Internal to a useful pattern for writing checking logic
(a "checkFoo" function) that can be used to implement a predicate
(an "isFoo" function) or a validator (an "assertFoo" function).
A predicate ideally only returns true or false and rarely throws.
A validator throws an informative diagnostic when the predicate
would have returned false, and simply returns undefined normally
when the predicate would have returned true.
The internal checking function that they share is parameterized by a
Checker that determines how to proceed with a failure condition.
Predicates pass in an identity function as checker. Validators
pass in assertChecker which is a trivial wrapper around assert.
Internal to a useful pattern for writing checking logic (a "checkFoo" function) that can be used to implement a predicate (an "isFoo" function) or a validator (an "assertFoo" function).
trueorfalseand rarely throws.false, and simply returnsundefinednormally when the predicate would have returnedtrue.Checkerthat determines how to proceed with a failure condition. Predicates pass in an identity function as checker. Validators pass inassertCheckerwhich is a trivial wrapper aroundassert.See the various uses for good examples.