Search code examples
smlml

In Standard ML, how can you catch an exception like "Error: unbound variable or constructor: foo"?

I have this newbie question: in Standard ML, how can you catch an exception like "Error: unbound variable or constructor: foo"?

I tried to do this with the following program:

(foo())
handle Error msg => ();

But REPL complains: "Error: non-constructor applied to argument in pattern: Error"

Thanks in advance.

Solution

  • First of all it's handle Error => ... (or handle error => ... or handle TheSpecificExceptionIWantToCatch => ...), not handle Error msg => .... You can only write handle Foo msg => ... if Foo is a constructor with one argument, which, as the error message suggests, Error is not.

    Secondly "unbound variable" is a compilation error, not an exception, so it can't be caught.