tijani
44d9b2c7ec
git-svn-id: https://svn.tlawal.org/svn/monkey@1 f6afcba9-9ef1-4bdd-9b72-7484f5705bac
103 lines
2.4 KiB
Go
103 lines
2.4 KiB
Go
package lexer
|
|
|
|
import "monkey/token"
|
|
|
|
type Lexer struct {
|
|
input string
|
|
position int // current position in input (the current_char)
|
|
read_position int // current reading position in input (after current_char)
|
|
current_char byte
|
|
}
|
|
|
|
func new(input string) *Lexer {
|
|
l := &Lexer{input: input}
|
|
l.read_char()
|
|
return l
|
|
}
|
|
|
|
func new_token(TokenType token.TokenType, ch byte) token.Token {
|
|
return token.Token{Type: TokenType, Literal: string(ch)}
|
|
}
|
|
|
|
func (lexer *Lexer) read_char() {
|
|
if lexer.read_position >= len(lexer.input) {
|
|
lexer.current_char = 0
|
|
} else {
|
|
lexer.current_char = lexer.input[lexer.read_position]
|
|
}
|
|
lexer.position = lexer.read_position
|
|
lexer.read_position += 1
|
|
}
|
|
|
|
func (lexer *Lexer) read_identifier() string {
|
|
position := lexer.position
|
|
for is_letter(lexer.current_char) {
|
|
lexer.read_char()
|
|
}
|
|
return lexer.input[position:lexer.position]
|
|
}
|
|
|
|
func is_letter(ch byte) bool {
|
|
return 'a' <= ch && ch <= 'z' || 'A' <= ch && ch <= 'Z' || ch == '_'
|
|
}
|
|
|
|
func (lexer *Lexer) skip_whitespace() {
|
|
for lexer.current_char == ' ' || lexer.current_char == '\t' || lexer.current_char == '\n' || lexer.current_char == '\r' {
|
|
lexer.read_char()
|
|
}
|
|
}
|
|
|
|
func (lexer *Lexer) read_number() string {
|
|
position := lexer.position
|
|
for is_digit(lexer.current_char){
|
|
lexer.read_char()
|
|
}
|
|
return lexer.input[position: lexer.position]
|
|
}
|
|
|
|
func is_digit(ch byte) bool{
|
|
return '0' <= ch && ch <= '9'
|
|
}
|
|
|
|
func (lexer *Lexer) next_token() token.Token {
|
|
var tok token.Token
|
|
lexer.skip_whitespace()
|
|
|
|
switch lexer.current_char {
|
|
case '=':
|
|
tok = new_token(token.ASSIGN, lexer.current_char)
|
|
case ';':
|
|
tok = new_token(token.SEMICOLON, lexer.current_char)
|
|
case '(':
|
|
tok = new_token(token.LPAREN, lexer.current_char)
|
|
case ')':
|
|
tok = new_token(token.RPAREN, lexer.current_char)
|
|
case '{':
|
|
tok = new_token(token.LBRACE, lexer.current_char)
|
|
case '}':
|
|
tok = new_token(token.RBRACE, lexer.current_char)
|
|
case ',':
|
|
tok = new_token(token.COMMA, lexer.current_char)
|
|
case '+':
|
|
tok = new_token(token.PLUS, lexer.current_char)
|
|
case 0:
|
|
tok.Literal = ""
|
|
tok.Type = token.EOF
|
|
|
|
default:
|
|
if is_letter(lexer.current_char) {
|
|
tok.Literal = lexer.read_identifier()
|
|
tok.Type = token.LookupIdentifier(tok.Literal)
|
|
return tok
|
|
} else if is_digit(lexer.current_char) {
|
|
tok.Type = token.INT
|
|
tok.Literal = lexer.read_number()
|
|
return tok
|
|
} else {
|
|
tok = new_token(token.ILLEGAL, lexer.current_char)
|
|
}
|
|
}
|
|
lexer.read_char()
|
|
return tok
|
|
}
|