Albert Lai
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