Albert Lai <[EMAIL PROTECTED]> wrote:
<snip>
> I wish to toss out a new thought. To that end let me blow up the
> example to underline a scalability issue:
>
> A. q ++ " " ++ a ++ " " ++ z ++ " [" ++ m ++ " -> " ++ k ++ " |" ++ p ++ "| "
> ++ g ++ " -> " ++ c ++ "] " ++ h ++ " " ++ b ++ " " ++ f ++ " " ++ i
> B. printf "%s %s %s [%s -> %s |%s| %s -> %s] %s %s %s %s" q a z m k p g c h
> b f i
>
> B looks clearer because without parsing you can see that the output
> will contain a |blah| between two blah->blah's inside square brackets,
> etc.
>
> A looks clearer because without counting you can see that p is the
> thing that will go into |blah|, the first blah->blah will be m->k,
> etc.
>
> 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? :)
Don't have time to work it out in detail, but something like this sounds
promising:
> lexToken :: String -> alpha -> (String -> String -> alpha) -> alpha
> lexToken (c:s) f x
> | 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 _ f x = 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 s = let
> (s1, s2) = break (=='^') s
> in infixE (Just (litE $ StringL s1))
> (varE '(++))
> (Just (interpolate s2))
Call as $(interpolate "^q ^a ^z [^m -> ^k |^p| ^g -> ^c] ^h ^b ^f ^i").
Note: this is untested code! Be sure and test it before you use it (I
haven't even compiled it).
Confident someone can do better (e.g., formatting parameters, quoting),
Jon Cast
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