From aa94396e5121d1afa465e0030ec1e62b6579de96 Mon Sep 17 00:00:00 2001
From: Luna <git@l4.pm>
Date: Sun, 2 Jun 2019 18:11:23 -0300
Subject: [PATCH] compiler: add nicer error handling

 - vm: fix pop opcode handler
---
 src/compiler.zig | 16 ++++++++++++++++
 src/vm.zig       |  5 ++++-
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/src/compiler.zig b/src/compiler.zig
index c6bdd5b..71750da 100644
--- a/src/compiler.zig
+++ b/src/compiler.zig
@@ -337,8 +337,24 @@ pub const Compiler = struct {
         try self.emitByte(OpCode.Pop);
     }
 
+    fn synchronize(self: *Compiler) !void {
+        self.parser.panicMode = false;
+
+        while (self.parser.current.ttype != .EOF) {
+            if (self.parser.previous.ttype == .SEMICOLON) return;
+
+            switch (self.parser.current.ttype) {
+                .CLASS, .FUN, .VAR, .FOR, .IF, .WHILE, .PRINT, .RETURN => return,
+                else => {},
+            }
+
+            try self.advance();
+        }
+    }
+
     fn declaration(self: *Compiler) !void {
         try self.statement();
+        if (self.parser.panicMode) try self.synchronize();
     }
 
     fn statement(self: *Compiler) !void {
diff --git a/src/vm.zig b/src/vm.zig
index 6ffc733..98211c6 100644
--- a/src/vm.zig
+++ b/src/vm.zig
@@ -255,7 +255,10 @@ pub const VM = struct {
                 chunk.OpCode.True => try self.push(values.BoolVal(true)),
                 chunk.OpCode.False => try self.push(values.BoolVal(false)),
 
-                chunk.OpCode.Pop => self.pop(),
+                chunk.OpCode.Pop => blk: {
+                    _ = self.pop();
+                    break :blk;
+                },
 
                 chunk.OpCode.Equal => blk: {
                     var a = self.pop();