I think this is an interpreter bug, that it automatically coerces a Union
type Union(xx, "yy") to its subtype "yy". (Interpreter can handle types like
Union(Integer,String) )
You can use the following workaround:
remove(x+->x case "failed", l)
But the result type is still List(Union(IntegerMod(10),"failed")).
Another way is to use filter when creating the list:
T ==> IntegerMod 10
[y::T for i in 0..9 | (y := recip(i::T)) case T]
BTW, I think the "Maybe" approach doesn't have this problem.
It can enable functional ways to solve this problem, for example
in Haskell, it only uses ">>= maybeToList":
Prelude> import Data.Maybe
Prelude Data.Maybe> let l = [Nothing, Just 1, Nothing, Just 7]
l :: Num a => [Maybe a]
Prelude Data.Maybe> l >>= maybeToList
[1,7]
it :: Num b => [b]
On Sat, May 26, 2018 at 7:42 PM, Prof. Dr. Johannes Grabmeier privat
<[email protected]> wrote:
> What is going wrong here:
>
> (1) -> li := [2,4,3,2,5,2,7,2,2,7]
>
> (1) [2, 4, 3, 2, 5, 2, 7, 2, 2, 7]
>
> Type: List(PositiveInteger)
> (2) -> remove(2,li)
>
> (2) [4, 3, 5, 7, 7]
>
> Type: List(PositiveInteger)
> (3) -> li10 := [recip(i::IntegerMod 10) for i in 0..9]
>
> (3) ["failed", 1, "failed", 7, "failed", "failed", "failed", 3,
> "failed", 9]
> Type:
> List(Union(IntegerMod(10),"failed"))
> (4) -> f : Union(IntegerMod(10),"failed") := "failed"
>
> (4) "failed"
>
> Type: Union("failed",...)
> (5) -> remove(f, li10)
> There are 3 exposed and 1 unexposed library operations named remove
> having 2 argument(s)
> but none was determined to be applicable. Use HyperDoc Browse, or
> issue
> )display op remove
> to learn more about the available operations. Perhaps
> package-calling the operation or
> using coercions on the arguments will allow you to apply the
> operation.
>
> Cannot find a definition or applicable library operation named remove
> with argument type(s)
>
> failed
> List(Union(IntegerMod(10),"failed"))
>
> Perhaps you should use "@" to indicate the required return type,
> or "$" to specify which
> version of the function you need
>
> --
> Mit freundlichen Grüßen
>
> Johannes Grabmeier
>
> Prof. Dr. Johannes Grabmeier
> Köckstraße 1, D-94469 Deggendorf
> Tel. +49-(0)-991-2979584, Tel. +49-(0)-151-681-70756
> Tel. +49-(0)-991-3615-141 (d), Fax: +49-(0)-32224-192688
>
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