Implementing basic functions

[JaroslavTulach]

Pull Request Description

The language specification suggests to add five basic functions into the standard library. identity, flip, const, curry & uncurry.

Important Notes

The new functions are being added into existing Function.enso file. That may not be the best place, but it is not clear from the design spec how they are supposed to be imported. I can move them wherever needed.

There is a documentation provided for each of the functions, but I am not sure how to verify it is correct. Do we generate the documentation for stdlib somehow?

Checklist

Please include the following checklist in your PR:

• [ x ] The documentation has been updated if necessary.
• All code has been tested:
  • [ x ] Unit tests have been written where possible.

[jdunkerley]

Should make these member functions rather than extensions.

[jdunkerley]

Just the indent (4 spaces) needed to get this working as member functions.

@wdanilo - I believe we want these to be global static functions we can just call?
I don't believe this is currently possible but should be once here work, statics and import completed. Is that the case?

[jdunkerley]

These work in the current form but will need review once here. is finished.

[JaroslavTulach]

Thanks for the review @jdunkerley, I followed your advice and modified the test 3b99fc4 as suggested. Then I tried:

enso$ git merge --squash 5fca901
enso$ sbt buildEngineDistribution
enso$ ./built-distribution/enso-engine-0.0.0-dev-linux-amd64/enso-0.0.0-dev/bin/enso --run test/Tests/src/Data/Function_Spec.enso 
identity:
    - identity on number
    - identity on text
    - identity on boolean
flip:
    - flip on number
    - flip on text
const:
    - const on number
curry:
    - curry on number list
uncurry:
    - uncurry on number list

That means, once @hubertp merges his changes, the PR here shall be also mergable as it is right now.

[hubertp]

Will try to merge once my work is done