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non-empty-string?
port-number?
tcp-listen-port?
path-piece?
if/  c
failure-result/  c
rename-contract
maybe/  c
truth/  c
treeof
6.2.1
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4 Contracts

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

 (require unstable/contract)
  package: unstable-contract-lib

procedure

(non-empty-string? x) → boolean?

  x : any/c
Returns #t if x is a string and is not empty; returns #f otherwise.

value

port-number? : contract?

Equivalent to (between/c 1 65535).

value

tcp-listen-port? : contract?

Equivalent to (between/c 0 65535).

value

path-piece? : contract?

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

The subsequent bindings were added by Ryan Culpepper.

procedure

(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:

(if/c procedure? (-> any) any/c)

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.

value

failure-result/c : contract?

A contract that describes the failure result arguments of procedures such as hash-ref.

Equivalent to (if/c procedure? (-> any) any/c).

procedure

(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.

procedure

(maybe/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>.

value

truth/c : flat-contract?

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.

The subsequent bindings were added by Neil Toronto <neil.toronto@gmail.com>.

procedure

(treeof elem-contract) → contract?

  elem-contract : contract?
Identifies values that meet the contract elem-contract, lists of such values, lists of lists, and so on.

Examples:

> (define number-tree/c (treeof number?))
> (flat-contract? number-tree/c)

#t

> (define number-tree? (flat-contract-predicate number-tree/c))
> (number-tree? 4)

#t

> (number-tree? '(4 5))

#t

> (number-tree? '((4 5) 6))

#t

> (number-tree? '(4 . 5))

#f

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