From ba6ab6759e4257e543ca5da4caf2705711e5b3ed Mon Sep 17 00:00:00 2001
From: Tom Willemse
Date: Wed, 12 Jan 2022 22:58:10 -0800
Subject: Chapter 23.2

---
 clox/src/compiler.c | 64 +++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 62 insertions(+), 2 deletions(-)

(limited to 'clox/src/compiler.c')

diff --git a/clox/src/compiler.c b/clox/src/compiler.c
index a964b79..d965f45 100644
--- a/clox/src/compiler.c
+++ b/clox/src/compiler.c
@@ -119,6 +119,13 @@ static void emitBytes(uint8_t byte1, uint8_t byte2) {
   emitByte(byte2);
 }
 
+static int emitJump(uint8_t instruction) {
+  emitByte(instruction);
+  emitByte(0xff);
+  emitByte(0xff);
+  return currentChunk()->count - 2;
+}
+
 static void emitReturn() { emitByte(OP_RETURN); }
 
 static uint8_t makeConstant(Value value) {
@@ -135,6 +142,18 @@ static void emitConstant(Value value) {
   emitBytes(OP_CONSTANT, makeConstant(value));
 }
 
+static void patchJump(int offset) {
+  // -2 to adjust for the bytecode for the jump offset itself...
+  int jump = currentChunk()->count - offset - 2;
+
+  if (jump > UINT16_MAX) {
+    error("Too much code to jump over.");
+  }
+
+  currentChunk()->code[offset] = (jump >> 8) & 0xff;
+  currentChunk()->code[offset + 1] = jump & 0xff;
+}
+
 static void initCompiler(Compiler *compiler) {
   compiler->localCount = 0;
   compiler->scopeDepth = 0;
@@ -258,6 +277,25 @@ static void expressionStatement() {
   emitByte(OP_POP);
 }
 
+static void ifStatement() {
+  consume(TOKEN_LEFT_PAREN, "Expect '(' after 'if'.");
+  expression();
+  consume(TOKEN_RIGHT_PAREN, "Expect ')' after condition.");
+
+  int thenJump = emitJump(OP_JUMP_IF_FALSE);
+  emitByte(OP_POP);
+  statement();
+
+  int elseJump = emitJump(OP_JUMP);
+
+  patchJump(thenJump);
+  emitByte(OP_POP);
+
+  if (match(TOKEN_ELSE))
+    statement();
+  patchJump(elseJump);
+}
+
 static void printStatement() {
   expression();
   consume(TOKEN_SEMICOLON, "Expect ';' after value.");
@@ -302,6 +340,8 @@ static void declaration() {
 static void statement() {
   if (match(TOKEN_PRINT)) {
     printStatement();
+  } else if (match(TOKEN_IF)) {
+    ifStatement();
   } else if (match(TOKEN_LEFT_BRACE)) {
     beginScope();
     block();
@@ -316,6 +356,26 @@ static void number(bool canAssign) {
   emitConstant(NUMBER_VAL(value));
 }
 
+static void and_(bool canAssign) {
+  int endJump = emitJump(OP_JUMP_IF_FALSE);
+
+  emitByte(OP_POP);
+  parsePrecedence(PREC_AND);
+
+  patchJump(endJump);
+}
+
+static void or_(bool canAssign) {
+  int elseJump = emitJump(OP_JUMP_IF_FALSE);
+  int endJump = emitJump(OP_JUMP);
+
+  patchJump(elseJump);
+  emitByte(OP_POP);
+
+  parsePrecedence(PREC_OR);
+  patchJump(endJump);
+}
+
 static void string(bool canAssign) {
   emitConstant(OBJ_VAL(
       copyString(parser.previous.start + 1, parser.previous.length - 2)));
@@ -393,7 +453,7 @@ ParseRule rules[] = {
     [TOKEN_IDENTIFIER] = {variable, NULL, PREC_NONE},
     [TOKEN_STRING] = {string, NULL, PREC_NONE},
     [TOKEN_NUMBER] = {number, NULL, PREC_NONE},
-    [TOKEN_AND] = {NULL, NULL, PREC_NONE},
+    [TOKEN_AND] = {NULL, and_, PREC_AND},
     [TOKEN_CLASS] = {NULL, NULL, PREC_NONE},
     [TOKEN_ELSE] = {NULL, NULL, PREC_NONE},
     [TOKEN_FALSE] = {literal, NULL, PREC_NONE},
@@ -401,7 +461,7 @@ ParseRule rules[] = {
     [TOKEN_FUN] = {NULL, NULL, PREC_NONE},
     [TOKEN_IF] = {NULL, NULL, PREC_NONE},
     [TOKEN_NIL] = {literal, NULL, PREC_NONE},
-    [TOKEN_OR] = {NULL, NULL, PREC_NONE},
+    [TOKEN_OR] = {NULL, or_, PREC_OR},
     [TOKEN_PRINT] = {NULL, NULL, PREC_NONE},
     [TOKEN_RETURN] = {NULL, NULL, PREC_NONE},
     [TOKEN_SUPER] = {NULL, NULL, PREC_NONE},
-- 
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