Improve pretty-printing for HsSyn

[ghc-hetmet.git] / compiler / hsSyn / HsUtils.lhs

diff --git a/compiler/hsSyn/HsUtils.lhs b/compiler/hsSyn/HsUtils.lhs
index 8cef12e..0f75769 100644 (file)
--- a/compiler/hsSyn/HsUtils.lhs
+++ b/compiler/hsSyn/HsUtils.lhs
@@ -13,11 +13,11 @@ which deal with the intantiated versions are located elsewhere:
    Id                  typecheck/TcHsSyn       
 
 \begin{code}
    Id                  typecheck/TcHsSyn       
 
 \begin{code}

-{-# OPTIONS_GHC -w #-}
+{-# OPTIONS -w #-}

 -- The above warning supression flag is a temporary kludge.
 -- While working on this module you are encouraged to remove it and fix
 -- any warnings in the module. See
 -- The above warning supression flag is a temporary kludge.
 -- While working on this module you are encouraged to remove it and fix
 -- any warnings in the module. See

---     http://hackage.haskell.org/trac/ghc/wiki/WorkingConventions#Warnings
+--     http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings

 -- for details
 
 module HsUtils where
 -- for details
 
 module HsUtils where

@@ -32,6 +32,7 @@ import HsLit
 
 import RdrName
 import Var
 
 import RdrName
 import Var

+import Coercion

 import Type
 import DataCon
 import Name
 import Type
 import DataCon
 import Name

@@ -89,6 +90,10 @@ mkHsWrap :: HsWrapper -> HsExpr id -> HsExpr id
 mkHsWrap co_fn e | isIdHsWrapper co_fn = e
                 | otherwise          = HsWrap co_fn e
 
 mkHsWrap co_fn e | isIdHsWrapper co_fn = e
                 | otherwise          = HsWrap co_fn e
 

+mkHsWrapCoI :: CoercionI -> HsExpr id -> HsExpr id
+mkHsWrapCoI IdCo     e = e
+mkHsWrapCoI (ACo co) e = mkHsWrap (WpCo co) e
+

 mkHsLam :: [LPat id] -> LHsExpr id -> LHsExpr id
 mkHsLam pats body = mkHsPar (L (getLoc body) (HsLam matches))
        where
 mkHsLam :: [LPat id] -> LHsExpr id -> LHsExpr id
 mkHsLam pats body = mkHsPar (L (getLoc body) (HsLam matches))
        where

@@ -413,6 +418,22 @@ collectPatBinders.  In a lazy pattern, for example f ~(C x y) = ...,
 we want to generate bindings for x,y but not for dictionaries bound by
 C.  (The type checker ensures they would not be used.)
 
 we want to generate bindings for x,y but not for dictionaries bound by
 C.  (The type checker ensures they would not be used.)
 

+Desugaring of arrow case expressions needs these bindings (see DsArrows
+and arrowcase1), but SPJ (Jan 2007) says it's safer for it to use its
+own pat-binder-collector:
+
+Here's the problem.  Consider
+
+data T a where
+   C :: Num a => a -> Int -> T a
+
+f ~(C (n+1) m) = (n,m)
+
+Here, the pattern (C (n+1)) binds a hidden dictionary (d::Num a),
+and *also* uses that dictionary to match the (n+1) pattern.  Yet, the
+variables bound by the lazy pattern are n,m, *not* the dictionary d.
+So in mkSelectorBinds in DsUtils, we want just m,n as the variables bound.
+

 \begin{code}
 collectSigTysFromPats :: [InPat name] -> [LHsType name]
 collectSigTysFromPats pats = foldr collect_lpat [] pats
 \begin{code}
 collectSigTysFromPats :: [InPat name] -> [LHsType name]
 collectSigTysFromPats pats = foldr collect_lpat [] pats