| Copyright | (c) 2015, Peter Trško |
|---|---|
| License | BSD3 |
| Maintainer | peter.trsko@gmail.com |
| Stability | experimental |
| Portability | NoImplicitPrelude |
| Safe Haskell | Safe |
| Language | Haskell98 |
Data.Function.Between.Types
Description
This module defines types that behave as a precursors to types defined in lens library.
Since version 0.11.0.0.
- type PreIso r s t a b = ((b -> t) -> (s -> a) -> r) -> r
- type PreIso' r s a = PreIso r s s a a
- type PreLens r s t a b = ((b -> s -> t) -> (s -> a) -> r) -> r
- type PreLens' r s a = PreLens r s s a a
- type PrePrism r s t a b = ((b -> t) -> (s -> Either t a) -> r) -> r
- type PrePrism' r s a = PrePrism r s s a a
PreIso
type PreIso r s t a b = ((b -> t) -> (s -> a) -> r) -> r Source
Family of types that can construct isomorphism between types.
Since version 0.11.0.0.
PreLens
type PreLens' r s a = PreLens r s s a a Source
A simple PreLens, where we can not change the type of the information
we are focusing on. As a consequence neither the type of the container data
type can be changed.
Since version 0.11.0.0.
PrePrism
type PrePrism r s t a b = ((b -> t) -> (s -> Either t a) -> r) -> r Source
We can also get PrePrism by specializing PreIso:
PrePrismr s t a b =PreIsor s t (Eithert a) b
This fact is not surprising, since Prisms are actually a special case of isomorphism between two types.
Let's have a type s, and we want to extract specific information out of
it, but that information may not be there. Because of the fact that the type
s can be a sum type. Imagine e.g. standard Maybe data type:
Maybea =Nothing|Justa
How do we create something that can extrat that information from a sum type,
and if necessary, also reconstructs that sum type. The answer is Prism,
which is defined as an isomorphism between that type s and Either t aa is the information we want to extract and t is the rest that we
don't care about.
You may have noticed, that definition of PrePrism contains some type
variables that aren't mentioned in the above definition. The reason for this
is that, as with Lenses we may want to extract value of type a, but when
constructing new data type we may want to change the type of that value in
to b and therefore type s may not fit, which is the reason why we have
type t in there. Once again we can ilustrate this with Maybe. Lets say
that we have a value of s = , but if we change the type of Maybe aa in
to b, and try to create Maybe again, then it would have type Maybe b
= t
Since version 0.11.0.0.
type PrePrism' r s a = PrePrism r s s a a Source
A simple PrePrism, where we can not change the type of the information
we are focusing on. As a consequence neither the type of the container data
type can be changed.
If we define PrePrism' in terms of PreIso' then we have even better
ilustration of Prism concept in terms of isomorphism:
PrePrism'r s a =PreIso'r s (Eithert a)
Since version 0.11.0.0.