# Changelog for the [`ghc-typelits-natnormalise`](http://hackage.haskell.org/package/ghc-typelits-natnormalise) package
## 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:
* ` + x ~ 2 + x ==> [ ~ 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*
* Add workaround for https://ghc.haskell.org/trac/ghc/ticket/10301
## 0.1 *March 30th 2015*
* Initial release