# Changelog for the ghc-typelits-natnormalise package

## 0.7.3 January 1st 2021

• Build on GHC 9.0.1-rc1

## 0.7.2 March 9 2020

• Fixes #44 infinite loop due to boxed equality

## 0.7.1 February 6th 2020

• Add support for GHC 8.10.1-alpha2
• Fixes #23: Can't figure out + commutes in some contexts on GHC 8.6.3
• Fixes #28: Using the solver seems to break GHC
• Fixes #34: inequality solver mishandles subtraction

## 0.7 August 26th 2019

• Require KnownNat constraints when solving with constants

## 0.6.2 July 10th 2018

• Add support for GHC 8.6.1-alpha1
• Solve larger inequalities from smaller inequalities, e.g.
• a <= n implies a <= n + 1

## 0.6.1 May 9th 2018

• Stop solving x + y ~ a + b by asking GHC to solve x ~ a and y ~ b as this leads to a situation where we find a solution that is not the most general.
• Stop using the smallest solution to an inequality to solve an equality, as this leads to finding solutions that are not the most general.
• Solve smaller inequalities from larger inequalities, e.g.
• 1 <= 2*x implies 1 <= x
• x + 2 <= y implies x <= y and 2 <= y

## 0.6 April 23rd 2018

• Solving constraints with a-b will emit b <= a constraints. e.g. solving n-1+1 ~ n will emit a 1 <= n constraint.
• If you need subtraction to be treated as addition with a negated operarand run with -fplugin-opt GHC.TypeLits.Normalise:allow-negated-numbers, and the b <= a constraint won't be emitted. Note that doing so can lead to unsound behaviour.
• Try to solve equalities using smallest solution of inequalities:
• Solve x + 1 ~ y using 1 <= y => x + 1 ~ 1 => x ~ 0
• Solve inequalities using simple transitivity rules:
• 2 <= x implies 1 <= x
• x <= 9 implies x <= 10
• Solve inequalities using simple monotonicity of addition rules:
• 2 <= x implies 2 + 2*x <= 3*x
• Solve inequalities using simple monotonicity of multiplication rules:
• 1 <= x implies 1 <= 3*x
• Solve inequalities using simple monotonicity of exponentiation rules:
• 1 <= x implies 2 <= 2^x
• Solve inequalities using powers of 2 and monotonicity of exponentiation:
• 2 <= x implies 2^(2 + 2*x) <= 2^(3*x)

## 0.5.10 April 15th 2018

• Add support for GHC 8.5.20180306

## 0.5.9 March 17th 2018

• Add support for GHC 8.4.1

## 0.5.8 January 4th 2018

• Add support for GHC 8.4.1-alpha1

## 0.5.7 November 7th 2017

• Solve inequalities such as: 1 <= a + 3

## 0.5.6 October 31st 2017

• Fixes bugs:
• (x + 1) ~ (2 * y) no longer implies ((2 * (y - 1)) + 1) ~ x

## 0.5.5 October 22nd 2017

• Solve inequalities when their normal forms are the same, i.e.
• (2 <= (2 ^ (n + d))) implies (2 <= (2 ^ (d + n)))
• Find more unifications:
• 8^x - 2*4^x ~ 8^y - 2*4^y ==> [x := y]

## 0.5.4 October 14th 2017

• Perform normalisations such as: 2^x * 4^x ==> 8^x

## 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 March 30th 2015

• Initial release