87 lines
1.9 KiB
Go
87 lines
1.9 KiB
Go
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package parser
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import (
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"monkey/ast"
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"monkey/lexer"
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"monkey/token"
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)
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type Parser struct {
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lexer *lexer.Lexer
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current_token token.Token
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peek_token token.Token
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}
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func New(l_lexer *lexer.Lexer) *Parser {
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l_parser := &Parser{lexer: l_lexer}
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// Read two tokens so current_token and peek_token are both set
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l_parser.next_token()
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l_parser.next_token()
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return l_parser
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}
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func (l_parser *Parser) ParseProgram() *ast.Program {
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program := &ast.Program{}
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program.Statements = []ast.Statement{}
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for l_parser.current_token.Type != token.EOF {
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statement := l_parser.parse_statement()
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if statement != nil {
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program.Statements = append(program.Statements, statement)
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}
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l_parser.next_token()
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}
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return program
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}
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func (l_parser *Parser) next_token() {
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l_parser.current_token = l_parser.peek_token
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l_parser.peek_token = l_parser.lexer.NextToken()
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}
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func (l_parser *Parser) parse_statement() ast.Statement {
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switch l_parser.current_token.Type {
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case token.LET:
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return l_parser.parse_let_statement()
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default:
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return nil
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}
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}
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func (l_parser *Parser) parse_let_statement() *ast.LetStatement {
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statement := &ast.LetStatement{Token: l_parser.current_token}
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if !l_parser.expect_peek(token.IDENT) {
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return nil
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}
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statement.Name = &ast.Identifier{Token: l_parser.current_token, Value: l_parser.current_token.Literal}
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if !l_parser.expect_peek(token.ASSIGN) {
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return nil
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}
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// TODO(tijani): Skipping the expressins until there is a semicolon
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for !l_parser.current_token_is(token.SEMICOLON) {
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l_parser.next_token()
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}
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return statement
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}
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func (l_parser *Parser) current_token_is(l_token token.TokenType) bool {
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return l_parser.current_token.Type == l_token
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}
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func (l_parser *Parser) peek_token_is(l_token token.TokenType) bool {
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return l_parser.peek_token.Type == l_token
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}
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func (l_parser *Parser) expect_peek(l_token token.TokenType) bool {
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if l_parser.peek_token_is(l_token) {
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l_parser.next_token()
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return true
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} else {
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return false
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}
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}
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