add support for nil, true and false literal values

src/chunk.zig

@@ -13,6 +13,11 @@ const AllOpcodes = struct {
     pub Multiply: u8 = 5,
     pub Divide: u8 = 6,
     pub Negate: u8 = 7,
+
+    // basic type op codes
+    pub Nil: u8 = 8,
+    pub True: u8 = 9,
+    pub False: u8 = 10,
 };
 
 pub const OpCode = AllOpcodes{};
@@ -163,6 +168,12 @@ pub const Chunk = struct {
             return try simpleInstruction(stdout, "OP_MULTIPLY", index);
         } else if (instruction == OpCode.Divide) {
             return try simpleInstruction(stdout, "OP_DIVIDE", index);
+        } else if (instruction == OpCode.Nil) {
+            return try simpleInstruction(stdout, "OP_NIL", index);
+        } else if (instruction == OpCode.True) {
+            return try simpleInstruction(stdout, "OP_TRUE", index);
+        } else if (instruction == OpCode.False) {
+            return try simpleInstruction(stdout, "OP_FALSE", index);
         } else {
             try stdout.print("Unknown opcode: {}\n", instruction);
             return index + 1;

src/compiler.zig

@@ -94,17 +94,19 @@ var rules = []ParseRule{
     ParseRule{ .precedence = .And },
     ParseRule{},
     ParseRule{},
+
+    // false
+    ParseRule{ .prefix = Compiler.literal },
     ParseRule{},
     ParseRule{},
     ParseRule{},
-    ParseRule{},
+    ParseRule{ .prefix = Compiler.literal },
-    ParseRule{},
     ParseRule{ .precedence = .Or },
     ParseRule{},
     ParseRule{},
     ParseRule{},
     ParseRule{},
-    ParseRule{},
+    ParseRule{ .prefix = Compiler.literal },
     ParseRule{},
     ParseRule{},
     ParseRule{},
@@ -252,6 +254,15 @@ pub const Compiler = struct {
         }
     }
 
+    fn literal(self: *Compiler) !void {
+        switch (self.parser.previous.ttype) {
+            .FALSE => try self.emitByte(OpCode.False),
+            .NIL => try self.emitByte(OpCode.Nil),
+            .TRUE => try self.emitByte(OpCode.True),
+            else => unreachable,
+        }
+    }
+
     fn parsePrecedence(self: *Compiler, precedence: Precedence) !void {
         try self.advance();
         var as_int = @enumToInt(precedence);

src/value.zig

@@ -36,6 +36,8 @@ pub fn NumberVal(val: f64) Value {
 
 pub fn printValue(stdout: var, value: Value) !void {
     switch (value.as) {
+        .Nil => try stdout.print("nil"),
+        .Bool => try stdout.print("{}", value.as.Bool),
         .Number => try stdout.print("{}", value.as.Number),
         else => unreachable,
     }

src/vm.zig

@@ -162,6 +162,10 @@ pub const VM = struct {
                     return InterpretResult.Ok;
                 },
 
+                chunk.OpCode.Nil => try self.push(values.NilVal()),
+                chunk.OpCode.True => try self.push(values.BoolVal(true)),
+                chunk.OpCode.False => try self.push(values.BoolVal(false)),
+
                 chunk.OpCode.Add => try self.doAdd(),
                 chunk.OpCode.Subtract => try self.doSub(),
                 chunk.OpCode.Multiply => try self.doMul(),