Monomorphism by annotation of type variables
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Introduce the reserved word monomo
for rendering type variables monomorphic:
primitive newIORef :: monomo a . a -> IO (IORef a)
Its use in the type signatures for such primitives would prevent the definition of polymorphic references in all contexts - the (abbreviated) canonical example of abuse:
let v = unsafeLocalState $ newIORef undefined in
do writeIORef v ("0" :: [Char])
n <- readIORef v
return (n + 1 :: Int)
...would cause a type error - the type of undefined
is also made monomorphic by the annotated type of newIORef
, resulting in the
type monomo a . IORef a
for v
, preventing its dual specialisation to IORef [Char]
and IORef Int
.
Definitions relying on the old behaviour would be modified to use, or replaced by new primitives.
For the moment, this proposal can be "emulated" using Haskell's type classes:
- module Monomo where
- import Prelude(Bool, Char, Double, Either, Float, Int, IO, Integer)
- import Prelude(Maybe, String)
- import Data.IORef(IORef)
- import Data.STRef(STRef)
- import Data.Time(UTCTime, NominalDiffTime, Day, TimeOfDay)
- import Data.Time(LocalTime, TimeZone, ZonedTime)
- import Data.Time(DiffTime)
- import Data.Time(UniversalTime)
- import Control.Monad.ST(ST)
- import System.Directory(XdgDirectory, XdgDirectoryList, Permissions)
- import System.IO(Handle, IOMode, BufferMode, SeekMode, HandlePosn)
- import System.IO(TextEncoding, Newline, NewlineMode)
- import GHC.Base(RealWorld)
- class Monomo a
- -- add suitable new instances as needed...
- instance Monomo Bool
- instance Monomo BufferMode
- instance Monomo Char
- instance Monomo Day
- instance Monomo DiffTime
- instance Monomo Double
- instance (Monomo a, Monomo b) => Monomo (Either a b)
- instance Monomo Float
- instance Monomo Handle
- instance Monomo HandlePosn
- instance Monomo Int
- instance Monomo Integer
- instance Monomo (IO a)
- instance Monomo IOMode
- instance Monomo LocalTime
- instance Monomo a => Monomo (IORef a)
- instance Monomo a => Monomo [a]
- instance Monomo a => Monomo (Maybe a)
- instance Monomo Newline
- instance Monomo NewlineMode
- instance Monomo NominalDiffTime
- instance Monomo Permissions
- instance Monomo RealWorld
- instance Monomo SeekMode
- instance Monomo (ST s a)
- instance Monomo a => Monomo (STRef s a)
- instance Monomo TextEncoding
- instance Monomo TimeOfDay
- instance Monomo TimeZone
- instance (Monomo a, Monomo b, Monomo c, Monomo d, Monomo e, Monomo f) => Monomo (a, b, c, d, e, f)
- instance (Monomo a, Monomo b, Monomo c, Monomo d, Monomo e) => Monomo (a, b, c, d, e)
- instance (Monomo a, Monomo b, Monomo c, Monomo d) => Monomo (a, b, c, d)
- instance (Monomo a, Monomo b, Monomo c) => Monomo (a, b, c)
- instance (Monomo a, Monomo b) => Monomo (a, b)
- instance Monomo ()
- instance Monomo UniversalTime
- instance Monomo UTCTime
- instance Monomo XdgDirectory
- instance Monomo XdgDirectoryList
- instance Monomo ZonedTime
See also:
Atravers 00:21, 7 January 2019 (UTC)