add (if cond if-true if-false) builtin

1 files changed, 45 insertions, 10 deletions

diff --git a/com.c b/com.c
index 3d891f7..fef2dab 100644
--- a/com.c
+++ b/com.c
@@ -7,6 +7,19 @@
 #include "read.h"
 #include "state.h"
 
+static size_t placeholder(State *S, Chunk *ch) {
+	size_t old_ix = ch->bc.len;
+	chunk_wbc(S, ch, 0x00);
+	chunk_wbc(S, ch, 0x00);
+	return old_ix;
+}
+
+static void patch(State *S, Chunk *ch, size_t addr, uint16_t val) {
+	ch->bc.d[addr] = val & 0xff;
+	ch->bc.d[addr+1] = (val & 0xff00) >> 8;
+}
+
+
 static void compile_node(State *S, Chunk *ch, AstNode a) {
 	switch (a.ty) {
 	case AST_IDENT:;
@@ -17,8 +30,7 @@ static void compile_node(State *S, Chunk *ch, AstNode a) {
 		else if (0 == strcmp(ident, "nil")) chunk_wbc(S, ch, OP_NIL);
 		else {
 			// global read
-			size_t len = strlen(a.as.str);
-			ObjString *o = objstring_copy(S, a.as.str, len);
+			ObjString *o = objstring_copy_cstr(S, a.as.str);
 			chunk_wbc(S, ch, OP_GETGLOBAL);
 			chunk_wbc(S, ch, chunk_wconst(S, ch, VAL_OBJ(o)));
 		}
@@ -28,8 +40,7 @@ static void compile_node(State *S, Chunk *ch, AstNode a) {
 		chunk_wbc(S, ch, chunk_wconst(S, ch, VAL_NUM(a.as.num)));
 		break;
 	case AST_STRING: {
-		size_t len = strlen(a.as.str);
-		ObjString *o = objstring_copy(S, a.as.str, len);
+		ObjString *o = objstring_copy_cstr(S, a.as.str);
 		chunk_wbc(S, ch, OP_LOADK);
 		chunk_wbc(S, ch, chunk_wconst(S, ch, VAL_OBJ(o)));
 		break;
@@ -37,29 +48,53 @@ static void compile_node(State *S, Chunk *ch, AstNode a) {
 	case AST_LIST: {
 		AstVec l = a.as.list;
 		#define CK(cond, msg) if (!(cond)) { puts(msg); exit(1); }
+		CK(l.len > 0, "can't handle empty list");
 		CK(l.vals[0].ty == AST_IDENT, "can only call ops");
 
-		if (0 == strcmp(l.vals[0].as.str, "print")) {
+		char *name = l.vals[0].as.str;
+
+		if (0 == strcmp(name, "print")) {
 			CK(l.len == 2, "print requires exactly 1 argument");
 			compile_node(S, ch, l.vals[1]);
 			chunk_wbc(S, ch, OP_PRINT);
-		} else if (0 == strcmp(l.vals[0].as.str, "set")) {
+		} else if (0 == strcmp(name, "set")) {
 			CK(l.len == 3, "set requires exactly 2 arguments");
 			AstNode ident = l.vals[1];
 			CK(ident.ty == AST_IDENT, "set's first argument must be identifier");
 
-			size_t len = strlen(ident.as.str);
-			ObjString *o = objstring_copy(S, ident.as.str, len);
-
+			ObjString *o = objstring_copy_cstr(S, ident.as.str);
 			compile_node(S, ch, l.vals[2]);
 			chunk_wbc(S, ch, OP_SETGLOBAL);
 			chunk_wbc(S, ch, chunk_wconst(S, ch, VAL_OBJ(o)));
-		} else if (0 == strcmp(l.vals[0].as.str, "do")) {
+		} else if (0 == strcmp(name, "do")) {
 			for (int i = 1; i < l.len - 1; i++) {
 				compile_node(S, ch, l.vals[i]);
 				chunk_wbc(S, ch, OP_DROP);
 			}
 			compile_node(S, ch, l.vals[l.len - 1]);
+		} else if (0 == strcmp(name, "if")) {
+			CK(l.len == 4, "if requires exactly 3 arguments");
+			// (if cond if-true if-false)
+			// cond
+			// 0branch ->A
+			// if-true
+			// skip ->B
+			// A: if-false
+			// B:
+			compile_node(S, ch, l.vals[1]);
+			chunk_wbc(S, ch, OP_0BRANCH);
+			size_t ph1 = placeholder(S, ch);
+			compile_node(S, ch, l.vals[2]);
+			chunk_wbc(S, ch, OP_SKIP);
+			size_t ph2 = placeholder(S, ch);
+			size_t dest1 = ch->bc.len;
+			compile_node(S, ch, l.vals[3]);
+			size_t dest2 = ch->bc.len;
+
+			patch(S, ch, ph1, dest1 - ph1 - 2);
+			patch(S, ch, ph2, dest2 - ph2 - 2);
+
+
 		} else {
 				
 			CK(l.len == 3, "can only compile binary ops");