Great, thanks. I clearly need to add the section on contracts to my re-read list. I thought I understood them, but apparently there are still bits that I'm missing.
On Wed, May 22, 2019 at 1:23 PM Alexis King <[email protected]> wrote: > Your intuition is right, but let me make it more precise: foo? is used > when something is a flat contract, and foo/c is used otherwise. Flat > contracts only check *first order properties* of values, which is a > technical term that captures what you mean by “general nature.” > > The important distinction is that first order properties can be checked > immediately, whereas checking of higher-order properties may need to be > delayed. For example, when you write the contract > > (-> integer? string?) > > > then you can check immediately that the value is a procedure (via the > procedure? predicate), but you have to wait until the function is called to > check that it is actually passed an integer. Therefore, non-flat contracts > add proxying wrappers to values that do the deferred checking. > > Since flat contracts only perform first-order checks, a flat contract can > be used as a predicate, so you can write (foo? x) to get back a boolean. > Likewise, all predicates can be used as flat contracts. This is why the > foo? naming scheme is used for those contracts, since foo? is the > historical naming convention in Scheme and its descendants for naming > predicates. The foo/c naming convention is newer, and is specific to > contracts, so it is used for contracts and contract combinators that are > not simple predicates, and therefore cannot use the foo? naming convention. > > Alexis > > On May 22, 2019, at 12:06, David Storrs <[email protected]> wrote: > > Is the idea that foo/c is used only when it will specify structure (e.g. > (hash/c any/c symbol?)) whereas foo? is used to check that a thing has a > general nature? > > > -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/CAE8gKodbUevOE1s1fXyrG%2BLSLpOw6K555apzQyzouFdyPibmbw%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
