feat(parser): expressions, literalsHEADmain

Signed-off-by: Michael Tews <michael@tews.dev>

2 files changed, 280 insertions, 2 deletions

diff --git a/parser/parser.go b/parser/parser.go
index 936d58a..a9c381a 100644
--- a/parser/parser.go
+++ b/parser/parser.go
@@ -2,18 +2,46 @@ package parser
 
 import (
 	"fmt"
+	"strconv"
 
 	"github.com/mewsen/interpreter/ast"
 	"github.com/mewsen/interpreter/lexer"
 	"github.com/mewsen/interpreter/token"
 )
 
+const (
+	_ int = iota
+	LOWEST
+	EQUALS
+	LESSGREATER
+	SUM
+	PRODUCT
+	PREFIX
+	CALL
+)
+
+type (
+	prefixParseFn func() ast.Expression
+	infixParseFn  func(ast.Expression) ast.Expression
+)
+
 type Parser struct {
 	l      *lexer.Lexer
 	errors []string
 
 	curToken  token.Token
 	peekToken token.Token
+
+	prefixParseFns map[token.TokenType]prefixParseFn
+	infixParseFns  map[token.TokenType]infixParseFn
+}
+
+func (p *Parser) registerPrefix(tokenType token.TokenType, fn prefixParseFn) {
+	p.prefixParseFns[tokenType] = fn
+}
+
+func (p *Parser) registerInfix(tokenType token.TokenType, fn infixParseFn) {
+	p.infixParseFns[tokenType] = fn
 }
 
 func (p *Parser) peekError(t token.TokenType) {
@@ -34,12 +62,35 @@ func (p *Parser) Errors() []string {
 func New(l *lexer.Lexer) *Parser {
 	p := &Parser{l: l, errors: []string{}}
 
+	p.prefixParseFns = make(map[token.TokenType]prefixParseFn)
+	p.registerPrefix(token.IDENT, p.parseIdentifier)
+	p.registerPrefix(token.INT, p.parseIntegerLiteral)
+	p.registerPrefix(token.BANG, p.parsePrefixExpression)
+	p.registerPrefix(token.MINUS, p.parsePrefixExpression)
+
 	p.NextToken()
 	p.NextToken()
 
 	return p
 }
 
+func (p *Parser) parsePrefixExpression() ast.Expression {
+	expression := &ast.PrefixExpression{
+		Token:    p.curToken,
+		Operator: p.curToken.Literal,
+	}
+
+	p.NextToken()
+
+	expression.Right = p.parseExpression(PREFIX)
+
+	return expression
+}
+
+func (p *Parser) parseIdentifier() ast.Expression {
+	return &ast.Identifier{Token: p.curToken, Value: p.curToken.Literal}
+}
+
 func (p *Parser) ParseProgram() *ast.Program {
 	program := &ast.Program{}
 	program.Statements = []ast.Statement{}
@@ -59,9 +110,25 @@ func (p *Parser) parseStatement() ast.Statement {
 	switch p.curToken.Type {
 	case token.LET:
 		return p.parseLetStatement()
+	case token.RETURN:
+		return p.parseReturnStatement()
 	default:
-		return nil
+		return p.parseExpressionStatement()
+	}
+}
+
+func (p *Parser) parseReturnStatement() *ast.ReturnStatement {
+	stmt := &ast.ReturnStatement{Token: p.curToken}
+
+	p.NextToken()
+
+	// TODO: We're skipping the expressions until
+	// we encounter a semicolon
+	for !p.curTokenIs(token.SEMICOLON) {
+		p.NextToken()
 	}
+
+	return stmt
 }
 
 func (p *Parser) parseLetStatement() *ast.LetStatement {
@@ -85,6 +152,43 @@ func (p *Parser) parseLetStatement() *ast.LetStatement {
 	return stmt
 }
 
+func (p *Parser) parseExpressionStatement() *ast.ExpressionStatement {
+	stmt := &ast.ExpressionStatement{Token: p.curToken}
+
+	stmt.Expression = p.parseExpression(LOWEST)
+
+	if p.peekTokenIs(token.SEMICOLON) {
+		p.NextToken()
+	}
+
+	return stmt
+}
+
+func (p *Parser) parseExpression(precedence int) ast.Expression {
+	prefix := p.prefixParseFns[p.curToken.Type]
+	if prefix == nil {
+		p.noPrefixParseFnError(p.curToken.Type)
+		return nil
+	}
+	leftExp := prefix()
+	return leftExp
+}
+
+func (p *Parser) parseIntegerLiteral() ast.Expression {
+	lit := &ast.IntegerLiteral{Token: p.curToken}
+
+	value, err := strconv.ParseInt(p.curToken.Literal, 0, 64)
+	if err != nil {
+		msg := fmt.Sprintf("could not parse %q as integer", p.curToken.Literal)
+		p.errors = append(p.errors, msg)
+		return nil
+	}
+
+	lit.Value = value
+
+	return lit
+}
+
 func (p *Parser) curTokenIs(t token.TokenType) bool {
 	return p.curToken.Type == t
 }
@@ -101,3 +205,8 @@ func (p *Parser) expectPeek(t token.TokenType) bool {
 		return false
 	}
 }
+
+func (p *Parser) noPrefixParseFnError(t token.TokenType) {
+	msg := fmt.Sprintf("no prefix parse function for %s found", t)
+	p.errors = append(p.errors, msg)
+}
diff --git a/parser/parser_test.go b/parser/parser_test.go
index f7158bf..be49bf5 100644
--- a/parser/parser_test.go
+++ b/parser/parser_test.go
@@ -1,9 +1,11 @@
 package parser
 
 import (
+	"fmt"
+	"testing"
+
 	"github.com/mewsen/interpreter/ast"
 	"github.com/mewsen/interpreter/lexer"
-	"testing"
 )
 
 func TestLetStatements(t *testing.T) {
@@ -64,3 +66,170 @@ func testLetStatement(t *testing.T, s ast.Statement, name string) bool {
 
 	return true
 }
+
+func TestReturnStatement(t *testing.T) {
+	input := `
+return 5;
+return 10;
+return 993322;
+	`
+
+	l := lexer.New(input)
+	p := New(l)
+
+	program := p.ParseProgram()
+
+	checkParserErrors(t, p)
+
+	if len(program.Statements) != 3 {
+		t.Fatalf("program.Statements does not contain 3 statement. got=%d", len(program.Statements))
+	}
+
+	for _, stmt := range program.Statements {
+		returnStmt, ok := stmt.(*ast.ReturnStatement)
+		if !ok {
+			t.Errorf("stmt not *ast.returnStatement, got=%T", stmt)
+			continue
+		}
+		if returnStmt.TokenLiteral() != "return" {
+			t.Errorf("returnStmt.TokenLiteral not 'return', got=%q", returnStmt.TokenLiteral())
+		}
+	}
+}
+
+func TestIdentifierExpression(t *testing.T) {
+	input := "foobar;"
+
+	l := lexer.New(input)
+	p := New(l)
+	program := p.ParseProgram()
+
+	checkParserErrors(t, p)
+
+	if len(program.Statements) != 1 {
+		t.Fatalf("program has not enough statements. got=%d",
+			len(program.Statements))
+	}
+
+	stmt, ok := program.Statements[0].(*ast.ExpressionStatement)
+	if !ok {
+		t.Fatalf("program.Statements[0] is not ast.ExpressionStatement. got=%T",
+			program.Statements[0])
+	}
+
+	ident, ok := stmt.Expression.(*ast.Identifier)
+	if !ok {
+		t.Fatalf("exp not *ast.Identifier. got=%T", stmt.Expression)
+	}
+
+	if ident.Value != "foobar" {
+		t.Errorf("ident.Value not %s. got=%s", "foobar", ident.Value)
+	}
+
+	if ident.TokenLiteral() != "foobar" {
+		t.Errorf("ident.TokenLiteral not %s. got=%s", "foobar",
+			ident.TokenLiteral())
+	}
+}
+
+func checkParserErrors(t *testing.T, p *Parser) {
+	for _, err := range p.errors {
+		t.Fatal(err)
+	}
+}
+
+func TestIntegerLiteralExpression(t *testing.T) {
+	input := "5;"
+
+	l := lexer.New(input)
+	p := New(l)
+	program := p.ParseProgram()
+	checkParserErrors(t, p)
+
+	if len(program.Statements) != 1 {
+		t.Fatalf("program has not enough statements. got=%d",
+			len(program.Statements))
+	}
+	stmt, ok := program.Statements[0].(*ast.ExpressionStatement)
+	if !ok {
+		t.Fatalf("exp not *ast.IntergerLiteral. got=%T", program.Statements[0])
+	}
+
+	literal, ok := stmt.Expression.(*ast.IntegerLiteral)
+	if !ok {
+		t.Fatalf("literal.Value not %d, got=%d", 5, stmt.Expression)
+	}
+
+	if literal.Value != 5 {
+		t.Errorf("literal.Value not %d. got=%d", 5, literal.Value)
+	}
+
+	if literal.TokenLiteral() != "5" {
+		t.Errorf("literal.TokenLiteral not %s. got=%s", "5",
+			literal.TokenLiteral())
+	}
+}
+
+func TestParsingPrefixExpressions(t *testing.T) {
+	prefixTests := []struct {
+		input        string
+		operator     string
+		integerValue int64
+	}{
+		{"!5", "!", 5},
+		{"-15", "-", 15},
+	}
+
+	for _, tt := range prefixTests {
+		l := lexer.New(tt.input)
+		p := New(l)
+		program := p.ParseProgram()
+		checkParserErrors(t, p)
+
+		if len(program.Statements) != 1 {
+			t.Fatalf("program.Statements does not contain %d statements. got=%d\n",
+				1, len(program.Statements))
+		}
+
+		stmt, ok := program.Statements[0].(*ast.ExpressionStatement)
+		if !ok {
+			t.Fatalf("program.Statements[0] is not ast.ExpressionStatement. got=%T",
+				program.Statements[0])
+		}
+
+		exp, ok := stmt.Expression.(*ast.PrefixExpression)
+		if !ok {
+			t.Fatalf("stmt is not ast.PrefixExpression. got=%T", stmt.Expression)
+		}
+
+		if exp.Operator != tt.operator {
+			t.Fatalf("exp.Operator is not %s. got=%s",
+				tt.operator, exp.Operator)
+		}
+
+		if !testIntegerLiteral(t, exp.Right, tt.integerValue) {
+			return
+		}
+	}
+}
+
+func testIntegerLiteral(t *testing.T, il ast.Expression, value int64) bool {
+	integ, ok := il.(*ast.IntegerLiteral)
+	if !ok {
+		t.Errorf("il not *ast.IntegerLiteral. got=%T", il)
+		return false
+	}
+
+	if integ.Value != value {
+		t.Errorf("integ.Value not %d. got=%d", value, integ.Value)
+		return false
+	}
+
+	if integ.TokenLiteral() != fmt.Sprintf("%d", value) {
+		t.Errorf("integ.TokenLiteral not %d. got=%s", value,
+			integ.TokenLiteral())
+		return false
+	}
+
+	return true
+}