ghc-typelits-natnormalise

GHC typechecker plugin for types of kind GHC.TypeLits.Nat

http://www.clash-lang.org/

Version on this page:0.4
LTS Haskell 24.18:0.7.10
Stackage Nightly 2025-11-04:0.9.1
Latest on Hackage:0.9.1

See all snapshots ghc-typelits-natnormalise appears in

BSD-2-Clause licensed by Christiaan Baaij
Maintained by [email protected]
This version can be pinned in stack with:ghc-typelits-natnormalise-0.4@sha256:e4db76ab525baa3396c5dcc9bf6b5835f0460bdf7171c29d4818c1c2239b3e52,2966

Module documentation for 0.4

Used by 2 packages in nightly-2016-01-29(full list with versions):
clash-ghc, clash-prelude

ghc-tynat-normalise

Build Status Hackage Hackage Dependencies

A type checker plugin for GHC that can solve equalities of types of kind Nat, where these types are either:

  • Type-level naturals
  • Type variables
  • Applications of the arithmetic expressions (+,-,*,^).

It solves these equalities by normalising them to sort-of SOP (Sum-of-Products) form, and then perform a simple syntactic equality.

For example, this solver can prove the equality between:

(x + 2)^(y + 2)

and

4*x*(2 + x)^y + 4*(2 + x)^y + (2 + x)^y*x^2

Because the latter is actually the SOP normal form of the former.

To use the plugin, add

{-# OPTIONS_GHC -fplugin GHC.TypeLits.Normalise #-}

To the header of your file.

Changes

Changelog for the ghc-typelits-natnormalise package

0.4 January 19th 2016

  • Stop using ‘provenance’ hack to create conditional evidence (GHC 8.0+ only)
  • Find more unifications:
    • F x + 2 - 1 - 1 ~ F x ==> [F x := F x], where F can be any type function with result Nat.

0.3.2

  • Find more unifications:
    • (z ^ a) ~ (z ^ b) ==> [a := b]
    • (i ^ a) ~ j ==> [a := round (logBase i j)], when i and j are integers, and ceiling (logBase i j) == floor (logBase i j).

0.3.1 October 19th 2015

  • Find more unifications:
    • (i * a) ~ j ==> [a := div j i], when i and j are integers, and mod j i == 0.
    • (i * a) + j ~ k ==> [a := div (k-j) i], when i, j, and k are integers, and k-j >= 0 and mod (k-j) i == 0.

0.3 June 3rd 2015

  • Find more unifications:
    • <TyApp xs> + x ~ 2 + x ==> [<TyApp xs> ~ 2]
  • Fixes bugs:
    • Unifying a*b ~ b now returns [a ~ 1]; before it erroneously returned [a ~ ], which is interpred as [a ~ 0]…
    • Unifying a+b ~ b now returns [a ~ 0]; before it returned the undesirable, though equal, [a ~ ]

0.2.1 May 6th 2015

  • Update Eq instance of SOP: Empty SOP is equal to 0

0.2 April 22nd 2015

  • Finds more unifications:
    • (2 + a) ~ 5 ==> [a := 3]
    • (3 * a) ~ 0 ==> [a := 0]

0.1.2 April 21st 2015

  • Don’t simplify expressions with negative exponents

0.1.1 April 17th 2015

0.1 March 30th 2015

  • Initial release