7.6 Contract Utilities
Returns #t if its argument is a contract (i.e., constructed
with one of the combinators described in this section or a value that
can be used as a contract) and #f otherwise.
Returns
#t if its argument is a contract that guarantees that
it returns a value which passes
chaperone-of? when compared to
the original, uncontracted value.
Returns #t when its argument is a contract that can be
checked immediately (unlike, say, a function contract).
For example,
flat-contract constructs flat contracts from predicates, and
symbols, booleans, numbers, and other ordinary Racket values
(that are defined as contracts) are also
flat contracts.
Extracts the predicate from a flat contract.
Returns the contract attached to v, if recorded.
Otherwise it returns #f.
Returns #t if v is a value that
has a recorded contract attached to it.
Returns #t if the contract x accepts either fewer
or the same number of values as y does.
This function is conservative, so it may return #f when
x does, in fact, accept fewer values.
Returns a boolean indicating whether the first-order tests
of contract pass for v.
If it returns #f, the contract is guaranteed not to
hold for that value; if it returns #t, the contract
may or may not hold. If the contract is a first-order
contract, a result of #t guarantees that the
contract holds.
Produces the name used to describe the contract in error messages.
Produces the first-order test used by
or/c to match values to
higher-order contracts.
Produces the projection defining a contract’s behavior on protected values.
Makes a contract that accepts no values, and reports the
name sexp-name when signaling a contract violation.
A parameter that is used when constructing a
contract violation error. Its value is procedure that
accepts three arguments:
the blame object for the violation,
the value that the contract applies to, and
a message indicating the kind of violation.
The procedure then
returns a string that is put into the contract error
message. Note that the value is often already included in
the message that indicates the violation.
Examples: |
| | > (current-blame-format show-blame-error) | | | > (f 2) | 1 | | > (f 1) | Contract Violation! | Guilty Party: (function f) | Innocent Party: top-level | Contracted Value Name: f | Contract Location: #(struct:srcloc eval 4 0 4 1) | Contract Name: (-> integer? integer?) | Offending Value: 1/2 | Offense: expected <integer?>, given: 1/2 | | > (f 1/2) | Contract Violation! | Guilty Party: top-level | Innocent Party: (function f) | Contracted Value Name: f | Contract Location: #(struct:srcloc eval 4 0 4 1) | Contract Name: (-> integer? integer?) | Offending Value: 1/2 | Offense: expected <integer?>, given: 1/2 |
|
Delays the evaluation of its argument until the contract is checked,
making recursive contracts possible. If type is given, it
describes the expected type of contract and must be one of the keywords
#:impersonator, #:chaperone, or #:flat. If
type is not given, an impersonator contract is created.
This optimizes its argument contract expression by
traversing its syntax and, for known contract combinators,
fuses them into a single contract combinator that avoids as
much allocation overhead as possible. The result is a
contract that should behave identically to its argument,
except faster (due to less allocation).
This defines a recursive contract and simultaneously
optimizes it. Semantically, it behaves just as if
the
-opt/c were not present, defining a function on
contracts (except that the body expression must return a
contract). But, it also optimizes that contract definition,
avoiding extra allocation, much like
opt/c does.
For example,
defines the bst/c contract that checks the binary
search tree invariant. Removing the -opt/c also
makes a binary search tree contract, but one that is
(approximately) 20 times slower.