Adding uncontentious methods from RFC FS-1004

[wallymathieu]

https://github.com/fsharp/FSharpLangDesign/blob/master/RFCs/FS-1004-result-type.md

bind : ('T -> Result<'U, 'TError>) -> Result<'T, 'TError> -> Result<'U, 'TError>
map : ('T -> 'U) -> Result<'T, 'TError> -> Result<'U, 'TError>
mapError : ('TError -> 'U) -> Result<'T, 'TError> -> Result<'T, 'U>

The implementation is heavily inspired by how the Option module is structured.

I've added the files in the collections meta folder, since that's where option.fsi and option.fs live (in my mind is somewhat similar).

[msftclas]

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[dsyme]

This looks good, I'm ok with this addition to the RFC for this release.

Please add 3-4 unit tests to the FSharp.Core unittests?

[dsyme]

AppVeyor lists this failure

[00:33:41] 1) Failed : FSharp-Tests-Core+Members+Incremental.incremental(FSI_FILE)
[00:33:41] Error running command 'C:\projects\visualfsharp-3dtit\tests\..\release\net40\bin\fsiAnyCPU.exe' with args ' -r:System.Core.dll --nowarn:20 --define:INTERACTIVE --maxerrors:1 --abortonerror test.fsx' in directory 'C:\projects\visualfsharp-3dtit\tests\fsharp\core\members\incremental'. ERRORLEVEL -1073740771 ERRORLEVEL -1073740771
[00:33:41] at NUnitConf.checkTestResult(Result`2 result) in C:\projects\visualfsharp-3dtit\tests\fsharp\nunitConf.fs:line 14

Not sure why, it looks unrelated to your changes.

[wallymathieu]

Quite odd indeed.

[wallymathieu]

That build looks a bit flaky.

[wallymathieu]

Looks like all it needed was some random nudge. ;)

[dsyme]

These summaries should be English-language. I know they're using the style from the "Option" summaries, but those ones should really be changed too :)

The MSDN docs use summary strings like Transforms an option value by using a specified mapping function.

[dsyme]

Merging, will update the doc strings separately.

[cartermp]

👍