Validate a callback argument

A function stored now and called later fails at the call site, which can be a training run and several frames away from the argument that was wrong. Checking at the constructor that it is a function, and that it can take the argument it will be given, keeps the complaint next to the mistake.

Usage

check_function(f, arg, what = NULL)

Arguments

f

The user's value.

arg

Name of the argument.

what

Optional phrase naming the argument the function receives, e.g. "the number of draws". Shown in parentheses.

Value

f, invisibly.