[plt-scheme] instanceof equivalent in Typed Scheme?

From: Sam TH (samth at ccs.neu.edu)
Date: Tue Jun 9 15:29:47 EDT 2009

On Tue, Jun 9, 2009 at 2:59 PM, Todd O'Bryan<toddobryan at gmail.com> wrote:
> Is there a way to check whether something is of a particular type?

First-order values such as numbers come with predicates built-in, such
as `number?'.  Structs define their own predicate.

For more complicated types, you can write functions with types like this:

> (: Type? : Any -> Boolean : Type)

for some types, but not all types, both because some such predicates
are not computable, as Matthias points out, and some cannot be
verified by Typed Scheme.

There isn't a general mechanism for defining such predicates.

sam th
samth at ccs.neu.edu

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