add when form

1 files changed, 19 insertions, 6 deletions

diff --git a/com.c b/com.c
index 862d26f..e14bbc6 100644
--- a/com.c
+++ b/com.c
@@ -270,6 +270,24 @@ static void if_form(Compiler *C, ObjArr *a, Op _, int flags) {
 	CHECK(stack_cur_a == orig_stack_cur + 1, "this should never happen");
 }
 
+static void when_form(Compiler *C, ObjArr *a, Op _, int flags) {
+	// (when cond body...)
+	// cond
+	// 0branch -> A
+	// body...
+	// drop
+	// A:
+	// nil
+	cpl_expr(C, a->d[1], 0);
+	cpl_op(C, OP_0BRANCH);
+	size_t ph = placeholder(C);
+	cpl_body(C, a, 2, 0);
+	cpl_op(C, OP_DROP);
+	size_t dest = BYTECODE(C).len;
+	patch(C, ph, dest - ph - 2);
+	cpl_op(C, OP_NIL);
+}
+
 static void while_form(Compiler *C, ObjArr *a, Op _, int flags) {
 	// (while cond body ...)
 	// A:
@@ -576,6 +594,7 @@ static BuiltinForm builtin_forms[] = {
 	{ "set!",    2, false, set_form, 0 },
 	{ "do",      1,  true, do_form, 0 },
 	{ "if",      3, false, if_form, 0 },
+	{ "when",    2,  true, when_form, 0 },
 	{ "while",   2,  true, while_form, 0 },
 	{ "for",     2,  true, for_form, 0 },
 	{ "each",    2,  true, each_form, 0 },
@@ -670,12 +689,6 @@ static void cpl_expr(Compiler *C, Val v, int flags) {
 	      "local declared not at top level (compiler bug)");
 }
 
-
-		
-
-
-
-
 static char buf[8193];
 
 int main(int argc, char **argv) {