cond(args, environment);
+        }
         if (strcmp(func_expr->s, "define") == 0) {
             return syntax_define(args, environment);
         }

src/syntax.c

@@ -4,6 +4,7 @@
 #include "object.h"
 
 #include <assert.h>
+#include <string.h>
 
 /*******************************************
  * Special syntax to use in the executable *
@@ -41,6 +42,47 @@ struct Object *syntax_begin(
     return result;
 }
 
+struct Object *syntax_cond(
+    struct Object *const args,
+    struct Object *const environment
+) {
+    assert(Object_is_pair(environment));
+    assert(OBJECT_IS_LIST_HEAD(environment->pair.cdr));
+    assert(OBJECT_IS_LIST_HEAD(environment->pair.car));
+
+    assert(OBJECT_IS_LIST_HEAD(args));
+
+    for (struct Object *arg = args; !OBJECT_IS_NULL(arg); arg = arg->pair.cdr)
+    {
+        assert(Object_is_pair(arg));
+        assert(Object_is_pair(arg->pair.car));
+        assert(Object_is_pair(arg->pair.car->pair.cdr));
+        assert(OBJECT_IS_NULL(arg->pair.car->pair.cdr->pair.cdr));
+
+        struct Object *const cond_prog = arg->pair.car->pair.car;
+
+        if (Object_is_symbol(cond_prog) && strcmp(cond_prog->s, "else") == 0) {
+            assert(OBJECT_IS_NULL(arg->pair.cdr));
+        }
+    }
+
+    for (struct Object *arg = args; !OBJECT_IS_NULL(arg); arg = arg->pair.cdr)
+    {
+        struct Object *const cond_prog = arg->pair.car->pair.car;
+        struct Object *const val_prog  = arg->pair.car->pair.cdr->pair.car;
+
+        if (Object_is_symbol(cond_prog) && strcmp(cond_prog->s, "else") == 0) {
+            return eval(val_prog, environment);
+        }
+
+        if (!Object_is_false(eval(cond_prog, environment))) {
+            return eval(val_prog, environment);
+        }
+    }
+
+    return NULL;
+}
+
 struct Object *syntax_define(
     struct Object *const args,
     struct Object *const environment

src/syntax.h

@@ -15,6 +15,7 @@ struct Object *syntax_script(struct Object *args, struct Object *environment);
  *******************/
 
 struct Object *syntax_begin(struct Object *args, struct Object *environment);
+struct Object *syntax_cond(struct Object *args, struct Object *environment);
 struct Object *syntax_define(struct Object *args, struct Object *environment);
 struct Object *syntax_if(struct Object *args, struct Object *environment);
 struct Object *syntax_lambda(struct Object *args, struct Object *environment);

tests/syntax.scm

@@ -4,6 +4,17 @@
 (assert-equal 456 (begin 123 456))
 (assert-equal 789 (begin 123 456 789))
 
+;;; cond ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+(assert-equal '() (cond))
+(assert-equal '() (cond (#false 123)))
+(assert-equal 123 (cond (#true  123)))
+(assert-equal '() (cond (#false 123) (#false 456)))
+(assert-equal 123 (cond (#true  123) (#true  456)))
+(assert-equal 456 (cond (#false 123) (#true  456)))
+(assert-equal 123 (cond (#true  123) (#true  456) (else 789)))
+(assert-equal 456 (cond (#false 123) (#true  456) (else 789)))
+(assert-equal 789 (cond (#false 123) (#false 456) (else 789)))
+
 ;;; define ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 (assert-equal
   '(123 579)