suzanne.soy/racket
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

clarify the role of the #:rest portion of the contract

Browse Source 
closes PR 12244
This commit is contained in:
Robby Findler 2011-10-01 15:55:58 -05:00
parent 79fbc970aa
commit 533b898277
1 changed files with 15 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
collects/scribblings/reference/contracts.scrbl
View File

@ -537,9 +537,22 @@ contract describes the mandatory arguments, and is similar to the
argument description of a @racket[->] contract. The second clause
describes the optional arguments. The range of description can either
be @racket[any] or a sequence of contracts, indicating that the
function must return multiple values. If present, the
function must return multiple values.
If present, the
@racket[rest-expr] contract governs the arguments in the rest
parameter. The @racket[pre-cond-expr] and @racket[post-cond-expr]
parameter. Note that the @racket[rest-expr] contract governs only
the arguments in the rest parameter, not those in mandatory arguments.
For example, this contract:
@racketblock[(->* () #:rest (cons/c integer? (listof integer?)) any)]
does not match the function
@racketblock[(λ (x . rest) x)]
because the contract insists that the function accept zero arguments
(because there are no mandatory arguments listed in the contract). The
@racket[->i] contract does not know that the contract on the rest argument is
going to end up disallowing empty argument lists.
The @racket[pre-cond-expr] and @racket[post-cond-expr]
expressions are checked as the function is called and returns,
respectively, and allow checking of the environment without an
explicit connection to an argument (or a result).