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doc: explain blame object passed to late-neg

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The blame object passed to a late-neg-proj function will be missing
 one party. The missing party is sometimes the negative party and
 sometimes the positive party.
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Ben Greenman 2017-05-01 18:26:01 -04:00 committed by GitHub
parent a666f1b0c1
commit 11484b9d34
1 changed files with 10 additions and 10 deletions
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pkgs/racket-doc/scribblings/reference/contracts.scrbl
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@ -2185,14 +2185,14 @@ the value of @racket[(contract-first-order-okay-to-give-up?)] (see it's document
for more explanation).
The @racket[late-neg-proj] argument defines the behavior of applying
the contract via a @deftech{late neg projection}. If it is
supplied, it accepts a @tech{blame object} that does not have a value for
the @racket[blame-negative] field. Then it must return a function that accepts
both the value that is getting the contract and the name of the blame party, in
that order. The result must either be the value (perhaps suitably wrapped
with a @tech{chaperone} or @tech{impersonator} to enforce the contract), or
signal a contract violation using @racket[raise-blame-error]. The default is
@racket[#f].
the contract via a @deftech{late neg projection}. If it is supplied, this
argument accepts a @tech{blame object} that is missing one party (see also
@racket[blame-missing-party?]). Then it must return a function that accepts
both the value that is getting the contract and the name of the missing blame
party, in that order. The result must either be the value (perhaps suitably
wrapped with a @tech{chaperone} or @tech{impersonator} to enforce the
contract), or signal a contract violation using @racket[raise-blame-error].
The default is @racket[#f].
The projection @racket[proj] and @racket[val-first-proj] are older mechanisms for
defining the behavior of applying the contract. The @racket[proj] argument
@ -2366,7 +2366,7 @@ recognized automatically and do not require this form.
If your combinator's projections operate on complete @tech{blame objects} (i.e., no
missing blame parties), the @tech{blame object} should be the first argument to this
form. Otherwise (e.g., in the case of @racket[_late-neg] projections), a pair
of the @tech{blame object} and the negative party should be used instead.
of the @tech{blame object} and the missing party should be used instead.
@history[#:added "6.4.0.4"]
}
@ -3085,7 +3085,7 @@ Produces the name used to describe the contract in error messages.
the contract checking, mostly used to create a meaningful error message if
a contract violation is detected. The resulting function's first argument
is the value that should have the contract and its second argument is
a ``missing party'' from the @tech{blame object}, to be passed to @racket[raise-contract-error].
a missing party for the @tech{blame object}, to be passed to @racket[raise-contract-error].
If possible, use this function instead of @racket[contract-val-first-projection] or
@racket[contract-projection].