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

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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
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17
collects/scribblings/reference/contracts.scrbl
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@ -537,9 +537,22 @@ contract describes the mandatory arguments, and is similar to the
argument description of a @racket[->] contract. The second clause argument description of a @racket[->] contract. The second clause
describes the optional arguments. The range of description can either describes the optional arguments. The range of description can either
be @racket[any] or a sequence of contracts, indicating that the 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 @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, expressions are checked as the function is called and returns,
respectively, and allow checking of the environment without an respectively, and allow checking of the environment without an
explicit connection to an argument (or a result). explicit connection to an argument (or a result).