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 <david.sto...@gmail.com > <mailto:david.sto...@gmail.com>> 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 racket-users+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/3D2F671B-9322-43FC-B51D-2BA6542E2D67%40gmail.com. For more options, visit https://groups.google.com/d/optout.
