#14718: Add Boolean type families to 'base' package -------------------------------------+------------------------------------- Reporter: chshersh | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: Core Libraries | Version: 8.5 Resolution: | Keywords: base, type | families, Bool Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Description changed by chshersh: Old description:
Sometimes you want type families to perform type level computation with booleans. Specifically: {{{#!hs type family If (p :: Bool) (ifTrue :: k) (ifFalse :: k) :: k where ... type family (a :: Bool) && (b :: Bool) :: Bool where ... type family (a :: Bool) || (b :: Bool) :: Bool where ... type family Not (a :: Bool) :: Bool where }}}
Similar to existing module [https://hackage.haskell.org/package/base-4.10.1.0/docs/Data-Bool.html Data.Bool] in `base` package for boolean expressions.
There's not a single package with such type families for type-level boolean computations. Even if it exists it probably would very small. And as a library author you probably don't wan extra dependencies for your package because cost of adding new dependency for your project is much bigger than cost of adding module to existing dependencies (if it's possible of course).
It seems to me that such operations are kinda basic. And they just promote behavior of already existed expression-level functions to type level. And we already have type families for `Integer`, `Natural` and `String` (aka `Symbol`) and several type families returning `Bool` (`==`, `<=?`) in `base`. So I propose to add couple useful utilities to operate with `Bool` explicitly.
New description: Sometimes you want type families to perform type level computation with booleans. Specifically: {{{#!hs type family If (p :: Bool) (ifTrue :: k) (ifFalse :: k) :: k where ... type family (a :: Bool) && (b :: Bool) :: Bool where ... type family (a :: Bool) || (b :: Bool) :: Bool where ... type family Not (a :: Bool) :: Bool where }}} Similar to existing module [https://hackage.haskell.org/package/base-4.10.1.0/docs/Data-Bool.html Data.Bool] in `base` package for boolean expressions. There's not a single package with such type families for type-level boolean computations. Even if it exists it probably would very small. And as a library author you probably don't wan extra dependencies for your package because cost of adding new dependency for your project is much bigger than cost of adding module to existing dependencies (if it's possible of course). It seems to me that such operations are kinda basic. And they just promote behavior of already existed expression-level functions to type level. And we already have type families for `Integer`, `Natural` and `String` (aka `Symbol`) and several type families returning `Bool` (`==`, `<=?`) in `base`. So I propose to add couple useful utilities to operate with `Bool` explicitly. If this proposal approved I'm willing to contribute to `ghc`! -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14718#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler