1 files changed, 110 insertions, 1 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)
+}