-- 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)
| 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