For anyone interested, here's a complete list of all foreign imports at the
STG level from base and integer-simple:
https://gist.github.com/chrisdone/24b476862b678a3665fbf9b833a9905f
They all have type (# State# RealWorld #) or (# State# RealWorld,
<something> #).
On Tue, 5 Nov 2019 at 15:18, Christopher Done
Aha, thanks Csaba. So I’m not losing my marbles. The AST has a type signature of the “initial” but implements the “lowered”. So with -ddump-stg we can observe it:
The version claimed in the type signature (returning a tuple):
Foreign.it :: Foreign.C.Types.CDouble [GblId] = [] \u [] case ds_r1HA of { GHC.Types.D# ds2_s1HW [Occ=Once] -> case __pkg_ccall_GC main [ds2_s1HW GHC.Prim.realWorld#] of { (#,#) _ [Occ=Dead] ds4_s1I0 [Occ=Once] -> GHC.Types.D# [ds4_s1I0]; }; };
The final “lowered” version:
Foreign.it :: Foreign.C.Types.CDouble [GblId] = [] \u [] case ds_r1HA of { GHC.Types.D# ds2_s1HW [Occ=Once] -> case __pkg_ccall_GC main [ds2_s1HW GHC.Prim.realWorld#] of { Unit# ds4_s1I0 [Occ=Once] -> GHC.Types.D# [ds4_s1I0]; }; };
Cheers!
Chris