[GHC] #16178: Brackets and splices should be overloaded like the static keyword
#16178: Brackets and splices should be overloaded like the static keyword -------------------------------------+------------------------------------- Reporter: mpickering | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Template | Version: 8.6.3 Haskell | Keywords: | Operating System: Unknown/Multiple TypedTemplateHaskell | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- It's quite convenient that the `static` keyword is rebindable. To recap, if `e :: T` then `static e :: (IsStatic p) => p t`. It should also be possible rebind brackets and splices in the same manner. So we introduce two type classes `IsBracket` and `IsSplice`. Now quoting a term `e :: T` has type `e :: IsBracket p => p T` and the argument to a splice must have type `e :: IsSplice p => p T` which results in a value of type `T`. {{{ class IsBracket p where fromBracket :: Code t -> p t class IsSplice p where toBracket :: p t -> Code t foo :: IsBracket p => p Int foo = [|| 5 ||] qux :: (IsSplice p, IsBracket p) => Int qux = $$(foo) }}} As an aside, arguably the `static` form should only be rebindable when `RebindableSyntax` is enabled but that boat seems to have sailed. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16178 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#16178: Brackets and splices should be overloaded like the static keyword -------------------------------------+------------------------------------- Reporter: mpickering | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: Template Haskell | Version: 8.6.3 Resolution: | Keywords: | TypedTemplateHaskell Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Could you give some examples of how this new ability would be useful? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16178#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#16178: Brackets and splices should be overloaded like the static keyword -------------------------------------+------------------------------------- Reporter: mpickering | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: Template Haskell | Version: 8.6.3 Resolution: | Keywords: | TypedTemplateHaskell Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by mpickering): If you define a partially static monoid type such as the following which tries to evaluate as many concatenations statically as possible. {{{ data PS a = Static a | Dynamic (Code a) instance Monoid a => Monoid (PS a) where mempty = Static mempty (Static a) <> (Static b) = Static (a <> b) -- Using the overloading here a <> c = [|| $$a <> $$c ||] lower :: Lift a => PS a -> Code a lower (Static a) = lift a lower (Dynamic c) = c instance IsSplice PS where toBracket = lower instance IsBracket PS where fromBracket = Dynamic sta :: a -> PS a sta = Static }}} Writing programs with this data type becomes much more pleasant as the additional lifting and lowering become transparent. You can combine together these layers multiple times to implicitly perform different rewritings but the client's splice will still end up looking the same. {{{ prog = (sta () <> sta ()) <> [|| () ||] }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16178#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#16178: Brackets and splices should be overloaded like the static keyword -------------------------------------+------------------------------------- Reporter: mpickering | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: Template Haskell | Version: 8.6.3 Resolution: | Keywords: | TypedTemplateHaskell Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by goldfire): This seems like something which should go through the normal proposals process... -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16178#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
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