Editing CTRex (section)

= Comparison with other approaches =

Here we compare with other approaches. 

== HList records ==

The [http://hackage.haskell.org/package/HList HList package] provides [http://hackage.haskell.org/package/HList-0.3.0.1/docs/Data-HList-Record.html extensible records] build on heterogeneous lists. The differences with are as follows:

* Rows are not sorted. This has the following downsides:
**  Compile time operations, such as reordering the labels and checking for   duplicate labels is costly (at compile time) [http://code.haskell.org/~aavogt/HList-benchmark/a.html link]
**  <hask>{x = 0, y = 0 }</hask> and <hask>{ y = 0, x = 0 } </hask> do not have the same type. Hence, is we give a type declaration for the first and want to put in the latter, we need to call a manual conversion function.
* Constrained row operations are less convenient, since 
** the Record newtype needs to be unwrapped, and
** there is no definition provided to create instances of [http://hackage.haskell.org/package/HList-0.3.0.1/docs/Data-HList-FakePrelude.html#t:ApplyAB applyAB] that work on <hask>LVPair l a</hask> from instances that work on just <hask>a</hask>
** however there similarities between the two
{|
! CTRex function
! HList function(s)
|-
| rinit
| [http://hackage.haskell.org/package/HList-0.3.0.1/docs/Data-HList-HList.html#g:15 hReplicate]
|-
| erase
| [http://hackage.haskell.org/package/HList-0.3.0.1/docs/Data-HList-HList.html#t:HMapOut hMapOut]
|-
| eraseZip
| [http://hackage.haskell.org/package/HList-0.3.0.1/docs/Data-HList-HZip.html hZip] with hMapOut
|}
* Currently, the run time complexity of extend, restriction and lookup is O(n), versus O(log n) for CTRex. Proposals have been done to make this faster [http://www.fing.edu.uy/~mviera/papers/pepm13.pdf paper].
* Duplicate labels are disallowed in HList.
* HList has nicer support for  [http://hackage.haskell.org/package/HList-0.3.0.1/docs/Data-HList-MakeLabels.html writing labels]

== Trex (Hugs) ==

The Haskell interpreter hugs supports a type system extension that allows extensible records. The differences are as follows:

* Constrained row operations are not available(?)
* Duplicate labels are disallowed
* Record merge not available (?)
* Can pattern match on records(?)
* Nicer syntax
* More (?)

== More ==

More to come! Please add stuff!