diff options
Diffstat (limited to '')
| -rw-r--r-- | users/fcuny/exp/monkey/pkg/lexer/lexer.go | 28 |
1 files changed, 26 insertions, 2 deletions
diff --git a/users/fcuny/exp/monkey/pkg/lexer/lexer.go b/users/fcuny/exp/monkey/pkg/lexer/lexer.go index d538cf5..06d526e 100644 --- a/users/fcuny/exp/monkey/pkg/lexer/lexer.go +++ b/users/fcuny/exp/monkey/pkg/lexer/lexer.go @@ -56,6 +56,16 @@ func (l *Lexer) skipWhitespace() { } } +// peekChar returns the character at position (which is the next charatecter), +// but does not increment `readPosition` and `position`. +// This is needed to read tokens that are composed of two characters (e.g. `==`). +func (l *Lexer) peekChar() byte { + if l.readPosition >= len(l.input) { + return 0 + } + return l.input[l.readPosition] +} + // NextToken reads the next token from the lexer and returns the current token. func (l *Lexer) NextToken() token.Token { var tok token.Token @@ -64,13 +74,27 @@ func (l *Lexer) NextToken() token.Token { switch l.ch { case '=': - tok = newToken(token.ASSIGN, l.ch) + 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.PLUS, l.ch) case '-': tok = newToken(token.MINUS, l.ch) case '!': - tok = newToken(token.BANG, l.ch) + 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 '/': |