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truth/ c
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Version: 5.2.1

4 Contracts

This library is unstable; compatibility will not be maintained. See Unstable: May Change Without Warning for more information.

 (require unstable/contract)

(non-empty-string? x)  boolean?
  x : any/c
Returns #t if x is a string and is not empty; returns #f otherwise.

Equivalent to (between/c 1 65535).

Equivalent to (between/c 0 65535).

Equivalent to (or/c path-string? (symbols 'up 'same)).

The subsequent bindings were added by Ryan Culpepper.

(if/c predicate then-contract else-contract)  contract?
  predicate : (-> any/c any/c)
  then-contract : contract?
  else-contract : contract?
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:

(or/c (-> any) any/c) ; wrong!

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).

(rename-contract contract name)  contract?
  contract : contract?
  name : 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.

(option/c contract)  contract?
  contract : contract?
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 Scheme 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.

(sequence/c elem/c ...)  contract?
  elem/c : contract?
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?.


> (define/contract predicates
    (sequence/c (-> any/c boolean?))
    (in-list (list integer?
> (for ([P predicates])
    (printf "~s\n" (P "cat")))


predicates: self-contract violation, expected: boolean?,

given: 'cat

  contract from: (definition predicates), blaming:

(definition predicates)


    (sequence/c (-> any/c boolean?))

  at: eval:2.0

> (define/contract numbers&strings
    (sequence/c number? string?)
    (in-dict (list (cons 1 "one")
                   (cons 2 "two")
                   (cons 3 'three))))
> (for ([(N S) numbers&strings])
    (printf "~s: ~a\n" N S))

1: one

2: two

numbers&strings: self-contract violation, expected:

string?, given: 'three

  contract from: (definition numbers&strings), blaming:

(definition numbers&strings)

  contract: (sequence/c number? string?)

        at: eval:4.0