Dear Template Haskell users There was a little exchange about TH quasiquotes a few weeks back (see below). I've made a ticket and some concrete proposals here http://hackage.haskell.org/trac/ghc/ticket/5348 Do take a look, if you care about TH quasiquotes. Simon | -----Original Message----- | From: glasgow-haskell-users-bounces@haskell.org [mailto:glasgow-haskell-users- | bounces@haskell.org] On Behalf Of Simon Marlow | Sent: 11 July 2011 13:43 | To: gale@sefer.org | Cc: GHC users; Ben Millwood | Subject: Re: Quoting a quasi-quote | | On 30/06/2011 14:52, Yitzchak Gale wrote: | > It was pointed out by Ben Millwood on the Cafe | > that there is an undocumented way to escape the | > closing oxford bracket of a quasi-quote using | > a backslash: | > | > [s|This quasi-quote contains this, \|], an escaped | > closing oxford bracket.|] | > | > The backslash itself cannot be escaped in this | > way: | > | > [s|Also contains an escaped bracket \\|] |] | > | > Thus there is a fairly strong limitation on the | > contents of a quasi-quote: it can never end | > in a backslash. | > | > This behavior is not mentioned in the GHC docs. | > Is it a mistake, or is it meant to be a supported | > feature? | > | > This behavior is a bit surprising to me. Since the | > whole point of a quasi-quoter is to allow the user | > to define syntax, you would think that the syntax | > for the quasi-quote itself would be as quiet as | > possible and stay out of the way. People who | > need to be able to escape the closing bracket | > can easily define their own syntax to do so. | > | > In any case, if this is indeed a feature, it certainly | > should be documented. | | It looks intentional to me: | | lex_quasiquote :: String -> P String | lex_quasiquote s = do | i <- getInput | case alexGetChar' i of | Nothing -> lit_error i | | Just ('\\',i) | | Just ('|',i) <- next -> do | setInput i; lex_quasiquote ('|' : s) | | Just (']',i) <- next -> do | setInput i; lex_quasiquote (']' : s) | where next = alexGetChar' i | | Just ('|',i) | | Just (']',i) <- next -> do | setInput i; return s | where next = alexGetChar' i | | Just (c, i) -> do | setInput i; lex_quasiquote (c : s) | | | Indeed, it also seems strange that "\\]" is interpreted as "]". | | That's all I know. I agree we should either document or remove the feature. | | Cheers, | Simon | | | _______________________________________________ | Glasgow-haskell-users mailing list | Glasgow-haskell-users@haskell.org | http://www.haskell.org/mailman/listinfo/glasgow-haskell-users