Everyone suggesting that separating lexing and parsing is a "good practice" -- I have to disagree - in many cases performing lexing and parsing in a single pass gives much more power, and performance implications are not as bad as they're presented in the other answers (see Packrat).

This approach shines when one has to mix a number of different languages in a single input stream. This is not only needed by the weird metaprogramming-oriented languages like Katahdin and alike, but for much more mainstream applications as well, like literate programming (mixing latex and, say, C++), using HTML in comments, stuffing Javascript into HTML, and so on.

Everyone suggesting that separating lexing and parsing is a "good practice" -- I have to disagree - in many cases performing lexing and parsing in a single pass gives much more power, and performance implications are not as bad as they're presented in the other answers (see Packrat).

This approach shines when one has to mix a number of different languages in a single input stream. This is not only needed by the weird metaprogramming-oriented languages like Katahdin and alike, but for much more mainstream applications as well, like literate programming (mixing latex and, say, C++), using HTML in comments, stuffing Javascript into HTML, and so on.

Everyone suggesting that separating lexing and parsing is a "good practice". I have to disagree - in many cases performing lexing and parsing in a single pass gives much more power, and performance implications are not that bad as they're presented in the other answers (see Packrat).

This approach shines when one have to mix a number of different languages in a single input stream. This is not only needed by the weird metaprogramming-oriented languages like Katahdin and alike, but for much more mainstream applications as well, like literate programming (mixing latex and, say, C++), using HTML in comments, stuffing Javascript into HTML, and so on.

Everyone suggesting that separating lexing and parsing is a "good practice" -- I have to disagree - in many cases performing lexing and parsing in a single pass gives much more power, and performance implications are not as bad as they're presented in the other answers (see Packrat).

This approach shines when one has to mix a number of different languages in a single input stream. This is not only needed by the weird metaprogramming-oriented languages like Katahdin and alike, but for much more mainstream applications as well, like literate programming (mixing latex and, say, C++), using HTML in comments, stuffing Javascript into HTML, and so on.