singleton-typelits
Version 0.1.0.0 revision 0 uploaded by mniip.
Package meta
- Synopsis
- Singletons and induction over GHC TypeLits
- Description
Singletons and induction schemes over GHC.TypeLits.Nat.
While the TypeLits interface provided by GHC does allow case-analysing the values of the naturals (GHC.TypeLits.natVal), it does not facilitate writing type-safe programs involving that AP, if one were to write:
case natVal (x :: Proxy n) of 0 -> foo x
In the RHS of this pattern match
n
is equal to0
but this isn't something GHC can reason about, as this is an ordinary pattern match on an Integer. If the type offoo
wasProxy 0 -> ...
this wouldn't typecheck and one would have to resort tounsafeCoerce
. In order to make GHC infer something like this,natVal
needs to return a GADT that includes proofs about the natural number it refers to, such that when pattern matching on that GADT the proofs become available to the typechecker.This package provides a handful of variants of such GADTs for overcoming this type of issue, as well as functions to do typesafe induction on naturals without resorting to manual GADT unpacking. The most basic form of induction - Peano-style induction (P(0) and P(n) implies P(n + 1)) can be inefficient in practice on large numbers, so this package also provides more efficient binary and arbitrary-base induction schemes.
- Author
- mniip
- Bug reports
- n/a
- Category
- Data
- Copyright
- n/a
- Homepage
- https://github.com/mniip/singleton-typelits
- Maintainer
- mniip@mniip.com
- Package URL
- n/a
- Stability
- n/a