ghc-typelits-natnormalise

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

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

Version on this page:0.5.3
LTS Haskell 23.27:0.7.10
Stackage Nightly 2025-07-07:0.7.10
Latest on Hackage:0.7.11

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-0.5.3@sha256:e38c30980aaba3b89bd077edab7871e378aaa69ce013a92b97e056a8e0a0e71f,3108

Module documentation for 0.5.3

ghc-typelits-natnormalise

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

0.5.3 May 15th 2017

  • Add support for GHC 8.2

0.5.2 January 15th 2017

  • Fixes bugs:
    • Reification from SOP to Type sometimes loses product terms

0.5.1 September 29th 2016

  • Fixes bugs:
    • Cannot solve an equality for the second time in a definition group

0.5 August 17th 2016

  • Solve simple inequalities, i.e.:
    • a <= a + 1
    • 2a <= 3a
    • 1 <= a^b

0.4.6 July 21th 2016

  • Reduce “x^(-y) * x^y” to 1
  • Fixes bugs:
    • Subtraction in exponent induces infinite loop

0.4.5 July 20th 2016

  • Fixes bugs:
    • Reifying negative exponent causes GHC panic

0.4.4 July 19th 2016

  • Fixes bugs:
    • Rounding error in logBase calculation

0.4.3 July 18th 2016

  • Fixes bugs:
    • False positive: “f :: (CLog 2 (2 ^ n) ~ n, (1 <=? n) ~ True) => Proxy n -> Proxy (n+d)”

0.4.2 July 8th 2016

  • Find more unifications:
    • (2*e ^ d) ~ (2*e*a*c) ==> [a*c := 2*e ^ (d-1)]
    • a^d * a^e ~ a^c ==> [c := d + e]
    • x+5 ~ y ==> [x := y - 5], but only when x+5 ~ y is a given constraint

0.4.1 February 4th 2016

  • Find more unifications:
    • F x y k z ~ F x y (k-1+1) z ==> [k := k], where F can be any type function

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