tagToEnum# annotations in AlexWrapper C macros for -XImpredicativeTypes #278
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NadiaYvette
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The various force pushes are for build errors of my handwritten testcase with elder |
andreasabel
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tests/monadic_expr.x
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| Left e -> fail e | ||
| Right (n, txt) | ||
| | Text.null txt -> pure $ TokenInt n | ||
| | otherwise -> fail "got incomplete prefix " } |
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For GHC 8.4/8.6: fail -> Control.Monad.Fail.fail (or hidefail from Control.Monad).
In general, just using explicit imports makes things more robust across multiple GHC versions...
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Here is the whole (hi)story: https://gitlab.haskell.org/haskell/prime/-/wikis/libraries/proposals/monad-fail#transitional-strategy
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Covered, thanks! The force push hides this as part of the history, but it covers at least Control.Monad and Control.Monad.Fail with the explicit imports.
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It also comes in through Prelude; I'm just using it qualified now.
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With -XImpredicativeTypes, the following occurs:
basic_typeclass.i.hs:877:28: error: [GHC-36495]
• tagToEnum# must appear applied to one value argument
• In the first argument of ‘(&&)’, namely
‘(GHC.Exts.tagToEnum# (offset >=# 0#))’
In the expression:
(GHC.Exts.tagToEnum# (offset >=# 0#))
&&
let check = alexIndexInt16OffAddr alex_check offset
in (GHC.Exts.tagToEnum# (check ==# ord_c))
In the expression:
if (GHC.Exts.tagToEnum# (offset >=# 0#))
&&
let check = alexIndexInt16OffAddr alex_check offset
in (GHC.Exts.tagToEnum# (check ==# ord_c)) then
alexIndexInt16OffAddr alex_table offset
else
alexIndexInt16OffAddr alex_deflt s
|
877 | new_s = if GTE(offset,ILIT(0))
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
GTE() and EQ() were getting the following errors for the
monadUserState-strict-text and possibly other cases with
-XImpredicativeTypes enabled:
basic_typeclass.i.hs:877:28: error: [GHC-36495]
• tagToEnum# must appear applied to one value argument
• In the first argument of ‘(&&)’, namely
‘(GHC.Exts.tagToEnum# (offset >=# 0#))’
In the expression:
(GHC.Exts.tagToEnum# (offset >=# 0#))
&&
let check = alexIndexInt16OffAddr alex_check offset
in (GHC.Exts.tagToEnum# (check ==# ord_c))
In the expression:
if (GHC.Exts.tagToEnum# (offset >=# 0#))
&&
let check = alexIndexInt16OffAddr alex_check offset
in (GHC.Exts.tagToEnum# (check ==# ord_c)) then
alexIndexInt16OffAddr alex_table offset
else
alexIndexInt16OffAddr alex_deflt s
|
877 | new_s = if GTE(offset,ILIT(0))
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Annotating the tagToEnum# usage to specify which Enum is intended was
one case. Another was annotating the results of ==# and >=# to resolve
some ambiguity involved there.
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This is the fix mentioned for
Type inference on the unboxed types doesn't play so well with
-XImpredicativeTypes, so, after creating testcases for it (one new handwritten one and converting preexisting ones by just using the language extension flag), this branch adds type annotations within C macros used inAlexWrapper.hs.Closes #277.