haskell-holes-th: Infer haskell code by given type.

This is a package candidate release! Here you can preview how this package release will appear once published to the main package index (which can be accomplished via the 'maintain' link below). Please note that once a package has been published to the main package index it cannot be undone! Please consult the package uploading documentation for more information.

[maintain] [Publish]

TIP solver for simply typed lambda calculus to automatically infer the code from type definitions using TemplateHaskell.

[Skip to Readme]

Properties

Versions	0.0.0.1, 1.0.0.0, 1.0.0.0, 2.0.0.0
Change log	None available
Dependencies	base (>=4.9 && <4.10), template-haskell (>=2.11 && <2.12) [details]
License	MIT
Author	klntsky
Maintainer	klntsky@gmail.com
Category	Language
Home page	https://github.com/8084/haskell-holes-th
Source repo	head: git clone git://github.com/8084/haskell-holes-th.git
Uploaded	by klntsky at 2017-12-10T01:15:04Z

Modules

[Index]

Language
- Haskell
  - Language.Haskell.Holes

Downloads

haskell-holes-th-1.0.0.0.tar.gz [browse] (Cabal source package)
Package description (as included in the package)

Maintainer's Corner

Package maintainers

klntsky

For package maintainers and hackage trustees

edit package information

Readme for haskell-holes-th-1.0.0.0

[back to package description]

haskell-holes-th

TIP solver for simply typed lambda calculus to automatically infer the code from type definitions using TemplateHaskell. It may also be viewed as a prover for intuitionistic propositional logic with only implication allowed.

Usage

The following example shows the basic usage of the macro.

{-# LANGUAGE TemplateHaskell #-}

import Language.Haskell.Holes

-- \x -> x
i :: a -> a
i = $(hole [| I :: a -> a |])

-- \x y -> x y y
w :: (a -> a -> b) -> a -> b
w = $(hole [| W :: (a -> a -> b) -> a -> b |])

-- \x y z -> x (y z)
b :: (b -> c) -> (a -> b) -> (a -> c)
b = $(hole [| B :: (b -> c) -> (a -> b) -> (a -> c) |])

-- \x y z -> x z y
c :: (a -> b -> c) -> (b -> a -> c)
c = $(hole [| C :: (a -> b -> c) -> (b -> a -> c) |])

Also check out Test.hs.

Limitations

Only atomic types from the given context can be inferred. Use holeWith instead of hole to specify a non-default context. The default one contains Bool, Char, Double, Float, Int, Integer, Word and String.
Haskell's type system is more rich than simply typed lambda calculus (it allows polymorphism), so some of the types that have corresponding definitions in Haskell can't be inferred. Also, in STLC every typed term is strongly normalizing, so the type of fixed-point combinator can't be inhabited.

Custom context

Any atomic type can be added to the context by constructing a quoted expression of that type and a type itself (as an Exp from TemplateHaskell).

t3 :: Maybe Int
t3 = $(holeWith
       -- context = [Just 0 :: Maybe Int]
       [([| Just 0 |], AppT (ConT ''Maybe) (ConT ''Int))]
       [| mi :: Maybe Int |])

If the type do not correspond to the quoted value, the code containing the inferred term will not compile, but no warnings or errors will be shown if the quoted value is never used.

Type definition in terms of Exp can be retrieved from ghci as follows:

$ ghci -XTemplateHaskell
Prelude> :m + Language.Haskell.TH
Prelude Language.Haskell.TH> runQ [| _ :: Either (Maybe Int) String |] >>= print
SigE (UnboundVarE _) (AppT (AppT (ConT Data.Either.Either) (AppT (ConT GHC.Base.Maybe) (ConT GHC.Types.Int))) (ConT GHC.Base.String))

The part starting after (UnboundVarE _) is needed.

Notes

Type unification is not implemented, but it may be added in the future.