In the assertFoo/isFoo/checkFoo pattern, checkFoo has a check
parameter of type Checker. assertFoo calls checkFoo passes
assertChecker as the check argument. isFoo passes identChecker
as the check argument. identChecker acts precisely like an
identity function, but is typed as a Checker to indicate its
intended use.
In the
assertFoo/isFoo/checkFoopattern,checkFoohas acheckparameter of typeChecker.assertFoocallscheckFoopassesassertCheckeras thecheckargument.isFoopassesidentCheckeras thecheckargument.identCheckeracts precisely like an identity function, but is typed as aCheckerto indicate its intended use.