compiler: finish parser (for math expressions)

src/compiler.zig

@@ -13,7 +13,8 @@ const TokenType = tokens.TokenType;
 const Value = values.Value;
 const OpCode = chunks.OpCode;
 
-pub const Parser = struct {
+/// Holds parser state for the compiler.
+const Parser = struct {
     previous: Token = undefined,
     current: Token = undefined,
 
@@ -22,6 +23,93 @@ pub const Parser = struct {
     panicMode: bool = false,
 };
 
+/// Represents the order of operations in the parser.
+const Precedence = enum(u5) {
+    None,
+    Assignment, // =
+    Or, // or
+    And, // and
+    Equality, // == !=
+    Comparison, // < > <= >=
+    Term, // + -
+    Factor, // * /
+    Unary, // ! -
+    Call, // . () []
+    Primary,
+};
+
+const ParseFn = fn (*Compiler) anyerror!void;
+
+const ParseRule = struct {
+    prefix: ?ParseFn = null,
+    infix: ?ParseFn = null,
+    precedence: Precedence = Precedence.None,
+};
+
+/// For each token, this defines a parse rule for it.
+var rules = []ParseRule{
+    // for LEFT_PAREN, we determine it as a call precedence
+    // plus a prefix parse function of grouping
+    ParseRule{ .prefix = Compiler.grouping, .precedence = .Call },
+    ParseRule{},
+    ParseRule{},
+    ParseRule{},
+    ParseRule{},
+
+    // dot token, means a call too, for things like a.b
+    ParseRule{ .precedence = .Call },
+
+    // specific to -, as it can be an unary operator when its a prefix
+    // of something, or a binary one, when its a infix or another thing.
+    ParseRule{
+        .prefix = Compiler.unary,
+        .infix = Compiler.binary,
+        .precedence = .Term,
+    },
+
+    ParseRule{ .infix = Compiler.binary, .precedence = .Term },
+    ParseRule{},
+
+    // slash is a binary operator, as well as star.
+    ParseRule{ .infix = Compiler.binary, .precedence = .Factor },
+    ParseRule{ .infix = Compiler.binary, .precedence = .Factor },
+
+    // as the token enum says, those are 1/2 char tokens.
+    ParseRule{},
+    // this is specifically for the != operator
+    ParseRule{ .precedence = .Equality },
+    ParseRule{},
+    // this is specifically for the == operator
+    ParseRule{ .precedence = .Equality },
+
+    // all the comparison ones
+    ParseRule{ .precedence = .Comparison },
+    ParseRule{ .precedence = .Comparison },
+    ParseRule{ .precedence = .Comparison },
+    ParseRule{ .precedence = .Comparison },
+
+    ParseRule{},
+    ParseRule{},
+    ParseRule{ .prefix = Compiler.number },
+    ParseRule{ .precedence = .And },
+    ParseRule{},
+    ParseRule{},
+    ParseRule{},
+    ParseRule{},
+    ParseRule{},
+    ParseRule{},
+    ParseRule{},
+    ParseRule{ .precedence = .Or },
+    ParseRule{},
+    ParseRule{},
+    ParseRule{},
+    ParseRule{},
+    ParseRule{},
+    ParseRule{},
+    ParseRule{},
+    ParseRule{},
+};
+
 pub const Compiler = struct {
     src: []const u8,
     stdout: vm.StdOut,
@@ -29,12 +117,14 @@ pub const Compiler = struct {
     parser: Parser,
     scanr: Scanner = undefined,
     chunk: *chunks.Chunk,
+    debug_flag: bool = false,
 
     pub fn init(
         allocator: *Allocator,
         chunk: *chunks.Chunk,
         stdout: vm.StdOut,
         source: []const u8,
+        debug_flag: bool,
     ) Compiler {
         return Compiler{
             .src = source,
@@ -42,6 +132,7 @@ pub const Compiler = struct {
             .allocator = allocator,
             .stdout = stdout,
             .parser = Parser{},
+            .debug_flag = debug_flag,
         };
     }
 
@@ -117,6 +208,10 @@ pub const Compiler = struct {
 
     fn end(self: *Compiler) !void {
         try self.emitReturn();
+
+        if (self.debug_flag and !self.parser.hadError) {
+            try self.currentChunk().disassemble(self.stdout, "code");
+        }
     }
 
     fn grouping(self: *Compiler) !void {
@@ -126,21 +221,66 @@ pub const Compiler = struct {
 
     /// Emits bytecode for a number being loaded into the code.
     fn number(self: *Compiler) !void {
-        var value: f64 = try std.fmt.parseFloat(f64, parser.previous.lexeme);
+        var value: f64 = try std.fmt.parseFloat(
+            f64,
+            self.parser.previous.lexeme,
+        );
         try self.emitConstant(value);
     }
 
     /// Emits bytecode for a given unary.
     fn unary(self: *Compiler) !void {
         var ttype = self.parser.previous.ttype;
-        try self.expression();
+        try self.parsePrecedence(.Unary);
+
         switch (ttype) {
             .MINUS => try self.emitByte(OpCode.Negate),
             else => unreachable,
         }
     }
 
-    fn expression(self: *Compiler) !void {}
+    fn binary(self: *Compiler) !void {
+        var op_type = self.parser.previous.ttype;
+        var rule: *ParseRule = self.getRule(op_type);
+        try self.parsePrecedence(@intToEnum(Precedence, @enumToInt(rule.precedence) + 1));
+
+        switch (op_type) {
+            .PLUS => try self.emitByte(OpCode.Add),
+            .MINUS => try self.emitByte(OpCode.Subtract),
+            .STAR => try self.emitByte(OpCode.Multiply),
+            .SLASH => try self.emitByte(OpCode.Divide),
+            else => unreachable,
+        }
+    }
+
+    fn parsePrecedence(self: *Compiler, precedence: Precedence) !void {
+        try self.advance();
+        var as_int = @enumToInt(precedence);
+        var prefix_rule_opt = self.getRule(self.parser.previous.ttype).prefix;
+
+        if (prefix_rule_opt) |prefix_rule| {
+            try prefix_rule(self);
+
+            while (as_int <= @enumToInt(self.getRule(self.parser.current.ttype).precedence)) {
+                try self.advance();
+                var infix_rule_opt = self.getRule(self.parser.previous.ttype).infix;
+                if (infix_rule_opt) |infix_rule| {
+                    try infix_rule(self);
+                }
+            }
+        } else {
+            self.errorPrevious("Expect expression.");
+            return;
+        }
+    }
+
+    fn getRule(self: *Compiler, ttype: TokenType) *ParseRule {
+        return &rules[@enumToInt(ttype)];
+    }
+
+    fn expression(self: *Compiler) !void {
+        try self.parsePrecedence(.Assignment);
+    }
 
     /// Compile the source given when initializing the compiler
     /// into the given chunk.
@@ -148,7 +288,7 @@ pub const Compiler = struct {
         self.scanr = try scanner.Scanner.init(self.allocator, self.src);
 
         try self.advance();
-        //try self.expression();
+        try self.expression();
         try self.consume(.EOF, "Expect end of expression.");
         try self.end();
 

src/vm.zig

@@ -167,7 +167,13 @@ pub const VM = struct {
         //return res;
         var chk = try Chunk.init(self.allocator);
 
-        var cmpr = Compiler.init(self.allocator, &chk, self.stdout, self.src);
+        var cmpr = Compiler.init(
+            self.allocator,
+            &chk,
+            self.stdout,
+            self.src,
+            self.debug_flag,
+        );
         if (!try cmpr.compile(&chk)) {
             return InterpretResult.CompileError;
         }