Comments on: Adventures in parsing, part 3

By: Magnus

Magnus — Sun, 03 Jun 2007 22:17:47 +0000

Conal and Twan, thanks for your suggestions. I'll put them into practice and post the "final" result as soon as I find some time.

By: Magnus

Magnus — Sun, 03 Jun 2007 22:10:27 +0000

Hmm, this increasing traffic and commenting are highlighting some shortcomings of my wordpress setup it seems

First, Conal, the boxes are due to the theme I’m using, apparently list items are boxed. I don’t like it either and I’ll try to get around modifying the theme.

Twan, I’ve now added a preview plugin for wordpress. It seems to work quite well and hopefully it’ll make it easier to avoid some of editing problems I’ve seen in comments lately.

By: Twan van Laarhoven

Twan van Laarhoven — Sun, 03 Jun 2007 14:49:06 +0000

Damn markdown/lack of preview button. The code block in the previous post should be

parseHex = hexStr2Int <$> many1 hexDigit
parseAddress = Address <$> parseHex <* char '-' <*> parseHex
parseDevice  = Device  <$> parseHex <* char ':' <*> parseHex

By: Twan van Laarhoven

Twan van Laarhoven — Sun, 03 Jun 2007 14:47:24 +0000

First of all, note that you don't need parentheses around parseSomething <* char ' '.

You can also simplify things a bit more by combining hexStr2Int <$> many1 hexDigit into a function, then you could say: parseHex = hexStr2Int many1 hexDigit parseAddress = Address parseHex <* char '-' <> parseHex parseDevice = Device parseHex < char ':' <*> parseHex

Also, in cA, should there be a case for character other than 'p' or 's'? Otherwise the program could fail with a pattern match error.

By: Conal Elliott

Conal Elliott — Sun, 03 Jun 2007 05:40:47 +0000

hm. i wonder why the boxes around list items in my previous reply.

By: Conal Elliott

Conal Elliott — Sun, 03 Jun 2007 05:37:55 +0000

A thing of beauty! I'm glad you stuck with it, Magnus.

Some much smaller points:

The pattern (== c) <$> anyChar (nicely written, btw) arises three times, so it might merit a name.
Similarly for hexStr2Int <$> many1 hexDigit, especially when you rewrite f <$> (a <* b) to (f <$> a) <* b.
The pattern (a <* char ' ') <*> b comes up a lot. How about naming it also, with a nice infix op, say a <#> b?
The cA definition could use pattern matching instead (e.g., cA 'p' = Private and cA 's' = Shared).
Some of your parens are unnecessary (3rd line of parseDevice and last of parseRegion), since application binds more tightly than infix ops.