BSD-2-Clause licensed by Christiaan Baaij
This version can be pinned in stack with:ghc-typelits-natnormalise-0.4.2@sha256:350d79d657dacdb06ef2e9843d907646210d292a805d4c9befc8542058c74e56,2968
Module documentation for 0.4.2
ghc-typelits-natnormalise
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.
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
