design question

[Raoul Duke]

hi, a scenario 

enum of n values. 

api function that takes the enum. 

but throws error for some subset of enum values. 

how could we statically be told, enforce do not call the api fn in those cases?

besides "rtfm". 

[Vanessa McHale]

You could I suppose have a polymorphic type and pass in ‘void’. I had an idea for something here: http://blog.vmchale.com/article/ann

In ATS I guess it would be

datatype Impossible

datatype A(phantom: type) = A | B | C of (phantom)

Then A(Impossible) would be sort of like a subtype of A(void) or at least you could manipulate it like that.

I’m not sure such a solution is worth it though! Might be better to just RTFM :P

Cheers,

Vanessa McHale

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[Hongwei Xi]

Currently, my practice is just declare something like:

abstype myenum = int

or

abstype myenum(i:int) = int

Then implement 'myenum' somewhere in a file. It can clearly be done, but it is really tedious,

involving a lot of boilerplate type of code. I suppose some kind of meta-programming can be

supported so as to reduce/eliminate this kind of coding.

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