Monadify specialise/SpecConstr: use do, return and standard monad functions

[ghc-hetmet.git] / compiler / specialise / Specialise.lhs

diff --git a/compiler/specialise/Specialise.lhs b/compiler/specialise/Specialise.lhs
index b3bd6a2..9750bd0 100644 (file)
--- a/compiler/specialise/Specialise.lhs
+++ b/compiler/specialise/Specialise.lhs
@@ -8,7 +8,7 @@
 -- 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/CodingStyle#Warnings
+--     http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
 -- for details
 
 module Specialise ( specProgram ) where
@@ -892,7 +892,8 @@ specDefn subst calls (fn, rhs)
                -- The rule to put in the function's specialisation is:
                --      forall b,d, d1',d2'.  f t1 b t3 d d1' d2' = f1 b d  
            spec_env_rule = mkLocalRule (mkFastString ("SPEC " ++ showSDoc (ppr fn)))
-                               AlwaysActive (idName fn)
+                               inline_prag     -- Note [Auto-specialisation and RULES]
+                               (idName fn)
                                (poly_tyvars ++ rhs_dicts')
                                inst_args 
                                (mkVarApps (Var spec_f) app_args)
@@ -918,6 +919,33 @@ specDefn subst calls (fn, rhs)
         | otherwise               = zipEqual doc xs ys
 \end{code}
 
+Note [Auto-specialisation and RULES]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Consider:
+   g :: Num a => a -> a
+   g = ...
+
+   f :: (Int -> Int) -> Int
+   f w = ...
+   {-# RULE f g = 0 #-}
+
+Suppose that auto-specialisation makes a specialised version of
+g::Int->Int That version won't appear in the LHS of the RULE for f.
+So if the specialisation rule fires too early, the rule for f may
+never fire. 
+
+It might be possible to add new rules, to "complete" the rewrite system.
+Thus when adding
+       RULE forall d. g Int d = g_spec
+also add
+       RULE f g_spec = 0
+
+But that's a bit complicated.  For now we ask the programmer's help,
+by *copying the INLINE activation pragma* to the auto-specialised rule.
+So if g says {-# NOINLINE[2] g #-}, then the auto-spec rule will also
+not be active until phase 2.  
+
+
 Note [Specialisation shape]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
 We only specialise a function if it has visible top-level lambdas