diff options
Diffstat (limited to 'compiler/iface/IfaceSyn.hs')
| -rw-r--r-- | compiler/iface/IfaceSyn.hs | 35 |
1 files changed, 31 insertions, 4 deletions
diff --git a/compiler/iface/IfaceSyn.hs b/compiler/iface/IfaceSyn.hs index 05f64dff5a..dac3270482 100644 --- a/compiler/iface/IfaceSyn.hs +++ b/compiler/iface/IfaceSyn.hs @@ -47,6 +47,7 @@ import IfaceType import BinFingerprint import CoreSyn( IsOrphan, isOrphan ) import PprCore() -- Printing DFunArgs +import DynFlags( gopt, GeneralFlag (Opt_PrintAxiomIncomps) ) import Demand import Class import FieldLabel @@ -66,7 +67,7 @@ import Binary import BooleanFormula ( BooleanFormula, pprBooleanFormula, isTrue ) import Var( VarBndr(..), binderVar ) import TyCon ( Role (..), Injectivity(..), tyConBndrVisArgFlag ) -import Util( dropList, filterByList ) +import Util( dropList, filterByList, notNull ) import DataCon (SrcStrictness(..), SrcUnpackedness(..)) import Lexeme (isLexSym) @@ -545,6 +546,28 @@ to cross the separate compilation boundary. In general we retain all info that is left by CoreTidy.tidyLetBndr, since that is what is seen by importing module with --make +Note [Displaying axiom incompatibilities] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +With -fprint-axiom-incomps we display which closed type family equations +are incompatible with which. This information is sometimes necessary +because GHC doesn't try equations in order: any equation can be used when +all preceding equations that are incompatible with it do not apply. + +For example, the last "a && a = a" equation in Data.Type.Bool.&& is +actually compatible with all previous equations, and can reduce at any +time. + +This is displayed as: +Prelude> :i Data.Type.Equality.== +type family (==) (a :: k) (b :: k) :: Bool + where + (==) (f a) (g b) = (f == g) && (a == b) + (==) a a = 'True + -- incompatible indices: 0 + (==) _1 _2 = 'False + -- incompatible indices: 1, 0 +The comment after an equation refers to all previous equations (0-indexed) +that are incompatible with it. ************************************************************************ * * @@ -571,13 +594,17 @@ pprAxBranch pp_tc (IfaceAxBranch { ifaxbTyVars = tvs = WARN( not (null _cvs), pp_tc $$ ppr _cvs ) hang ppr_binders 2 (hang pp_lhs 2 (equals <+> ppr rhs)) $+$ - nest 2 maybe_incomps + nest 6 maybe_incomps where -- See Note [Printing foralls in type family instances] in IfaceType ppr_binders = pprUserIfaceForAll $ map (mkIfaceForAllTvBndr Specified) tvs pp_lhs = hang pp_tc 2 (pprParendIfaceAppArgs pat_tys) - maybe_incomps = ppUnless (null incomps) $ parens $ - text "incompatible indices:" <+> ppr incomps + + -- See Note [Displaying axiom incompatibilities] + maybe_incomps + = sdocWithDynFlags $ \dflags -> + ppWhen (gopt Opt_PrintAxiomIncomps dflags && notNull incomps) $ + text "--" <+> text "incompatible indices:" <+> interpp'SP incomps instance Outputable IfaceAnnotation where ppr (IfaceAnnotation target value) = ppr target <+> colon <+> ppr value |