Gergely Buday wrote:
I wanted to express that an argument is show-able by a proper t ->
string function. It seems that I had success with the function show_
but not with the main function. Why does this simple code leads to a
too difficult unification problem?
- Gergely
$ cat bar.ur
fun show_ [t] (arg : show t) =
return<xml>{[arg]}</xml>
Something is already strange with this definition, so I suggest fixing
that first and seeing if the problem recurs. The code above tries to
show the witness of membership in the type class [show]. What you want
instead is to use that witness to render a particular value of type
[t]. You probably meant this:
fun show_ [t] (_ : show t) (arg : t) =
return <xml>{[arg]}</xml>
BTW, this function is already in the standard library and is present in
the default context, with the name [txt], with a more general type.
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