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module Pretty(Doc,(<>),($$),text,sep,nest,pretty) where infixl <> infixl $$ data Doc = Nil -- text "" | NilAbove Doc -- text "" $$ x | Str `TextBeside` Doc-- text s <> x | Nest Int Doc -- nest k x | Doc `Union` Doc -- x U y | Empty -- {} type Str = (Int,String->String) -- optimised rep of strings: fast length, fast concat. len (i,_) = i (i,s) `cat` (j,t) = (i+j,s.t) str s = (length s,(s++)) string (i,s) = s [] text s = str s `TextBeside` Nil nest k x = Nest k x x $$ y = aboveNest x 0 y aboveNest Nil k y = NilAbove (nest k y) aboveNest (NilAbove x) k y = NilAbove (aboveNest x k y) aboveNest (s `TextBeside` x) k y = seq k' (s `TextBeside` (aboveNest (Nil<>x) k' y)) where k' = k-len s aboveNest (Nest k' x) k y = seq k'' (Nest k' (aboveNest x k'' y)) where k'' = k-k' aboveNest (x `Union` y) k z = aboveNest x k z `Union` aboveNest y k z aboveNest Empty k x = Empty Nil <> (Nest k x) = Nil <> x Nil <> x = x NilAbove x <> y = NilAbove (x <> y) (s `TextBeside` x) <> y = s `TextBeside` (x <> y) Nest k x <> y = Nest k (x <> y) Empty <> y = Empty (x `Union` y) <> z = (x <> z) `Union` (y <> z) sep [x] = x sep (x:ys) = sep' x 0 ys -- sep' x k ys = sep [x,nest k y1,...,nest k yn] sep' Nil k ys = fit (foldl (<+>) Nil ys) `Union` vertical Nil k ys sep' (NilAbove x) k ys = vertical (NilAbove x) k ys sep' (s `TextBeside` x) k ys = s `TextBeside` sep' (Nil <> x) (k-len s) ys sep' (Nest n x) k ys = Nest n (sep' x (k-n) ys) sep' (x `Union` y) k ys = sep' x k ys `Union` vertical y k ys sep' Empty k ys = Empty vertical x k ys = x $$ nest k (foldr1 ($$) ys) x <+> y = x <> text " " <> y fit Nil = Nil fit (NilAbove x) = Empty fit (s `TextBeside` x) = s `TextBeside` (fit x) fit (Nest n x) = Nest n (fit x) fit (x `Union` y) = fit x fit Empty = Empty best w r Nil = Nil best w r (NilAbove x) = NilAbove (best w r x) best w r (s `TextBeside` x) = s `TextBeside` best' w r s x best w r (Nest k x) = Nest k (best (w-k) r x) best w r (x `Union` y) = nicest w r (best w r x) (best w r y) best w r Empty = Empty best' w r s Nil = Nil best' w r s (NilAbove x) = NilAbove (best (w-len s) r x) best' w r s (t `TextBeside` x) = t `TextBeside` best' w r (s `cat` t) x best' w r s (Nest k x) = best' w r s x best' w r s (x `Union` y) = nicest' w r s (best' w r s x) (best' w r s y) best' w r s Empty = Empty nicest w r x y = nicest' w r (str "") x y nicest' w r s x y = if fits (w `min` r) (len s) x then x else y fits n k x = if n True NilAbove y -> True t `TextBeside` y -> fits n (k+len t) y Empty -> False layout k (Nest k' x) = layout (k+k') x layout k x = [' ' | i<-[1..k]] ++ layout' k x layout' k Nil = "\n" layout' k (NilAbove x) = "\n" ++ layout k x layout' k (s `TextBeside` x) = string s ++ layout' (k+len s) x pretty w r d = layout 0 (best w r d) instance Show Doc where show = pretty 80 60