singletons-2.4: src/Data/Singletons/Deriving/Show.hs
-----------------------------------------------------------------------------
-- |
-- Module : Data.Singletons.Deriving.Show
-- Copyright : (C) 2017 Ryan Scott
-- License : BSD-style (see LICENSE)
-- Maintainer : Richard Eisenberg (rae@cs.brynmawr.edu)
-- Stability : experimental
-- Portability : non-portable
--
-- Implements deriving of Show instances
--
----------------------------------------------------------------------------
{-# LANGUAGE ScopedTypeVariables #-}
module Data.Singletons.Deriving.Show (
mkShowInstance
, ShowMode(..)
, mkShowContext
) where
import Language.Haskell.TH.Syntax hiding (showName)
import Language.Haskell.TH.Desugar
import Data.Singletons.Names
import Data.Singletons.Util
import Data.Singletons.Syntax
import Data.Singletons.Deriving.Infer
import Data.Maybe (fromMaybe)
import GHC.Lexeme (startsConSym, startsVarSym)
import GHC.Show (appPrec, appPrec1)
mkShowInstance :: DsMonad q
=> ShowMode -> Maybe DCxt -> DType -> [DCon]
-> q UInstDecl
mkShowInstance mode mb_ctxt ty cons = do
clauses <- mk_showsPrec mode cons
constraints <- inferConstraintsDef (fmap (mkShowContext mode) mb_ctxt)
(DConPr (mk_Show_name mode))
ty cons
return $ InstDecl { id_cxt = constraints
, id_name = mk_Show_name mode
, id_arg_tys = [ty]
, id_meths = [ (mk_showsPrec_name mode, UFunction clauses) ] }
mk_showsPrec :: DsMonad q => ShowMode -> [DCon] -> q [DClause]
mk_showsPrec mode cons = do
p <- newUniqueName "p" -- The precedence argument (not always used)
if null cons
then do v <- newUniqueName "v"
pure [DClause [DWildPa, DVarPa v] (DCaseE (DVarE v) [])]
else mapM (mk_showsPrec_clause mode p) cons
mk_showsPrec_clause :: forall q. DsMonad q
=> ShowMode -> Name -> DCon
-> q DClause
mk_showsPrec_clause mode p (DCon _ _ con_name con_fields _) = go con_fields
where
con_name' :: Name
con_name' = case mode of
ForPromotion -> con_name
ForShowSing -> singDataConName con_name
go :: DConFields -> q DClause
-- No fields: print just the constructor name, with no parentheses
go (DNormalC _ []) = return $
DClause [DWildPa, DConPa con_name' []] $
DVarE showStringName `DAppE` dStringE (parenInfixConName con_name' "")
-- Infix constructors have special Show treatment.
go (DNormalC True tys@[_, _])
-- Although the (:) constructor is infix, its singled counterpart SCons
-- is not, which matters if we're deriving a ShowSing instance.
-- Unless we remove this special case (see #234), we will simply
-- shunt it along as if we were dealing with a prefix constructor.
| ForShowSing <- mode
, con_name == consName
= go (DNormalC False tys)
| otherwise
= do argL <- newUniqueName "argL"
argR <- newUniqueName "argR"
fi <- fromMaybe defaultFixity <$> reifyFixityWithLocals con_name'
let con_prec = case fi of Fixity prec _ -> prec
op_name = nameBase con_name'
infixOpE = DAppE (DVarE showStringName) . dStringE $
if isInfixDataCon op_name
then " " ++ op_name ++ " "
-- Make sure to handle infix data constructors
-- like (Int `Foo` Int)
else " `" ++ op_name ++ "` "
return $ DClause [DVarPa p, DConPa con_name' [DVarPa argL, DVarPa argR]] $
(DVarE showParenName `DAppE` (DVarE gtName `DAppE` DVarE p
`DAppE` dIntegerE con_prec))
`DAppE` (DVarE composeName
`DAppE` showsPrecE mode (con_prec + 1) argL
`DAppE` (DVarE composeName
`DAppE` infixOpE
`DAppE` showsPrecE mode (con_prec + 1) argR))
go (DNormalC _ tys) = do
args <- mapM (const $ newUniqueName "arg") tys
let show_args = map (showsPrecE mode appPrec1) args
composed_args = foldr1 (\v q -> DVarE composeName
`DAppE` v
`DAppE` (DVarE composeName
`DAppE` DVarE showSpaceName
`DAppE` q)) show_args
named_args = DVarE composeName
`DAppE` (DVarE showStringName
`DAppE` dStringE (parenInfixConName con_name' " "))
`DAppE` composed_args
return $ DClause [DVarPa p, DConPa con_name' $ map DVarPa args] $
DVarE showParenName
`DAppE` (DVarE gtName `DAppE` DVarE p `DAppE` dIntegerE appPrec)
`DAppE` named_args
-- We show a record constructor with no fields the same way we'd show a
-- normal constructor with no fields.
go (DRecC []) = go (DNormalC False [])
go (DRecC tys) = do
args <- mapM (const $ newUniqueName "arg") tys
let show_args =
concatMap (\((arg_name, _, _), arg) ->
let arg_name' = case mode of
ForPromotion -> arg_name
ForShowSing -> singValName arg_name
arg_nameBase = nameBase arg_name'
infix_rec = showParen (isSym arg_nameBase)
(showString arg_nameBase) ""
in [ DVarE showStringName `DAppE` dStringE (infix_rec ++ " = ")
, showsPrecE mode 0 arg
, DVarE showCommaSpaceName
])
(zip tys args)
brace_comma_args = (DVarE showCharName `DAppE` dCharE mode '{')
: take (length show_args - 1) show_args
composed_args = foldr (\x y -> DVarE composeName `DAppE` x `DAppE` y)
(DVarE showCharName `DAppE` dCharE mode '}')
brace_comma_args
named_args = DVarE composeName
`DAppE` (DVarE showStringName
`DAppE` dStringE (parenInfixConName con_name' " "))
`DAppE` composed_args
return $ DClause [DVarPa p, DConPa con_name' $ map DVarPa args] $
DVarE showParenName
`DAppE` (DVarE gtName `DAppE` DVarE p `DAppE` dIntegerE appPrec)
`DAppE` named_args
-- | Parenthesize an infix constructor name if it is being applied as a prefix
-- function (e.g., data Amp a = (:&) a a)
parenInfixConName :: Name -> ShowS
parenInfixConName conName =
let conNameBase = nameBase conName
in showParen (isInfixDataCon conNameBase) $ showString conNameBase
showsPrecE :: ShowMode -> Int -> Name -> DExp
showsPrecE mode prec n = DVarE (mk_showsPrec_name mode) `DAppE` dIntegerE prec `DAppE` DVarE n
dCharE :: ShowMode -> Char -> DExp
dCharE mode = DLitE . to_lit
where
to_lit :: Char -> Lit
to_lit c = case mode of
ForPromotion -> StringL [c] -- There aren't type-level characters yet,
-- so fake it with a string
ForShowSing -> CharL c
dStringE :: String -> DExp
dStringE = DLitE . StringL
dIntegerE :: Int -> DExp
dIntegerE = DLitE . IntegerL . fromIntegral
isSym :: String -> Bool
isSym "" = False
isSym (c : _) = startsVarSym c || startsConSym c
-----
-- ShowMode
-----
-- | Is a 'Show' instance being generated to be promoted/singled, or is it
-- being generated to create a @ShowSing@/'Show' instance for a singleton type?
data ShowMode = ForPromotion -- ^ For promotion/singling
| ForShowSing -- ^ For a @ShowSing@/'Show' instance
-- | Turn a context like @('Show' a, 'Show' b)@ into @('ShowSing' a, 'ShowSing' b)@.
-- This is necessary for standalone-derived instances.
mkShowContext :: ShowMode -> DCxt -> DCxt
mkShowContext ForPromotion = id
mkShowContext ForShowSing = map show_to_SingShow
where
show_to_SingShow :: DPred -> DPred
show_to_SingShow = modifyConNameDPred $ \n ->
if n == showName
then showSingName
else n
mk_Show_name :: ShowMode -> Name
mk_Show_name ForPromotion = showName
mk_Show_name ForShowSing = showSingName
mk_showsPrec_name :: ShowMode -> Name
mk_showsPrec_name ForPromotion = showsPrecName
mk_showsPrec_name ForShowSing = showsSingPrecName