RULES for SPECIALIZ(E)ations

[Simon Peyton-Jones]

| 
| I suppose I'm being bitten by User's Guide 7.8.2:
| 
|   "If more than one rule matches a call, GHC will choose one
arbitrarily
| to apply."
| 
| even if a bit later it says:
| 
|   "So a rule only matches if the types match too."
| 
| Am I understanding right and it's that so?

I think so.  After all, the types match for count/generic too.

Maybe you want a rule

	genericLength = length

which will replace a call to (genericLength at type Int) by a call to
length?


You can also use "phases" to control order of rule application (albeit
it's crude).

	
http://www.haskell.org/ghc/docs/latest/html/users_guide/pragmas.html#PHA
SE-CONTROL

Simon