#393: functions without implementations -------------------------------------+------------------------------------- Reporter: c_maeder | Owner: Type: feature request | Status: new Priority: normal | Milestone: ⊥ Component: Compiler (Type | Version: None checker) | Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Iceland_jack): Probably not worth it, but fake definitions are generated for Commentary/PrimOps {{{#!hs newArray# :: Int# -> a -> State# s -> (# State# s,MutableArray# s a #) newArray# = let x = x in x sameMutableArray# :: MutableArray# s a -> MutableArray# s a -> Int# sameMutableArray# = let x = x in x nullAddr# :: Addr# nullAddr# = let x = x in x }}} If this feature is enabled the bodies could be omitted and if we make holes representation-polymorphic (#12531) it's not such a reach to allow top-level unlifted bindings as well when body is omitted: {{{#!hs newArray# :: Int# -> a -> State# s -> (# State# s,MutableArray# s a #) sameMutableArray# :: MutableArray# s a -> MutableArray# s a -> Int# nullAddr# :: NullAddr# }}} This might avoid hacky tests mentioned in `[Compiling GHC.Prim]`. ---- === Note `[Placeholder declarations]` ===

We are generating fake declarations for things in [https://hackage.haskell.org/package/ghc-prim-0.4.0.0/candidate/docs/src /GHC-Prim.html GHC.Prim], just to keep GHC's renamer and typechecker happy enough for what Haddock needs. Our main plan is to say {{{#!hs foo :: <type> foo = foo }}} We have to silence GHC's complaints about unboxed-top-level declarations with an ad-hoc fix in `TcBinds`: see Note `[Compiling GHC.Prim]` in `TcBinds`.

That works for all the primitive functions except `tagToEnum#`. If we generate the binding {{{#!hs tagToEnum# = tagToEnum# }}} GHC will complain about "`tagToEnum#` must appear applied to one argument". We could hack GHC to silence this complaint when compiling `GHC.Prim`, but it seems easier to generate {{{#!hs tagToEnum# = let x = x in x }}} We don't do this for *all* bindings because for ones with an unboxed RHS we would get other complaints (e.g.can't unify "`*`" with "`#`").

Module `GHC.Prim` has no source code: it is the host module for

=== Note `[Compiling GHC.Prim]` === primitive, built-in functions and types. However, for Haddock-ing purposes we generate (via `utils/genprimopcode`) a fake source file `GHC/Prim.hs`, and give it to Haddock, so that it can generate documentation. It contains definitions like

{{{#!hs nullAddr# :: NullAddr# }}} which would normally be rejected as a top-level unlifted binding. But we don't want to complain, because we are only "compiling" this fake mdule [sic] for documentation purposes. Hence this hacky test for `gHC_PRIM` in `checkStrictBinds`.

-- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/393#comment:35 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler