parse statements

parser/parser.go

@@ -1,20 +1,26 @@
 package parser
 
 import (
+	"fmt"
+
 	"gointerpreter/ast"
 	"gointerpreter/lexer"
 	"gointerpreter/token"
 )
 
 type Parser struct {
-	l *lexer.Lexer
+	l      *lexer.Lexer
+	errors []string
 
 	currToken token.Token
 	peekToken token.Token
 }
 
 func New(l *lexer.Lexer) *Parser {
-	p := &Parser{l: l}
+	p := &Parser{
+		l:      l,
+		errors: []string{},
+	}
 
 	p.nextToken()
 	p.nextToken()
@@ -28,5 +34,88 @@ func (p *Parser) nextToken() {
 }
 
 func (p *Parser) ParseProgram() *ast.Program {
-	return nil
+	program := &ast.Program{
+		Statements: []ast.Statement{},
+	}
+
+	for p.currToken.Type != token.EOF {
+		statement := p.parseStatement()
+		if statement != nil {
+			program.Statements = append(program.Statements, statement)
+		}
+
+		p.nextToken()
+	}
+
+	return program
+}
+
+func (p *Parser) parseStatement() ast.Statement {
+	switch p.currToken.Type {
+	case token.LET:
+		return p.parseLetStatement()
+	case token.RETURN:
+		return p.parseReturnStatement()
+	default:
+		return nil
+	}
+}
+
+func (p *Parser) parseReturnStatement() *ast.ReturnStatement {
+	stmt := &ast.ReturnStatement{Token: p.currToken}
+
+	p.nextToken()
+
+	for !p.currTokenIs(token.SEMICOLON) {
+		p.nextToken()
+	}
+
+	return stmt
+}
+
+func (p *Parser) parseLetStatement() *ast.LetStatement {
+	stmt := &ast.LetStatement{Token: p.currToken}
+
+	if !p.expectPeek(token.IDENT) {
+		return nil
+	}
+
+	stmt.Name = &ast.Identifier{Token: p.currToken, Value: p.currToken.Literal}
+
+	if !p.expectPeek(token.ASSIGN) {
+		return nil
+	}
+
+	for !p.currTokenIs(token.SEMICOLON) {
+		p.nextToken()
+	}
+
+	return stmt
+}
+
+func (p *Parser) currTokenIs(t token.TokenType) bool {
+	return p.currToken.Type == t
+}
+
+func (p *Parser) peekTokenIs(t token.TokenType) bool {
+	return p.peekToken.Type == t
+}
+
+func (p *Parser) expectPeek(t token.TokenType) bool {
+	if p.peekTokenIs(t) {
+		p.nextToken()
+		return true
+	}
+
+	p.peekError(t)
+	return false
+}
+
+func (p *Parser) Errors() []string {
+	return p.errors
+}
+
+func (p *Parser) peekError(t token.TokenType) {
+	msg := fmt.Sprintf("expected next token to be [%s], got [%s] instead", t, p.peekToken.Type)
+	p.errors = append(p.errors, msg)
 }