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Initial work on documenting the new form and changing the documentation

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for define/contract appropriately.

svn: r11681
This commit is contained in:
Stevie Strickland 2008-09-12 15:20:02 +00:00
parent a44810f4f5
commit c32c61ab74
1 changed files with 26 additions and 12 deletions
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38
collects/scribblings/reference/contracts.scrbl
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@ -641,23 +641,37 @@ contract on the fields that the sub-struct shares with its parent are
only used in the contract for the sub-struct's maker, and the selector
or mutators for the super-struct are not provided.}
@defform[(define/contract id contract-expr init-value-expr)]{
@defform/subs[
(with-contract blame-id (wc-exports) body ...+)
([wc-exports
id
(id contract-expr)])]{
Generates a local contract boundary. The @scheme[contract-expr]
form cannot appear in expression position. The @scheme[body] of the
form allows definition/expression interleaving like a @scheme[module]
body. Names bound within the @scheme[body] must be exported to be
accessible from outside the @scheme[with-contract] form. Such
@scheme[id]s can either be paired with a @scheme[contract-expr] or
exported without a contract.
Attaches the contract @scheme[contract-expr] to
@scheme[init-value-expr] and binds that to @scheme[id].
The @scheme[blame-id] is used for the positive positions of
contracts paired with exported @scheme[id]s. Contracts broken
within the @scheme[with-contract] @scheme[body] will use the
@scheme[blame-id] for their negative position.
@defform*[(define/contract id contract-expr init-value-expr)
(define/contract (head args) contract-expr body ...+]{
Works like @scheme[define], except that the contract
@scheme[contract-expr] is attached to the bound value.
The @scheme[define/contract] form treats individual definitions as
units of blame. The definition itself is responsible for positive
(co-variant) positions of the contract and each reference to
@scheme[id] (including those in the initial value expression) must
meet the negative positions of the contract.
Error messages with @scheme[define/contract] are not as clear as those
provided by @scheme[provide/contract], because
@scheme[define/contract] cannot detect the name of the definition
where the reference to the defined variable occurs. Instead, it uses
the source location of the reference to the variable as the name of
that definition.}
@scheme[id] outside of the definition must meet the negative positions
of the contract. It is equivalent to wrapping a single @scheme[define]
with a @scheme[with-contract] form that pairs the @scheme[contract-expr]
with the bound identifier.}
@defform*[[(contract contract-expr to-protect-expr
positive-blame-expr negative-blame-expr)