Christopher Atkins

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    5 comments  ·  F# Language  ·  Flag idea as inappropriate…  ·  Admin →

    This proposal is “approved in principle” for F# 4.0+. It would make a good addition to F#. (I don’t think the loss of purity (e.g. wr.t. ordering of union cases) is a critical problem and I believe you can turn of the DefaultAugmentation in any case)

    Some technical issues may need to be ironed out during implementation.

    If this is done, the Tag properties present on these types should also be revealed, that is covered by a separate item.

    An implementation and testing would need to be provided by someone in the F# community (possibly including Microsoft or Microsoft Research, though not limited to them).

    Implementations of approved language design can now be submitted as pull requests to the appropriate branch of See for information on contributing to the F# language and core library..

    I’d be glad to help guide people through the implementation process.

    If you…

    Christopher Atkins commented  · 

    There are a few considerations to take into account when tackling this, per Don Syme:

    * The problem is that the generated “Is*” and “New*” for unions are inserted very late in the compilation pipeline, in the “ILX” phase, using nasty code that is somewhat ancient. There are lots of corresponding cases in tc.fs and check.fs to check that the user doesn’t define these him/herself.

    * The whole generation of these should probably be lifted up to happen during type checking (the same time we generate compare/equality methods, for example, see augment.fs). Then the “check for duplicates” core would be irrelevant.

    * The messiness is compounded by the fact that there are special cases in ILX generation for lists, options and AllowNullValueAsRepresentation unions.

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