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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) {
msg := fmt.Sprintf("expected next token to be %s, got %s instead",
t, p.peekToken.Type)
p.errors = append(p.errors, msg)
}
func (p *Parser) NextToken() {
p.curToken = p.peekToken
p.peekToken = p.l.NextToken()
}
func (p *Parser) Errors() []string {
return p.errors
}
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{}
for p.curToken.Type != token.EOF {
stmt := p.parseStatement()
if stmt != nil {
program.Statements = append(program.Statements, stmt)
}
p.NextToken()
}
return program
}
func (p *Parser) parseStatement() ast.Statement {
switch p.curToken.Type {
case token.LET:
return p.parseLetStatement()
case token.RETURN:
return p.parseReturnStatement()
default:
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 {
stmt := &ast.LetStatement{Token: p.curToken}
if !p.expectPeek(token.IDENT) {
return nil
}
stmt.Name = &ast.Identifier{Token: p.curToken, Value: p.curToken.Literal}
if !p.expectPeek(token.ASSIGN) {
return nil
}
// TODO: We're skipping the expressions until we encounter a semicolon
for !p.curTokenIs(token.SEMICOLON) {
p.NextToken()
}
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
}
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
} else {
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)
}
|
