Jonathan Cast <[EMAIL PROTECTED]> wrote:
> Albert Lai <[EMAIL PROTECTED]> wrote:
> <snip>
> > The best of both worlds may be something like the notation in the HOL
> > theorem prover:
> >
> > ``^q ^a ^z [^m -> ^k |^p| ^g -> ^c] ^h ^b ^f ^i``
> >
> > Do you agree that this is much better?
> >
> > Could someone implement something like this in GHC please? :)
The attached code has been tested and works; call as $(interpolate "^q
^a ^z [^m -> ^k |^p| ^g -> ^c] ^h ^b ^f ^i").
Still confident someone can do better (e.g., formatting parameters),
Jon Cast
module Language.Haskell.Interpolate where
import Char
import Control.Monad.Fix
import Language.Haskell.TH
lexToken :: String -> alpha -> (String -> String -> alpha) -> alpha
lexToken (c:s) x f
| isAlpha c || c == '_'
= flip fix ([c], s) $ \ loop (s1, s2) -> case s2 of
(c:s2') | isAlphaNum c || c == '_' || c == '\''
-> loop (c:s1, s2')
_ -> f (reverse s1) s2
lexToken _ x f = x
interpolate :: String -> Q Exp
interpolate [] = listE []
interpolate ('^':s)
= lexToken s (fail "Expected valid Haskell identifier") $ \ s1 s2 ->
infixE (Just (varE 'show `appE` varE (mkName s1)))
(varE '(++))
(Just (interpolate s2))
interpolate ('\\':c:s) = infixE (Just (litE $ StringL [c]))
(varE '(++))
(Just (interpolate s))
interpolate s = let
(s1, s2) = break (\c -> c =='^' || c == '\\') s
in infixE (Just (litE $ StringL s1))
(varE '(++))
(Just (interpolate s2))
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