----------------------------------------------------------------------------- -- -- Pretty-printing TyThings -- -- (c) The GHC Team 2005 -- ----------------------------------------------------------------------------- {-# LANGUAGE CPP #-} module PprTyThing ( pprTyThing, pprTyThingInContext, pprTyThingLoc, pprTyThingInContextLoc, pprTyThingHdr, pprTypeForUser, pprFamInst ) where #include "HsVersions.h" import GhcPrelude import Type ( ArgFlag(..), TyThing(..), mkTyVarBinders, pprUserForAll ) import IfaceSyn ( ShowSub(..), ShowHowMuch(..), AltPpr(..) , showToHeader, pprIfaceDecl ) import CoAxiom ( coAxiomTyCon ) import HscTypes( tyThingParent_maybe ) import MkIface ( tyThingToIfaceDecl ) import Type ( tidyOpenType ) import FamInstEnv( FamInst(..), FamFlavor(..) ) import Type( Type, pprTypeApp, pprSigmaType ) import Name import VarEnv( emptyTidyEnv ) import Outputable -- ----------------------------------------------------------------------------- -- Pretty-printing entities that we get from the GHC API {- Note [Pretty printing via IfaceSyn] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Our general plan for prett-printing - Types - TyCons - Classes - Pattern synonyms ...etc... is to convert them to IfaceSyn, and pretty-print that. For example - pprType converts a Type to an IfaceType, and pretty prints that. - pprTyThing converts the TyThing to an IfaceDecl, and pretty prints that. So IfaceSyn play a dual role: - it's the internal version of an interface files - it's used for pretty-printing Why do this? * A significant reason is that we need to be able to pretty-print IfaceSyn (to display Foo.hi), and it was a pain to duplicate masses of pretty-printing goop, esp for Type and IfaceType. * When pretty-printing (a type, say), we want to tidy (with tidyType) to avoids having (forall a a. blah) where the two a's have different uniques. Alas, for type constructors, TyCon, tidying does not work well, because a TyCon includes DataCons which include Types, which mention TyCons. And tidying can't tidy a mutually recursive data structure graph, only trees. * Interface files contains fast-strings, not uniques, so the very same tidying must take place when we convert to IfaceDecl. E.g. MkIface.tyThingToIfaceDecl which converts a TyThing (i.e. TyCon, Class etc) to an IfaceDecl. Bottom line: IfaceDecls are already 'tidy', so it's straightforward to print them. * An alternative I once explored was to ensure that TyCons get type variables with distinct print-names. That's ok for type variables but less easy for kind variables. Processing data type declarations is already so complicated that I don't think it's sensible to add the extra requirement that it generates only "pretty" types and kinds. Consequences: - IfaceSyn (and IfaceType) must contain enough information to print nicely. Hence, for example, the IfaceAppArgs type, which allows us to suppress invisible kind arguments in types (see Note [Suppressing invisible arguments] in IfaceType) - In a few places we have info that is used only for pretty-printing, and is totally ignored when turning IfaceSyn back into TyCons etc (in TcIface). For example, IfaceClosedSynFamilyTyCon stores a [IfaceAxBranch] that is used only for pretty-printing. - See Note [Free tyvars in IfaceType] in IfaceType See #7730, #8776 for details -} -------------------- -- | Pretty-prints a 'FamInst' (type/data family instance) with its defining location. pprFamInst :: FamInst -> SDoc -- * For data instances we go via pprTyThing of the representational TyCon, -- because there is already much cleverness associated with printing -- data type declarations that I don't want to duplicate -- * For type instances we print directly here; there is no TyCon -- to give to pprTyThing -- -- FamInstEnv.pprFamInst does a more quick-and-dirty job for internal purposes pprFamInst (FamInst { fi_flavor = DataFamilyInst rep_tc }) = pprTyThingInContextLoc (ATyCon rep_tc) pprFamInst (FamInst { fi_flavor = SynFamilyInst, fi_axiom = axiom , fi_tvs = tvs, fi_tys = lhs_tys, fi_rhs = rhs }) = showWithLoc (pprDefinedAt (getName axiom)) $ hang (text "type instance" <+> pprUserForAll (mkTyVarBinders Specified tvs) -- See Note [Printing foralls in type family instances] -- in IfaceType <+> pprTypeApp (coAxiomTyCon axiom) lhs_tys) 2 (equals <+> ppr rhs) ---------------------------- -- | Pretty-prints a 'TyThing' with its defining location. pprTyThingLoc :: TyThing -> SDoc pprTyThingLoc tyThing = showWithLoc (pprDefinedAt (getName tyThing)) (pprTyThing showToHeader tyThing) -- | Pretty-prints the 'TyThing' header. For functions and data constructors -- the function is equivalent to 'pprTyThing' but for type constructors -- and classes it prints only the header part of the declaration. pprTyThingHdr :: TyThing -> SDoc pprTyThingHdr = pprTyThing showToHeader -- | Pretty-prints a 'TyThing' in context: that is, if the entity -- is a data constructor, record selector, or class method, then -- the entity's parent declaration is pretty-printed with irrelevant -- parts omitted. pprTyThingInContext :: ShowSub -> TyThing -> SDoc pprTyThingInContext show_sub thing = go [] thing where go ss thing = case tyThingParent_maybe thing of Just parent -> go (getOccName thing : ss) parent Nothing -> pprTyThing (show_sub { ss_how_much = ShowSome ss (AltPpr Nothing) }) thing -- | Like 'pprTyThingInContext', but adds the defining location. pprTyThingInContextLoc :: TyThing -> SDoc pprTyThingInContextLoc tyThing = showWithLoc (pprDefinedAt (getName tyThing)) (pprTyThingInContext showToHeader tyThing) -- | Pretty-prints a 'TyThing'. pprTyThing :: ShowSub -> TyThing -> SDoc -- We pretty-print 'TyThing' via 'IfaceDecl' -- See Note [Pretty-printing TyThings] pprTyThing ss ty_thing = pprIfaceDecl ss' (tyThingToIfaceDecl ty_thing) where ss' = case ss_how_much ss of ShowHeader (AltPpr Nothing) -> ss { ss_how_much = ShowHeader ppr' } ShowSome xs (AltPpr Nothing) -> ss { ss_how_much = ShowSome xs ppr' } _ -> ss ppr' = AltPpr $ ppr_bndr $ getName ty_thing ppr_bndr :: Name -> Maybe (OccName -> SDoc) ppr_bndr name | isBuiltInSyntax name = Nothing | otherwise = case nameModule_maybe name of Just mod -> Just $ \occ -> getPprStyle $ \sty -> pprModulePrefix sty mod occ <> ppr occ Nothing -> WARN( True, ppr name ) Nothing -- Nothing is unexpected here; TyThings have External names pprTypeForUser :: Type -> SDoc -- The type is tidied pprTypeForUser ty = pprSigmaType tidy_ty where (_, tidy_ty) = tidyOpenType emptyTidyEnv ty -- Often the types/kinds we print in ghci are fully generalised -- and have no free variables, but it turns out that we sometimes -- print un-generalised kinds (eg when doing :k T), so it's -- better to use tidyOpenType here showWithLoc :: SDoc -> SDoc -> SDoc showWithLoc loc doc = hang doc 2 (char '\t' <> comment <+> loc) -- The tab tries to make them line up a bit where comment = text "--"