identifier expression parser

parser/parser.go

@@ -6,13 +6,32 @@ import (
 	"github.com/54L1m/mil-lang/token"
 )
 
+const (
+	_ int = iota
+	LOWEST
+	EQUALS      // =
+	LESSGREATER // < OR >
+	SUM         // +
+	PRODUCT     // *
+	PREFIX      // -X OR !X
+	CALL        // myFunction(X)
+)
+
+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 New(l *lexer.Lexer) *Parser {
@@ -21,6 +40,9 @@ func New(l *lexer.Lexer) *Parser {
 		errors: []string{},
 	}
 
+	p.prefixParseFns = make(map[token.TokenType]prefixParseFn)
+	p.registerPrefix(token.IDENT, p.parseIdentifier)
+
 	p.nextToken()
 	p.nextToken()
 	return p
@@ -48,11 +70,31 @@ func (p *Parser) parseStatement() ast.Statement {
 	case token.RETURN:
 		return p.parseReturnStatement()
 	default:
-		return nil
+		return p.parseExpressionStatement()
 
 	}
 }
 
+// parsing expressions
+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 {
+		return nil
+	}
+	leftExp := prefix()
+	return leftExp
+}
+
 // parsing var statements
 func (p *Parser) parseVarStatement() *ast.VarStatement {
 	stmt := &ast.VarStatement{Token: p.curToken}

parser/parser_helpers.go

@@ -1,6 +1,9 @@
 package parser
 
-import "github.com/54L1m/mil-lang/token"
+import (
+	"github.com/54L1m/mil-lang/ast"
+	"github.com/54L1m/mil-lang/token"
+)
 
 func (p *Parser) nextToken() {
 	p.curToken = p.peekToken
@@ -24,3 +27,15 @@ func (p *Parser) expectPeek(t token.TokenType) bool {
 		return false
 	}
 }
+
+func (p *Parser) parseIdentifier() ast.Expression {
+	return &ast.Identifier{Token: p.curToken, Value: p.curToken.Literal}
+}
+
+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
+}

parser/parser_test.go

@@ -73,6 +73,34 @@ func TestReturnStatement(t *testing.T) {
 
 }
 
+func TestIdentifierExpression(t *testing.T) {
+	input := "foobar;"
+	l := lexer.New(input)
+	p := New(l)
+	program := p.ParseProgram()
+	checkParseErrors(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 testVarStatement(t *testing.T, s ast.Statement, name string) bool {
 	if s.TokenLiteral() != "var" {
 		t.Errorf("s.TokenLiteral not 'var'. got=%q", s.TokenLiteral())