add expression statements

src/chunk.zig

@@ -27,6 +27,7 @@ const AllOpcodes = struct {
     pub Less: u8 = 14,
 
     pub Print: u8 = 15,
+    pub Pop: u8 = 16,
 };
 
 pub const OpCode = AllOpcodes{};
@@ -193,6 +194,8 @@ pub const Chunk = struct {
             return try simpleInstruction(stdout, "OP_LESS", index);
         } else if (instruction == OpCode.Print) {
             return try simpleInstruction(stdout, "OP_PRINT", index);
+        } else if (instruction == OpCode.Pop) {
+            return try simpleInstruction(stdout, "OP_POP", index);
         } else {
             try stdout.print("Unknown opcode: {}\n", instruction);
             return index + 1;

src/compiler.zig

@@ -331,6 +331,12 @@ pub const Compiler = struct {
         try self.emitByte(OpCode.Print);
     }
 
+    fn exprStmt(self: *Compiler) !void {
+        try self.expression();
+        try self.consume(.SEMICOLON, "Expect ';' after expression.");
+        try self.emitByte(OpCode.Pop);
+    }
+
     fn declaration(self: *Compiler) !void {
         try self.statement();
     }
@@ -338,6 +344,8 @@ pub const Compiler = struct {
     fn statement(self: *Compiler) !void {
         if (try self.match(.PRINT)) {
             try self.printStmt();
+        } else {
+            try self.exprStmt();
         }
     }
 

src/vm.zig

@@ -255,6 +255,8 @@ 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.Equal => blk: {
                     var a = self.pop();
                     var b = self.pop();