PUBLIC Hi,
I'm trying to compile the following two modules:
```
{-# LANGUAGE NoImplicitPrelude #-}
module MiniMonad where
class Functor f where
fmap :: (a -> b) -> f a -> f b
class (Functor f) => Applicative f where
pure :: a -> f a
class (Applicative m) => Monad m where
return :: a -> m a
return = pure
(>>=) :: m a -> (a -> m b) -> m b
infixl 1 >>=
```
```
{-# LANGUAGE NoImplicitPrelude #-}
module SpecMain where
import MiniMonad
data Identity a = MkIdentity a
instance Functor Identity where
fmap f (MkIdentity x) = MkIdentity (f x)
instance Applicative Identity where
pure x = MkIdentity x
instance Monad Identity where
run :: Identity a -> a
run (MkIdentity x) = x
foo :: ()
foo = run (return ())
```
If I compile these from the CLI, I see three rules firing:
```
./_build/stage1/bin/ghc -debug -fforce-recomp -dno-typeable-binds
input/SpecMain.hs -iinput -O0 -ddump-rule-rewrites -dsuppress-all
```
```
[1 of 2] Compiling MiniMonad ( input/MiniMonad.hs, input/MiniMonad.o )
[2 of 2] Compiling SpecMain ( input/SpecMain.hs, input/SpecMain.o )
tc_iface_decl/2 Monad
input/SpecMain.hs:14:10: warning: [-Wmissing-methods]
* No explicit implementation for
'>>='
* In the instance declaration for 'Monad Identity'
|
14 | instance Monad Identity where
| ^^^^^^^^^^^^^^
Rule fired
Rule: Class op $p1Monad
Module: (BUILTIN)
Before: MiniMonad.$p1Monad
TyArg SpecMain.Identity ValArg SpecMain.$fMonadIdentity
After: SpecMain.$fApplicativeIdentity
Cont: StrictArg MiniMonad.pure
ApplyToTy a_avS
Stop[RhsCtxt(Recursive)] a_avS -> SpecMain.Identity a_avS
Rule fired
Rule: Class op pure
Module: (BUILTIN)
Before: MiniMonad.pure
TyArg SpecMain.Identity ValArg SpecMain.$fApplicativeIdentity
After: $cpure_aw8
Cont: ApplyToTy a_avS
Stop[RhsCtxt(Recursive)] a_avS -> SpecMain.Identity a_avS
Rule fired
Rule: Class op return
Module: (BUILTIN)
Before: MiniMonad.return
TyArg SpecMain.Identity ValArg SpecMain.$fMonadIdentity
After: $creturn_avP
Cont: ApplyToTy ()
ApplyToVal nodup hole () -> SpecMain.Identity () GHC.Tuple.Prim.()
Select nodup wild_X1
Stop[RhsCtxt(NonRecursive)] ()
```
However, if I try this via the API (see attached `main.hs`), then only `Class
op return` fires:
```
Processing module MiniMonad
Processing module SpecMain
input/SpecMain.hs:14:10: warning: [-Wmissing-methods]
* No explicit implementation for
'>>='
* In the instance declaration for 'Monad Identity'
|
14 | instance Monad Identity where
| ^^^^^^^^^^^^^^
Rule fired
Rule: Class op return
Module: (BUILTIN)
Before: MiniMonad.return
TyArg SpecMain.Identity ValArg SpecMain.$fMonadIdentity
After: $creturn_aqm
Cont: ApplyToTy ()
ApplyToVal nodup hole () -> SpecMain.Identity () GHC.Tuple.Prim.()
Select nodup wild_X1
Stop[RhsCtxt(NonRecursive)] ()
All done.
```
This of course leads to much worse code further downstream (and is catastrophic
for my use case where I rely on extensive specialisation).
Why is that? What is missing from my `main.hs` that only one of the three
method rules is correctly used when compiling the second module?
Thanks,
Gergo
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main.hs
Description: main.hs
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