Gergely Buday wrote:
my idea is to write a function that projectds records to a given set
of names. Is it doable in Ur/Web?
I'm not sure exactly what you're asking for. Does the [---] operator do the
trick? Its first argument is a value of record type, and its second
argument is a constructor of kind [{Type}], specifying which fields to
remove from the record.
It is clear what is record.1 . I would like to have
record.[1,2,3,4]
independently what other fields does r have.
Perhaps I wasn't clear enough about what I was suggesting. Consider
this function that wraps the built-in [---] operator:
(* *)
fun projection [fs1 ::: {Type}] [fs2 ::: {Type}] [fs1 ~ fs2] (r : $(fs1
++ fs2)) : $fs2 = r --- _
(* *)
Here is a simple example of using it:
(* *)
type r1 = {A : int, B : float, C : string}
type r2 = {A : int, C : string}
val r1 : r1 = {A = 1, B = 2.0, C = "x"}
val r2 : r2 = projection r1
(* *)
Is that what you're looking to do? If so, you can cut out the named
function and simply write [r1 --- _] in the last line (and in other
related contexts).
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