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package lexer
import "github.com/mewsen/interpreter/token"
type Lexer struct {
input string
position int // current position in input (points to current char)
readPosition int // current reading position (after current char)
ch byte // current char
}
func New(input string) *Lexer {
l := Lexer{input: input}
l.readChar()
return &l
}
func (l *Lexer) NextToken() token.Token {
var tok token.Token
l.skipWhitespace()
switch l.ch {
case '=':
if l.peekChar() == '=' {
ch := l.ch
l.readChar()
literal := string(ch) + string(l.ch)
tok = token.Token{Type: token.EQ, Literal: literal}
} else {
tok = newToken(token.ASSIGN, l.ch)
}
case ';':
tok = newToken(token.SEMICOLON, l.ch)
case '(':
tok = newToken(token.LPAREN, l.ch)
case ')':
tok = newToken(token.RPAREN, l.ch)
case '{':
tok = newToken(token.LBRACE, l.ch)
case '}':
tok = newToken(token.RBRACE, l.ch)
case ',':
tok = newToken(token.COMMA, l.ch)
case '+':
tok = newToken(token.PLUS, l.ch)
case '-':
tok = newToken(token.MINUS, l.ch)
case '!':
if l.peekChar() == '=' {
ch := l.ch
l.readChar()
literal := string(ch) + string(l.ch)
tok = token.Token{Type: token.NOT_EQ, Literal: literal}
} else {
tok = newToken(token.BANG, l.ch)
}
case '*':
tok = newToken(token.ASTERISK, l.ch)
case '/':
tok = newToken(token.SLASH, l.ch)
case '<':
tok = newToken(token.LT, l.ch)
case '>':
tok = newToken(token.GT, l.ch)
case 0:
tok.Literal = ""
tok.Type = token.EOF
default:
if isLetter(l.ch) {
tok.Literal = l.readIdentifier()
tok.Type = token.LookupIdentifier(tok.Literal)
return tok
} else if isDigit(l.ch) {
tok.Type = token.INT
tok.Literal = l.readNumber()
return tok
} else {
tok = newToken(token.ILLEGAL, l.ch)
}
}
l.readChar()
return tok
}
func (l *Lexer) readNumber() string {
position := l.position
for isDigit(l.ch) {
l.readChar()
}
return l.input[position:l.position]
}
func isDigit(ch byte) bool {
return '0' <= ch && ch <= '9'
}
func (l *Lexer) peekChar() byte {
if l.readPosition >= len(l.input) {
return 0
} else {
return l.input[l.readPosition]
}
}
func (l *Lexer) skipWhitespace() {
for l.ch == ' ' || l.ch == '\t' || l.ch == '\n' || l.ch == '\r' {
l.readChar()
}
}
func (l *Lexer) readIdentifier() string {
position := l.position
for isLetter(l.ch) {
l.readChar()
}
return l.input[position:l.position]
}
func isLetter(ch byte) bool {
return 'a' <= ch && ch <= 'z' || 'A' <= ch && ch <= 'Z' || ch == '_'
}
func (l *Lexer) readChar() {
if l.readPosition >= len(l.input) {
l.ch = 0
} else {
l.ch = l.input[l.readPosition]
}
l.position = l.readPosition
l.readPosition++
}
func newToken(tokenType token.TokenType, ch byte) token.Token {
return token.Token{Type: tokenType, Literal: string(ch)}
}
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