6.1
4 Contracts
This library is unstable;
compatibility will not be maintained.
See Unstable: May Change Without Warning
for more information.
Returns #t if x is a string and is not empty;
returns #f otherwise.
The subsequent bindings were added by Ryan Culpepper.
Produces a contract that, when applied to a value, first tests the
value with predicate; if predicate returns true, the
then-contract is applied; otherwise, the
else-contract is applied. The resulting contract is a flat
contract if both then-contract and else-contract are
flat contracts.
For example, the following contract enforces that if a value is a
procedure, it is a thunk; otherwise it can be any (non-procedure)
value:
Note that the following contract is not equivalent:
The last contract is the same as
any/c because
or/c tries flat contracts before higher-order contracts.
A contract that describes the failure result arguments of procedures
such as
hash-ref.
Equivalent to (if/c procedure? (-> any) any/c).
Produces a contract that acts like contract but with the name
name.
The resulting contract is a flat contract if contract is a
flat contract.
The subsequent bindings were added by Asumu Takikawa.
Creates a contract that acts like contract but will also
accept #f. Intended to describe situations where a failure
or default value may be used.
The subsequent bindings were added by Carl Eastlund <cce@racket-lang.org>.
This contract recognizes Racket truth values, i.e., any value, but with a more
informative name and description. Use it in negative positions for arguments
that accept arbitrary truth values that may not be booleans.
Wraps a
sequence,
obligating it to produce as many values as there are
elem/c contracts,
and obligating each value to satisfy the corresponding
elem/c. The
result is not guaranteed to be the same kind of sequence as the original value;
for instance, a wrapped list is not guaranteed to satisfy
list?.
If min-count is a number, the stream is required to have at least that many elements in it.
Examples: |
| | | > (for ([P predicates]) | | (printf "~s\n" (P "cat"))) |
| #f | predicates: broke its contract | promised: boolean? | produced: 'cat | in: the range of | an element of | (sequence/c (-> any/c boolean?)) | contract from: (definition predicates) | blaming: (definition predicates) | at: eval:2.0 | | | | > (for ([(N S) numbers&strings]) | | (printf "~s: ~a\n" N S)) |
| | numbers&strings: broke its contract | promised: string? | produced: 'three | in: an element of | (sequence/c number? string?) | contract from: (definition numbers&strings) | blaming: (definition numbers&strings) | at: eval:4.0 | | | | 0 is x | a-sequence: broke its contract | promised: a sequence that contains at least 2 values | produced: "x" | in: (sequence/c #:min-count 2 char?) | contract from: (definition a-sequence) | blaming: (definition a-sequence) | at: eval:6.0 |
|
The subsequent bindings were added by Neil Toronto <neil.toronto@gmail.com>.
Identifies values that meet the contract elem-contract, lists of such values, lists of lists, and so on.