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Clarify the purpose of flat-contract-predicate

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The docs currently state that `flat-contract-predicate` is merely a holdover for backwards compatibility, and that flat contracts can be used directly as predicates now. This isn't correct: _some_ flat contracts can be used directly as predicates, but not all. Ordinary racket values that double as contracts such as numbers and symbols can't be used as predicates without using `flat-contract-predicate`. Additionally, this pull request directs users to `coerce-flat-contract` if they're seeking to build contract combinators that explicitly convert ordinary racket values into flat contracts.

Context: racket/scribble#293.
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Jack Firth 2021-02-11 23:36:58 -08:00 committed by Robby Findler
parent 8a914d9338
commit 6cfc7b880b
1 changed files with 7 additions and 2 deletions
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pkgs/racket-doc/scribblings/reference/contracts.scrbl
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@ -1101,8 +1101,13 @@ directly as @tech{flat contracts}. It exists today for backwards compatibility.
Extracts the predicate from a @tech{flat contract}. Extracts the predicate from a @tech{flat contract}.
This function is a holdover from before @tech{flat contracts} could be used Note that most @tech{flat contracts} can be used directly as predicates, but not all.
directly as predicates. It exists today for backwards compatibility. This function can be used to build predicates for ordinary Racket values that double
as contracts, such as numbers and symbols. When building a @tech{contract combinator}
that needs to explicitly convert ordinary racket values to flat contracts, consider
using @racket[coerce-flat-contract] instead of @racket[flat-contract-predicate] so
that the combinator can raise errors that use the combinator's name in the error
message.
} }
@defproc[(property/c [accessor (-> any/c any/c)] @defproc[(property/c [accessor (-> any/c any/c)]