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create types programmatically
f#

hi there!

i am building f# expressions programmatically.
i managed to create expressions (=quotations) in a generic way with Expr.Let and Expr.Application.
i also managed to create symbols with Var(name, type) which are used in Expr.Let...

at a certain point i want to create a binding like this:

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(a, b, c) = 
foo x y z

so i tested fsi first:

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let foo a b = a+b, a*b, a/b, a%b
let barexpr = <@ let (barx, bary, barz, _) = foo 3 5 in ()@>;;

fsi says:

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Let (patternInput,
     Call (None,
           System.Tuple`4[System.Int32,System.Int32,System.Int32,System.Int32] foo(Int32, Int32),
           [Value (3), Value (5)]),
     Let (barz, TupleGet (patternInput, 2),
          Let (bary, TupleGet (patternInput, 1),
               Let (barx, TupleGet (patternInput, 0), Value (<null>)))))

so i tried to do it that way programmatically (to be able to have any number of tuple arguments...):

*1:* bind the tuple to a symbol

*2:* get elements with Expr.TupleGet

but i fail when i try to bind a tuple to a var (like patternInput) like fsi does above;
and this is just because i don't know the type of the tuple.
well, i know the elements types, but how can i programmatically construct a tuple type with these element types?

thanks for your help,
Sebastian

.

I'm not clear on exactly what you're asking; if you want to get a Type instance for System.Tuple`4[System.Int32,System.Int32,System.Int32,System.Int32], then the easiest way is:

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typeof<int*int*int*int>

If you know the tuple's size and have Type instances at runtime and want to create a tuple from that, you can do

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typedefof<_*_*_*_>.MakeGenericType(types)

If you don't know the number of elements or the types until runtime, you can do

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Microsoft.FSharp.Reflection.FSharpType.MakeTupleType(types)

Does that answer your question?

By on 4/7/2010 3:53 PM ()

yes, thank you!

however, and i just noticed that there is also another way to do it:
the left hand expression must have the same type as right hand expression (of a let), so i can just fetch it over Expr.Type...
So now i am free to switch between

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Microsoft.FSharp.Reflection.FSharpType.MakeTupleType(types)

and 

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Expr.Type

depending on what performs better...

thanks again

By on 4/8/2010 4:02 PM ()

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