Add expression parser

.task/checksum/astgen

@@ -0,0 +1 @@
+5f28a0838ca9382a947da5bd52756cf3

Taskfile.yml

@@ -0,0 +1,44 @@
+# https://taskfile.dev
+
+version: '3'
+
+vars:
+  APP_NAME: golox
+
+tasks:
+  default:
+    cmds:
+      - task: run
+
+  run:
+    desc: "Run the interpreter"
+    deps: [build]
+    cmds:
+      - ./bin/{{.APP_NAME}} {{.CLI_ARGS}}
+
+  build:
+    desc: "Build the interpreter"
+    deps: [astgen]
+    cmds:
+      - go build -o bin/{{.APP_NAME}} cmd/golox/main.go
+
+  test:
+    desc: "Run tests"
+    deps: [astgen]
+    cmds:
+      - go test -v ./...
+
+  astgen:
+    desc: "Generate AST nodes"
+    cmds:
+      - go run cmd/astgen/main.go "./parser"
+    sources:
+      - cmd/astgen/main.go
+    generates:
+      - parser/expr.go
+
+  clean:
+    desc: "Clean up"
+    cmds:
+      - rm -rf bin/*
+

ast/printer.go

@@ -0,0 +1,50 @@
+package ast
+
+import (
+	"fmt"
+	"golox/parser"
+)
+
+type Printer struct {
+}
+
+func New() *Printer {
+	return &Printer{}
+}
+
+func (ap *Printer) Print(expr parser.Expr) string {
+	return expr.Accept(ap).(string)
+}
+
+func (ap *Printer) VisitBinaryExpr(expr *parser.BinaryExpr) any {
+	return ap.parenthesize(expr.Operator.Lexeme, expr.Left, expr.Right)
+}
+
+func (ap *Printer) VisitGroupingExpr(expr *parser.GroupingExpr) any {
+	return ap.parenthesize("group", expr.Expression)
+}
+
+func (ap *Printer) VisitLiteralExpr(expr *parser.LiteralExpr) any {
+	if expr.Value == nil {
+		return "nil"
+	}
+	return fmt.Sprint(expr.Value)
+}
+
+func (ap *Printer) VisitUnaryExpr(expr *parser.UnaryExpr) any {
+	return ap.parenthesize(expr.Operator.Lexeme, expr.Right)
+}
+
+func (ap *Printer) VisitErrorExpr(expr *parser.ErrorExpr) any {
+	return expr.Value
+}
+
+func (ap *Printer) parenthesize(name string, exprs ...parser.Expr) string {
+	str := "(" + name
+
+	for _, expr := range exprs {
+		str += " " + expr.Accept(ap).(string)
+	}
+
+	return str + ")"
+}

build.sh

@@ -1,2 +0,0 @@
-#!/bin/zsh
-go build -o bin/golox

cmd/astgen/main.go

@@ -0,0 +1,81 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"strings"
+)
+
+func main() {
+	if len(os.Args) != 2 {
+		fmt.Println("Usage: astgen <output_directory>")
+		os.Exit(64)
+	}
+
+	d := os.Args[1]
+
+	if _, err := os.Stat(d); os.IsNotExist(err) {
+		fmt.Println("Directory does not exist")
+		os.Exit(74)
+	}
+
+	fmt.Println("Generating AST classes in", d)
+
+	defineAst(d, "Expr", []string{
+		"Error    : Value string",
+		"Binary   : Left Expr, Operator token.Token, Right Expr",
+		"Grouping : Expression Expr",
+		"Literal  : Value any",
+		"Unary    : Operator token.Token, Right Expr",
+	})
+}
+
+func defineAst(outputDir, baseName string, types []string) {
+	path := outputDir + "/" + strings.ToLower(baseName) + ".go"
+
+	file, err := os.Create(path)
+	if err != nil {
+		fmt.Println("Error creating file", path)
+		os.Exit(74)
+	}
+	defer file.Close()
+
+	file.WriteString("package parser\n\n")
+	file.WriteString("import \"golox/token\"\n\n")
+	defineVisitor(file, baseName, types)
+
+	file.WriteString("type " + baseName + " interface {\n")
+	file.WriteString("	Accept(visitor " + baseName + "Visitor[any]) any\n")
+	file.WriteString("}\n\n")
+
+	for _, t := range types {
+		defineType(file, baseName, t)
+	}
+}
+
+func defineVisitor(file *os.File, baseName string, types []string) {
+	file.WriteString("type " + baseName + "Visitor[T any] interface {\n")
+
+	for _, t := range types {
+		typeName := strings.TrimSpace(t[:strings.Index(t, ":")-1])
+		file.WriteString("	Visit" + typeName + baseName + "(" + strings.ToLower(typeName) + " *" + typeName + baseName + ") T\n")
+	}
+
+	file.WriteString("}\n\n")
+}
+
+func defineType(file *os.File, baseName, typeString string) {
+	typeName := strings.TrimSpace(typeString[:strings.Index(typeString, ":")-1])
+	fields := strings.TrimSpace(typeString[strings.Index(typeString, ":")+1:])
+
+	file.WriteString("type " + typeName + baseName + " struct {\n")
+
+	for _, field := range strings.Split(fields, ", ") {
+		file.WriteString("	" + field + "\n")
+	}
+
+	file.WriteString("}\n\n")
+	file.WriteString("func (t *" + typeName + baseName + ") Accept(visitor " + baseName + "Visitor[any]) any {\n")
+	file.WriteString("	return visitor.Visit" + typeName + baseName + "(t)\n")
+	file.WriteString("}\n\n")
+}

cmd/golox/main.go

@@ -9,13 +9,14 @@ import (
 
 func main() {
 	nbArgs := len(os.Args)
+	l := lox.New()
 
 	if nbArgs > 2 {
 		fmt.Println("Usage: golox [script]")
 		os.Exit(64)
 	} else if nbArgs == 2 {
-		lox.RunFile(os.Args[1])
+		l.RunFile(os.Args[1])
 	} else {
-		lox.RunPrompt()
+		l.RunPrompt()
 	}
 }

errors/logger.go

@@ -0,0 +1,8 @@
+package errors
+
+import "golox/token"
+
+type Logger interface {
+	Error(line int, message string)
+	ErrorAtToken(t token.Token, message string)
+}

lox/lox.go

@@ -3,26 +3,36 @@ package lox
 import (
 	"bufio"
 	"fmt"
+	"golox/ast"
+	"golox/parser"
+	"golox/scanner"
+	"golox/token"
 	"os"
 )
 
-var hadError = false
+type Lox struct {
+	hadError bool
+}
+
+func New() *Lox {
+	return &Lox{hadError: false}
+}
 
-func RunFile(path string) {
+func (l *Lox) RunFile(path string) {
 	bytes, err := os.ReadFile(path)
 	if err != nil {
 		fmt.Println("Error reading file", path)
 		os.Exit(74)
 	}
 
-	run(string(bytes))
+	l.run(string(bytes))
 
-	if hadError {
+	if l.hadError {
 		os.Exit(65)
 	}
 }
 
-func RunPrompt() {
+func (l *Lox) RunPrompt() {
 	reader := bufio.NewReader(os.Stdin)
 
 	for {
@@ -38,19 +48,38 @@ func RunPrompt() {
 			break
 		}
 
-		run(line)
-		hadError = false
+		l.run(line)
+		l.hadError = false
 	}
 }
 
-func Error(line int, message string) {
-	report(line, "", message)
+func (l *Lox) Error(line int, message string) {
+	l.report(line, "", message)
 }
 
-func report(line int, where string, message string) {
+func (l *Lox) ErrorAtToken(t token.Token, message string) {
+	if t.Type == token.EOF {
+		l.report(t.Line, " at end", message)
+	} else {
+		l.report(t.Line, " at '"+t.Lexeme+"'", message)
+	}
+}
+
+func (l *Lox) report(line int, where string, message string) {
 	fmt.Printf("[line %d] Error %s: %s\n", line, where, message)
+	l.hadError = true
 }
 
-func run(source string) {
-	fmt.Println(source)
+func (l *Lox) run(source string) {
+	scanner := scanner.New(source, l)
+	tokens := scanner.ScanTokens()
+	parser := parser.New(tokens, l)
+	expr := parser.Parse()
+
+	if l.hadError {
+		return
+	}
+
+	p := ast.New()
+	fmt.Println(p.Print(expr))
 }

lox/lox_test.go

@@ -25,7 +25,8 @@ func TestRun(t *testing.T) {
 	}()
 
 	source := "print('Hello, World!');"
-	run(source)
+	l := New()
+	l.run(source)
 
 	// back to normal state
 	w.Close()
@@ -69,7 +70,8 @@ func TestRunFile(t *testing.T) {
 	if err := tmpfile.Close(); err != nil {
 		t.Fatal(err)
 	}
-	RunFile(tmpfile.Name())
+	l := New()
+	l.RunFile(tmpfile.Name())
 
 	// back to normal state
 	w.Close()
@@ -101,7 +103,8 @@ func TestError(t *testing.T) {
 
 	line := 1
 	message := "Unexpected character."
-	Error(line, message)
+	l := New()
+	l.Error(line, message)
 
 	// back to normal state
 	w.Close()
@@ -134,7 +137,8 @@ func TestReport(t *testing.T) {
 	line := 1
 	where := "at 'foo'"
 	message := "Unexpected character."
-	report(line, where, message)
+	l := New()
+	l.report(line, where, message)
 
 	// back to normal state
 	w.Close()
@@ -166,7 +170,8 @@ func TestRunPrompt(t *testing.T) {
 	wIn.Write([]byte(input))
 	wIn.Close()
 
-	RunPrompt()
+	l := New()
+	l.RunPrompt()
 
 	wOut.Close()
 	os.Stdin = oldStdin

parser/expr.go

@@ -0,0 +1,59 @@
+package parser
+
+import "golox/token"
+
+type ExprVisitor[T any] interface {
+	VisitErrorExpr(error *ErrorExpr) T
+	VisitBinaryExpr(binary *BinaryExpr) T
+	VisitGroupingExpr(grouping *GroupingExpr) T
+	VisitLiteralExpr(literal *LiteralExpr) T
+	VisitUnaryExpr(unary *UnaryExpr) T
+}
+
+type Expr interface {
+	Accept(visitor ExprVisitor[any]) any
+}
+
+type ErrorExpr struct {
+	Value string
+}
+
+func (t *ErrorExpr) Accept(visitor ExprVisitor[any]) any {
+	return visitor.VisitErrorExpr(t)
+}
+
+type BinaryExpr struct {
+	Left Expr
+	Operator token.Token
+	Right Expr
+}
+
+func (t *BinaryExpr) Accept(visitor ExprVisitor[any]) any {
+	return visitor.VisitBinaryExpr(t)
+}
+
+type GroupingExpr struct {
+	Expression Expr
+}
+
+func (t *GroupingExpr) Accept(visitor ExprVisitor[any]) any {
+	return visitor.VisitGroupingExpr(t)
+}
+
+type LiteralExpr struct {
+	Value any
+}
+
+func (t *LiteralExpr) Accept(visitor ExprVisitor[any]) any {
+	return visitor.VisitLiteralExpr(t)
+}
+
+type UnaryExpr struct {
+	Operator token.Token
+	Right Expr
+}
+
+func (t *UnaryExpr) Accept(visitor ExprVisitor[any]) any {
+	return visitor.VisitUnaryExpr(t)
+}
+

parser/parser.go

@@ -0,0 +1,207 @@
+/* Description: This file contains the recursivde descent parser implementation.
+ * The parser is responsible for parsing the tokens generated by the scanner.
+ *
+ * The grammar is as follows:
+ * expression     → equality ;
+ * equality       → comparison ( ( "!=" | "==" ) comparison )* ;
+ * comparison     → term ( ( ">" | ">=" | "<" | "<=" ) term )* ;
+ * term           → factor ( ( "-" | "+" ) factor )* ;
+ * factor         → unary ( ( "/" | "*" ) unary )* ;
+ * unary          → ( "!" | "-" ) unary
+ *               | primary ;
+ * primary        → NUMBER | STRING | "true" | "false" | "nil"
+ *               | "(" expression ")" ;
+ */
+package parser
+
+import (
+	"golox/errors"
+	"golox/token"
+)
+
+// Parser is a recursive descent parser.
+type Parser struct {
+	tokens    []token.Token
+	current   int
+	errLogger errors.Logger
+}
+
+// New creates a new Parser.
+func New(tokens []token.Token, el errors.Logger) *Parser {
+	return &Parser{tokens: tokens, current: 0, errLogger: el}
+}
+
+// Parse parses the tokens and returns the AST.
+func (p *Parser) Parse() Expr {
+	return p.expression()
+}
+
+// expression → equality ;
+func (p *Parser) expression() Expr {
+	return p.equality()
+}
+
+// equality → comparison ( ( "!=" | "==" ) comparison )* ;
+func (p *Parser) equality() Expr {
+	expr := p.comparison()
+
+	for p.match(token.BANG_EQUAL, token.EQUAL_EQUAL) {
+		operator := p.previous()
+		right := p.comparison()
+		expr = &BinaryExpr{Left: expr, Operator: operator, Right: right}
+	}
+
+	return expr
+}
+
+// comparison → term ( ( ">" | ">=" | "<" | "<=" ) term )* ;
+func (p *Parser) comparison() Expr {
+	expr := p.term()
+
+	for p.match(token.GREATER, token.GREATER_EQUAL, token.LESS, token.LESS_EQUAL) {
+		operator := p.previous()
+		right := p.term()
+		expr = &BinaryExpr{Left: expr, Operator: operator, Right: right}
+	}
+
+	return expr
+}
+
+// term → factor ( ( "-" | "+" ) factor )* ;
+func (p *Parser) term() Expr {
+	expr := p.factor()
+
+	for p.match(token.MINUS, token.PLUS) {
+		operator := p.previous()
+		right := p.factor()
+		expr = &BinaryExpr{Left: expr, Operator: operator, Right: right}
+	}
+
+	return expr
+}
+
+// factor → unary ( ( "/" | "*" ) unary )* ;
+func (p *Parser) factor() Expr {
+	expr := p.unary()
+
+	for p.match(token.SLASH, token.STAR) {
+		operator := p.previous()
+		right := p.unary()
+		expr = &BinaryExpr{Left: expr, Operator: operator, Right: right}
+	}
+
+	return expr
+}
+
+// unary → ( "!" | "-" ) unary | primary ;
+func (p *Parser) unary() Expr {
+	if p.match(token.BANG, token.MINUS) {
+		operator := p.previous()
+		right := p.unary()
+		return &UnaryExpr{Operator: operator, Right: right}
+	}
+
+	return p.primary()
+}
+
+// primary → NUMBER | STRING | "true" | "false" | "nil" | "(" expression ")" ;
+func (p *Parser) primary() Expr {
+	switch {
+	case p.match(token.FALSE):
+		return &LiteralExpr{Value: false}
+	case p.match(token.TRUE):
+		return &LiteralExpr{Value: true}
+	case p.match(token.NIL):
+		return &LiteralExpr{Value: nil}
+	case p.match(token.NUMBER, token.STRING):
+		return &LiteralExpr{Value: p.previous().Literal}
+	case p.match(token.LEFT_PAREN):
+		expr := p.expression()
+		err := p.consume(token.RIGHT_PAREN, "Expect ')' after expression.")
+		if err != nil {
+			return err
+		}
+		return &GroupingExpr{Expression: expr}
+	}
+
+	return p.newErrorExpr(p.peek(), "Expect expression.")
+}
+
+// match checks if the current token is any of the given types.
+func (p *Parser) match(types ...token.TokenType) bool {
+	for _, t := range types {
+		if p.check(t) {
+			p.advance()
+			return true
+		}
+	}
+
+	return false
+}
+
+// consume consumes the current token if it is of the given type.
+func (p *Parser) consume(tt token.TokenType, message string) *ErrorExpr {
+	if p.check(tt) {
+		p.advance()
+		return nil
+	}
+
+	return p.newErrorExpr(p.peek(), message)
+}
+
+// check checks if the current token is of the given type.
+func (p *Parser) check(tt token.TokenType) bool {
+	if p.isAtEnd() {
+		return false
+	}
+
+	return p.peek().Type == tt
+}
+
+// advance advances the current token and returns the previous token.
+func (p *Parser) advance() token.Token {
+	if !p.isAtEnd() {
+		p.current++
+	}
+
+	return p.previous()
+}
+
+// isAtEnd checks if the parser has reached the end of the tokens.
+func (p *Parser) isAtEnd() bool {
+	return p.peek().Type == token.EOF
+}
+
+// peek returns the current token.
+func (p *Parser) peek() token.Token {
+	return p.tokens[p.current]
+}
+
+// previous returns the previous token.
+func (p *Parser) previous() token.Token {
+	return p.tokens[p.current-1]
+}
+
+// newErrorExpr creates a new ErrorExpr and reports the error.
+func (p *Parser) newErrorExpr(t token.Token, message string) *ErrorExpr {
+	p.errLogger.ErrorAtToken(t, message)
+	return &ErrorExpr{Value: message}
+}
+
+// synchronize synchronizes the parser after an error.
+func (p *Parser) synchronize() {
+	p.advance()
+
+	for !p.isAtEnd() {
+		if p.previous().Type == token.SEMICOLON {
+			return
+		}
+
+		switch p.peek().Type {
+		case token.CLASS, token.FUN, token.VAR, token.FOR, token.IF, token.WHILE, token.PRINT, token.RETURN:
+			return
+		}
+
+		p.advance()
+	}
+}

scanner/scanner.go

@@ -1,7 +1,7 @@
 package scanner
 
 import (
-	"golox/lox"
+	"golox/errors"
 	"golox/token"
 	"strconv"
 )
@@ -9,21 +9,23 @@ import (
 // Scanner is a struct that holds the source code, the start and current position
 // of the scanner, the current line, and the tokens that have been scanned.
 type Scanner struct {
-	source  string
-	start   int
-	current int
-	line    int
-	tokens  []token.Token
+	source    string
+	start     int
+	current   int
+	line      int
+	tokens    []token.Token
+	errLogger errors.Logger
 }
 
 // New creates a new Scanner struct with the given source code.
-func New(source string) *Scanner {
+func New(source string, el errors.Logger) *Scanner {
 	return &Scanner{
-		source:  source,          // The source code to scan.
-		start:   0,               // The start position of the scanner.
-		current: 0,               // The current position of the scanner.
-		line:    1,               // The current line number.
-		tokens:  []token.Token{}, // The tokens that have been scanned.
+		source:    source,          // The source code to scan.
+		start:     0,               // The start position of the scanner.
+		current:   0,               // The current position of the scanner.
+		line:      1,               // The current line number.
+		tokens:    []token.Token{}, // The tokens that have been scanned.
+		errLogger: el,              // The error logger.
 	}
 }
 
@@ -113,7 +115,7 @@ func (s *Scanner) scanToken() {
 		if isAlpha(c) {
 			s.identifier()
 		} else {
-			lox.Error(s.line, "Unexpected character.")
+			s.errLogger.Error(s.line, "Unexpected character.")
 		}
 	}
 }
@@ -151,7 +153,7 @@ func (s *Scanner) number() {
 	f, err := strconv.ParseFloat(s.source[s.start:s.current], 64)
 
 	if err != nil {
-		lox.Error(s.line, "Could not parse number.")
+		s.errLogger.Error(s.line, "Could not parse number.")
 		return
 	}
 
@@ -168,7 +170,7 @@ func (s *Scanner) string() {
 	}
 
 	if s.isAtEnd() {
-		lox.Error(s.line, "Unterminated string.")
+		s.errLogger.Error(s.line, "Unterminated string.")
 		return
 	}
 

scanner/scanner_test.go

@@ -5,6 +5,18 @@ import (
 	"testing"
 )
 
+type errorLogger struct{}
+
+func (el *errorLogger) Error(line int, message string) {
+}
+
+func (el *errorLogger) ErrorAtToken(t token.Token, message string) {
+}
+
+func newErrorLogger() *errorLogger {
+	return &errorLogger{}
+}
+
 func TestScanTokens(t *testing.T) {
 	tests := []struct {
 		name   string
@@ -76,7 +88,7 @@ func TestScanTokens(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			scanner := New(tt.source)
+			scanner := New(tt.source, newErrorLogger())
 			tokens := scanner.ScanTokens()
 
 			if len(tokens) != len(tt.tokens)+1 { // +1 for EOF token
@@ -108,7 +120,7 @@ func TestIsAtEnd(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			scanner := New(tt.source)
+			scanner := New(tt.source, newErrorLogger())
 			if got := scanner.isAtEnd(); got != tt.expected {
 				t.Errorf("expected %v, got %v", tt.expected, got)
 			}
@@ -129,7 +141,7 @@ func TestMatch(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			scanner := New(tt.source)
+			scanner := New(tt.source, newErrorLogger())
 			if got := scanner.match(tt.char); got != tt.expected {
 				t.Errorf("expected %v, got %v", tt.expected, got)
 			}
@@ -149,7 +161,7 @@ func TestPeek(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			scanner := New(tt.source)
+			scanner := New(tt.source, newErrorLogger())
 			if got := scanner.peek(); got != tt.expected {
 				t.Errorf("expected %v, got %v", tt.expected, got)
 			}
@@ -169,7 +181,7 @@ func TestPeekNext(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			scanner := New(tt.source)
+			scanner := New(tt.source, newErrorLogger())
 			if got := scanner.peekNext(); got != tt.expected {
 				t.Errorf("expected %v, got %v", tt.expected, got)
 			}
@@ -188,7 +200,7 @@ func TestAdvance(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			scanner := New(tt.source)
+			scanner := New(tt.source, newErrorLogger())
 			if got := scanner.advance(); got != tt.expected {
 				t.Errorf("expected %v, got %v", tt.expected, got)
 			}
@@ -246,7 +258,7 @@ func TestString(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			scanner := New(tt.source)
+			scanner := New(tt.source, newErrorLogger())
 			scanner.advance() // Move to the first character of the string
 			scanner.string()
 			if tt.expected == "" {
@@ -276,7 +288,7 @@ func TestNumber(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			scanner := New(tt.source)
+			scanner := New(tt.source, newErrorLogger())
 			scanner.number()
 			if tt.expected == 0 {
 				if len(scanner.tokens) != 0 {
@@ -328,7 +340,7 @@ func TestScanToken(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			scanner := New(tt.source)
+			scanner := New(tt.source, newErrorLogger())
 			scanner.scanToken()
 			if len(scanner.tokens) > 0 {
 				if scanner.tokens[0].Type != tt.expected {
@@ -368,7 +380,7 @@ func TestIdentifier(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			scanner := New(tt.source)
+			scanner := New(tt.source, newErrorLogger())
 			scanner.identifier()
 			if len(scanner.tokens) != 1 {
 				t.Fatalf("expected 1 token, got %d", len(scanner.tokens))