move towards dynamically typed values

- remove InterpretResult as an enum, replace by error.
 - scanner: fix peekNext()
 - vm: add runtime errors, add VM.peek()

src/compiler.zig

@@ -167,8 +167,6 @@ pub const Compiler = struct {
             if (token_opt) |token| {
                 self.parser.current = token;
                 break;
-            } else {
-                self.errorCurrent(self.parser.current.lexeme);
             }
         }
     }
@@ -221,11 +219,12 @@ pub const Compiler = struct {
 
     /// Emits bytecode for a number being loaded into the code.
     fn number(self: *Compiler) !void {
+        std.debug.warn("parsing number: '{}'\n", self.parser.previous.lexeme);
         var value: f64 = try std.fmt.parseFloat(
             f64,
             self.parser.previous.lexeme,
         );
-        try self.emitConstant(value);
+        try self.emitConstant(values.NumberVal(value));
     }
 
     /// Emits bytecode for a given unary.

src/main.zig

@@ -12,12 +12,12 @@ const InterpretResult = vm.InterpretResult;
 
 pub var hadError = false;
 
-fn run(allocator: *Allocator, data: []u8) !InterpretResult {
+fn run(allocator: *Allocator, data: []u8) !void {
     var stdout_file = try std.io.getStdOut();
     const stdout = &stdout_file.outStream().stream;
 
     var vmach = try vm.VM.init(allocator, stdout, data, true);
-    return try vmach.interpret();
+    try vmach.interpret();
 }
 
 pub fn doError(line: usize, message: []const u8) !void {
@@ -40,9 +40,14 @@ fn runFile(allocator: *Allocator, path: []const u8) !void {
     var slice = try allocator.alloc(u8, total_bytes);
     _ = try lox_file.read(slice);
 
-    var res = try run(allocator, slice);
-    if (res == vm.InterpretResult.CompileError) std.os.exit(65);
-    if (res == vm.InterpretResult.RuntimeError) std.os.exit(70);
+    run(allocator, slice) catch |err| {
+        switch (err) {
+            InterpretResult.Ok => {},
+            InterpretResult.CompileError => std.os.exit(65),
+            InterpretResult.RuntimeError => std.os.exit(70),
+            else => return err,
+        }
+    };
 }
 
 fn runPrompt(allocator: *Allocator) !void {
@@ -59,7 +64,15 @@ fn runPrompt(allocator: *Allocator) !void {
             return err;
         };
 
-        _ = try run(allocator, line);
+        run(allocator, line) catch |err| {
+            switch (err) {
+                InterpretResult.Ok => {},
+                InterpretResult.CompileError, InterpretResult.RuntimeError => blk: {
+                    try stdout.print("compile/runtime error.\n");
+                },
+                else => return err,
+            }
+        };
     }
 }
 

src/new_scanner.zig

@@ -147,8 +147,8 @@ pub const Scanner = struct {
     }
 
     fn peekNext(self: *Scanner) u8 {
-        if (self.isAtEnd()) return 0;
-        return self.source[self.current - 1];
+        if (self.current + 1 >= self.source.len) return 0;
+        return self.source[self.current + 1];
     }
 
     fn skipWhitespace(self: *Scanner) void {
@@ -255,10 +255,12 @@ pub const Scanner = struct {
             '>' => self.makeMatchToken('=', .GREATER_EQUAL, .GREATER),
 
             '/' => blk: {
+                std.debug.warn("next: {}\n", self.peekNext());
                 if (self.peekNext() == '/') {
                     while (self.peek() != '\n' and !self.isAtEnd()) {
                         _ = self.advance();
                     }
+
                     break :blk null;
                 } else {
                     break :blk self.makeToken(.SLASH);

src/value.zig

@@ -3,10 +3,42 @@ const std = @import("std");
 const Allocator = std.mem.Allocator;
 
 // NOTE: right now, only numbers.
-pub const Value = f64;
+
+pub const ValueType = enum(u8) {
+    Bool,
+    Nil,
+    Number,
+};
+
+pub const ValueValue = union(ValueType) {
+    Bool: bool,
+    Nil: void,
+    Number: f64,
+};
+
+pub const Value = struct {
+    vtype: ValueType,
+    as: ValueValue,
+};
+
+// helper functions
+pub fn BoolVal(val: bool) Value {
+    return Value{ .vtype = .Bool, .as = ValueValue{ .Bool = val } };
+}
+
+pub fn NilVal() Value {
+    return Value{ .vtype = .Nil, .as = ValueValue{ .Nil = {} } };
+}
+
+pub fn NumberVal(val: f64) Value {
+    return Value{ .vtype = .Number, .as = ValueValue{ .Number = val } };
+}
 
 pub fn printValue(stdout: var, value: Value) !void {
-    try stdout.print("{}", value);
+    switch (value.as) {
+        .Number => try stdout.print("{}", value.as.Number),
+        else => unreachable,
+    }
 }
 
 pub const ValueList = struct {

src/vm.zig

@@ -1,6 +1,7 @@
 const std = @import("std");
 const chunk = @import("chunk.zig");
 const value = @import("value.zig");
+const values = value;
 const compiler = @import("compiler.zig");
 
 const Chunk = chunk.Chunk;
@@ -9,7 +10,7 @@ const Compiler = compiler.Compiler;
 
 pub const StdOut = *std.io.OutStream(std.fs.File.WriteError);
 
-pub const InterpretResult = enum {
+pub const InterpretResult = error{
     Ok,
     CompileError,
     RuntimeError,
@@ -91,35 +92,50 @@ pub const VM = struct {
     }
 
     /// gets a f64 out of a value on the top of the stack.
-    fn popNum(self: *VM) f64 {
-        return self.pop();
+    fn popNum(self: *VM) !f64 {
+        var val: Value = self.pop();
+
+        switch (val.vtype) {
+            .Number => return val.as.Number,
+
+            else => |vtype| blk: {
+                self.runtimeError("Expected number, got {x}", vtype);
+                return InterpretResult.RuntimeError;
+            },
+        }
     }
 
     fn doAdd(self: *VM) !void {
-        var b = self.popNum();
-        var a = self.popNum();
-        try self.push(a + b);
+        var b = try self.popNum();
+        var a = try self.popNum();
+        try self.push(values.NumberVal(a + b));
     }
 
     fn doSub(self: *VM) !void {
-        var b = self.popNum();
-        var a = self.popNum();
-        try self.push(a * b);
+        var b = try self.popNum();
+        var a = try self.popNum();
+        try self.push(values.NumberVal(a - b));
     }
 
     fn doMul(self: *VM) !void {
-        var b = self.popNum();
-        var a = self.popNum();
-        try self.push(a * b);
+        var b = try self.popNum();
+        var a = try self.popNum();
+        try self.push(values.NumberVal(a * b));
     }
 
     fn doDiv(self: *VM) !void {
-        var b = self.popNum();
-        var a = self.popNum();
-        try self.push(a / b);
+        var b = try self.popNum();
+        var a = try self.popNum();
+        try self.push(values.NumberVal(a / b));
     }
 
-    fn run(self: *VM) !InterpretResult {
+    fn runtimeError(self: *VM, comptime fmt: []const u8, args: ...) void {
+        std.debug.warn(fmt, args);
+        std.debug.warn("\n[line {}] in script\n", self.chk.lines[self.ip]);
+        self.resetStack();
+    }
+
+    fn run(self: *VM) !void {
         while (true) {
             if (self.debug_flag) {
                 try self.debugStack();
@@ -150,7 +166,22 @@ pub const VM = struct {
                 chunk.OpCode.Subtract => try self.doSub(),
                 chunk.OpCode.Multiply => try self.doMul(),
                 chunk.OpCode.Divide => try self.doDiv(),
-                chunk.OpCode.Negate => try self.push(-self.pop()),
+                chunk.OpCode.Negate => blk: {
+                    var val = self.peek(0);
+                    if (val.vtype != .Bool) {
+                        self.runtimeError("Operand must be a number.");
+                        return InterpretResult.RuntimeError;
+                    }
+
+                    val = self.pop();
+                    switch (val.as) {
+                        .Number => |num| {
+                            try self.push(values.NumberVal(-num));
+                        },
+                        else => unreachable,
+                    }
+                },
+
                 else => blk: {
                     std.debug.warn("Unknown instruction: {x}\n", instruction);
                     return InterpretResult.RuntimeError;
@@ -159,7 +190,7 @@ pub const VM = struct {
         }
     }
 
-    pub fn interpret(self: *VM) !InterpretResult {
+    pub fn interpret(self: *VM) !void {
         //self.ip = 0;
         //self.debug("VM start\n");
         //var res = try self.run();
@@ -196,4 +227,8 @@ pub const VM = struct {
         self.stackTop -= 1;
         return self.stack[self.stackTop];
     }
+
+    pub fn peek(self: *VM, distance: usize) Value {
+        return self.stack[self.stackTop - 1 - distance];
+    }
 };