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Discriminated union as a function parameter - avoiding warning messages?
f#compiler

Hi again all,

This is more an irritation than a show stopper, but can anyone tell me how to avoid the following?

I have a discriminated union type declared as :

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type RuleBody =
    | EventPattern of string*term list*string list
    | Seq of RuleBody*RuleBody*Qualifier list
    | ......

and a variety of functions declared that take parameters of one or other of the sub-types of the union such as:

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let compile_event (name, EventPattern(evname,evparms,evactions), indx : int64, symbol_table : string list) = .....

and in each case, the compiler warns about incomplete pattern matches on the function header. The calling code takes care of ensuring that each function is only invoked with the appropriate parameter type - I know that I could pass in a parameter of type RuleBody and match on type within the function, but this is a syntactic pain and, presumably, could carry a (small) performance overhead. Is there any way to tell the compiler that, hand-on-heart, I can guarantee that only an EventPattern will ever arrive here?

Thanks in advance

Martin

.

Why not change signature to

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let compile_event (name, (evname,evparms,evactions), indx : int64, symbol_table : string list) = .....

and change the callsite (presumably the callsite already is capable of matching out the carried case-data, since it knows the case hand-on-heart)?

By on 1/20/2011 10:40 AM ()

Why not change signature to

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let compile_event (name, (evname,evparms,evactions), indx : int64, symbol_table : string list) = .....

and change the callsite (presumably the callsite already is capable of matching out the carried case-data, since it knows the case hand-on-heart)?

That could work - obvious really - thanks! I'm writing (semi) realtime code and guess that passing in the Union type and matching on the actual type within the function will add an overhead that I can well do without!

Martin

By on 1/21/2011 7:47 AM ()

You are passing one of the value of discriminated union as a parameter. if you change the method signature like this you won't get compiler warning.

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let compile_even (name, rule : RuleBody, indx : int64, symbol_table : string list) = .....

Regards,

Nyi Nyi

By on 1/20/2011 8:26 AM ()

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