abstractly-keyed-implicits (empty) → 0.1.0.0
raw patch · 4 files changed
+317/−0 lines, 4 filesdep +base
Dependencies added: base
Files
- CHANGELOG.md +5/−0
- Data/Implicit.hs +74/−0
- LICENSE +202/−0
- abstractly-keyed-implicits.cabal +36/−0
+ CHANGELOG.md view
@@ -0,0 +1,5 @@+# Revision history for abstractly-keyed-implicits++## 0.1.0.0 -- 2025-12-25++* Fully implement proposal
+ Data/Implicit.hs view
@@ -0,0 +1,74 @@+{-# LANGUAGE DataKinds #-}+{-# LANGUAGE RequiredTypeArguments #-}+{-# LANGUAGE Trustworthy #-}+{-# LANGUAGE TypeFamilies #-}++-- |+-- Description : Manage the implicit parameter namespace dynamically at compile time.+-- Copyright : Copyright 2025 Shea Levy+-- License : Apache-2.0+-- Maintainer : shea@shealevy.com+--+-- Manage the implicit parameter namespace dynamically at compile time.+--+-- This is an implementation of [GHC proposal 737](https://github.com/ghc-proposals/ghc-proposals/pull/737).+-- Relative to that proposal, this suffers from the following (likely hypothetical) limitations:+--+-- * It may break if future GHC versions change the implementation of implicit parameters+-- * It doesn't mandate that 'bindImplicit' and 'implicitParameter' be fully applied,+-- nor guarantee that they don't impose additional runtime cost.+-- * It uses some auxiliary internal type-level machinery that can't be hidden.+-- * It is not inferred as safe Haskell (though it is safe).+module Data.Implicit where++import GHC.Base (IP, ip, withDict)+import GHC.TypeLits (Symbol)++-- | 'ImplicitParameter' @x@ @a@ is a t'Data.Kind.Constraint' that 'implicitParameter' @x@ is an implicit parameter of type @a@.+--+-- 'ImplicitParameter' constraints are propagated according to dynamic scoping rules.+-- In other words, GHC always takes the most nested parameter binding from the context+-- to find the value. @bindImplict x a (bindImplict x b (implicitParameter x))@+-- is equivalent to @b@ (including resulting in a type error if used where+-- a term whose type unifies with @a@'s but not @b@'s is expected).+--+-- To bind an implicit parameter, use 'bindImplicit'.+--+-- @ImplictParameter (MkIdent "foo") t@ is equivalent to @?foo :: t@.+type ImplicitParameter (x :: k) = IP (KeyName x)++-- | Bind implicit parameter @x@ to the provided @a@.+--+-- @bindImplicit (MkIdent "foo") x go@ is equivalent to @let ?foo = x in go@.+{-# INLINE bindImplicit #-}+bindImplicit :: forall x -> a -> ((ImplicitParameter x a) => b) -> b+bindImplicit _ = withDict++-- | Access implicit parameter bound to @x@.+--+-- @implicitParameter (MkIdent "foo")@ is equivalent to @?foo@.+{-# INLINE implicitParameter #-}+implicitParameter :: forall x -> (ImplicitParameter x a) => a+implicitParameter x = ip @(KeyName x)++-- | The kind of type-level representations of Haskell identifiers.+data Ident = MkIdent Symbol {- HLINT ignore "Use newtype instead of data" -}++-- | The identifier's name+type family IdentName (i :: Ident) :: Symbol where+ IdentName (MkIdent s) = s++-- *** Implementation details++-- | Helper data family to create a new 'Symbol' from a type-level value of any kind.+data family MkSymbol (t :: k) :: k'++-- | Turn the key of an 'ImplicitParameter' into a 'Symbol' for GHC's 'IP' type class.+--+-- 'Ident' ifiers are directly mapped to their underlying names.+--+-- Other type-level values are injected into 'Symbol' via 'MkSymbol'.+type KeyName :: forall k. k -> Symbol+type family KeyName t where+ KeyName i = IdentName i+ KeyName t = MkSymbol t
+ LICENSE view
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+ abstractly-keyed-implicits.cabal view
@@ -0,0 +1,36 @@+cabal-version: 3.0+name: abstractly-keyed-implicits+version: 0.1.0.0+synopsis: Manage the implicit parameter namespace dynamically at compile time.+description:+ Manage the implicit parameter namespace dynamically at compile time.++ This is an implementation of [GHC proposal 737](https://github.com/ghc-proposals/ghc-proposals/pull/737).+ Relative to that proposal, this suffers from the following (likely hypothetical) limitations:++ * It may break if future GHC versions change the implementation of implicit parameters+ * It doesn't mandate that 'bindImplicit' and 'implicitParameter' be fully applied,+ nor guarantee that they don't impose additional runtime cost.+ * It uses some auxiliary internal type-level machinery that can't be hidden.+ * It is not inferred as safe Haskell (though it is safe).+homepage: https://github.com/shlevy/shlevy/tree/master/abstractly-keyed-implicits+bug-reports: https://github.com/shlevy/shlevy/issues+license: Apache-2.0+license-file: LICENSE+author: Shea Levy+maintainer: shea@shealevy.com+copyright: Copyright 2025 Shea Levy+category: Data+build-type: Simple+extra-doc-files: CHANGELOG.md+tested-with: GHC == { 9.10.2, 9.12.2 }++source-repository head+ type: git+ location: https://github.com/shlevy/shlevy+ subdir: abstractly-keyed-implicits++library+ exposed-modules: Data.Implicit+ build-depends: base ^>= { 4.20, 4.21 }+ default-language: GHC2024