12 mzlib/contract

▼ |  | Mz Lib: Legacy Libraries

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2 | mzlib/ a-unit
3 | mzlib/ async-channel
4 | mzlib/ awk
5 | mzlib/ class
6 | mzlib/ cm
7 | mzlib/ cm-accomplice
8 | mzlib/ cmdline
9 | mzlib/ cml
10 | mzlib/ compat
11 | mzlib/ compile
12 | mzlib/ contract
13 | mzlib/ control
14 | mzlib/ date
15 | mzlib/ deflate
16 | mzlib/ defmacro
17 | mzlib/ etc
18 | mzlib/ file
19 | mzlib/ for
20 | mzlib/ foreign
21 | mzlib/ include
22 | mzlib/ inflate
23 | mzlib/ integer-set
24 | mzlib/ kw
25 | mzlib/ list
26 | mzlib/ match
27 | mzlib/ math
28 | mzlib/ md5
29 | mzlib/ os
30 | mzlib/ pconvert
31 | mzlib/ pconvert-prop
32 | mzlib/ plt-match
33 | mzlib/ port
34 | mzlib/ pregexp
35 | mzlib/ pretty
36 | mzlib/ process
37 | mzlib/ restart
38 | mzlib/ runtime-path
39 | mzlib/ sandbox
40 | mzlib/ sendevent
41 | mzlib/ serialize
42 | mzlib/ shared
43 | mzlib/ string
44 | mzlib/ struct
45 | mzlib/ stxparam
46 | mzlib/ surrogate
47 | mzlib/ tar
48 | mzlib/ thread
49 | mzlib/ trace
50 | mzlib/ traceld
51 | mzlib/ trait
52 | mzlib/ transcr
53 | mzlib/ unit
54 | mzlib/ unit-exptime
55 | mzlib/ unit200
56 | mzlib/ unitsig200
57 | mzlib/ zip
| Bibliography
| Index

On this page:

define/ contract
box/ c
vectorof
vector/ c
struct/ c
build-flat-contract
->
->*
opt->
opt->*
->d
->d*
->r
->pp
->pp-rest
case->
object-contract

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(require mzlib/contract) | package: compatibility-lib

> NOTE: This library is deprecated; use racket/contract, instead. This library is designed as a backwards compatible library for old uses of contracts. It should not be used for new libraries.

The main differences: the function contract syntax is more regular and function contracts now support keywords, and union is now or/c.

The mzlib/contract library re-exports many bindings from racket/contract:

| </c |  | flat-rec-contract
| <=/c |  | guilty-party
| =/c |  | integer-in
| >/c |  | list/c
| >=/c |  | listof
| and/c |  | make-none/c
| any |  | make-proj-contract
| any/c |  | natural-number/c
| between/c |  | none/c
| box-immutable/c |  | not/c
| build-compound-type-name |  | one-of/c
| coerce-contract |  | or/c
| cons/c |  | parameter/c
| contract |  | printable/c
| contract-first-order-passes? |  | promise/c
| contract-violation->string |  | provide/contract
| contract? |  | raise-contract-error
| define-contract-struct |  | real-in
| false/c |  | recursive-contract
| flat-contract |  | string/len
| flat-contract-predicate |  | symbols
| flat-contract? |  | syntax/c
| flat-murec-contract |  | vector-immutable/c
| flat-named-contract |  | vector-immutableof

It also provides the old version of the following contracts:

> syntax (define/contract id contract-expr init-value-expr)

Attaches the contract contract-expr to init-value-expr and binds that to id.

The define/contract form treats individual definitions as units of blame. The definition itself is responsible for positive (co-variant) positions of the contract and each reference to id (including those in the initial value expression) must meet the negative positions of the contract.

Error messages with define/contract are not as clear as those provided by provide/contract, because define/contract cannot detect the name of the definition where the reference to the defined variable occurs. Instead, it uses the source location of the reference to the variable as the name of that definition.

> procedure (box/c c) → flat-contract?
> c : flat-contract?

Returns a flat contract that recognizes boxes. The content of the box must match c.

> procedure (vectorof c) → flat-contract?
> c : flat-contract?

Accepts a flat contract and returns a flat contract that checks for vectors whose elements match the original contract.

> procedure (vector/c c ...) → flat-contract?
> c : flat-contract?

Accepts any number of flat contracts and returns a flat contract that recognizes vectors. The number of elements in the vector must match the number of arguments supplied to vector/c, and each element of the vector must match the corresponding flat contract.

> syntax (struct/c struct-id flat-contract-expr ...)

Produces a flat contract that recognizes instances of the structure type named by struct-id, and whose field values match the flat contracts produced by the flat-contract-exprs.

> procedure (build-flat-contract name predicate) → flat-contract?
> name : symbol?
> predicate : (-> any/c any)

Builds a flat contract out of predicate, giving it the name name. Nowadays, just using predicate directly is preferred.

> syntax (-> contract-dom-expr ... any)
> (-> contract-dom-expr ... contract-rng-expr)

This is a restricted form of racket/contract’s -> contract that does not handle keyword arguments or multiple value results.

> syntax (->* (contract-dom-expr ...) ->*rng)
> (->* (contract-dom-expr ...) contract-rest-expr ->*rng)
> ->*rng |  | = |  | (contract-rng-expr ...)
> |  | | |  | any

The ->* form matches up to racket/contract’s -> and ->*, according to the following rules; each equation on the left refers to a mzlib/contract combinator; on the right are the racket/contract equivalents.

> (->* (contract-dom-expr ...) any) =
> (-> contract-dom-expr ... any)

> (->* (contract-dom-expr ...) (contract-rng-expr ...)) =
> (-> contract-dom-expr ... (values contract-rng-expr))

> (->* (contract-expr ...) contract-rest-expr any) =
> (->* (contract-expr ...) #:rest contract-rest-expr any)

> (->* (contract-expr ...) contract-rest-expr (contract-rng-expr ...)) =
> (->* (contract-expr ...)
> #:rest contract-rest-expr
> (values contract-rng-expr ...))

> syntax (opt-> (contract-req-expr ...) (contact-opt-expr ...) any)
> (opt-> (contract-req-expr ...) (contact-opt-expr ...) contract-rng-expr)

The opt-> form is a simplified verison of racket/contract’s ->* and appearances of opt-> can be simply replaced with ->*.

> syntax (opt->* (contract-req-expr ...) (contact-opt-expr ...) any)
> (opt->* (contract-req-expr ...) (contact-opt-expr ...) (contract-rng-expr ...))

The opt->* form matches up to racket/contract’s ->*, according to the following rules; each equation on the left refers to a mzlib/contract combinator; on the right are the racket/contract equivalents.

> (opt->* (contract-req-expr ...) (contract-opt-expr ...) any) =
> (->* (contract-req-expr ...) (contract-opt-expr ...) any)

> (opt->* (contract-req-expr ...)
> (contract-opt-expr ...)
> (contract-rng-expr ...)) =
> (->* (contract-req-expr ...)
> (contract-opt-expr ...)
> (values contract-rng-expr ...))

> syntax (->d contract-dom-expr ... contract-rng-fun-expr)

The ->d contract constructor is just like ->, except that the range position is expected to be a function that accepts the actual arguments passed to the function, and returns a contract for the range. For example, this is one contract for sqrt:

> (->d real?
> (λ (in)
> (and/c real?
> (λ (out)
> (< (abs (- (sqr out) in))
> 0.01)))))

It says that the input must be a real number, and so must the result, and that the square of the result is within 0.01 of input.

> syntax (->d* (contract-dom-expr ...) contract-rng-fun-expr)
> (->d* (contract-dom-expr ...) contract-rest-expr contract-rng-fun-expr)

The ->d* contract constructor is a generalization of ->d to support multiple values and rest arguments.

In the two sub-expression case, the first sequence of contracts are contracts on the domain of the function and the second subexpression is expected to evaluate to a function that accepts as many arguments as there are expressions in the first position. It should return multiple values: one contract for each result of the function.

In the three sub-expression case, the first and last subexpressions are just like the sub-expressions in the two sub-expression case; the middle sub-expression si expected to evaluate to a contract on the rest argument.

> syntax (->r ([dom-x contract-dom-expr] ...) rng)
> (->r ([dom-x contract-dom-expr] ...) rest-x contract-rest-expr rng)
> rng |  | = |  | any
> |  | | |  | (values contract-expr ...)
> |  | | |  | contract-expr

The ->r form is a simplified version of racket/contract’s ->i, where each contract-dom-expr is parameterized over all of the dom-x variables (and does lax checking; see ->d for details).

> syntax (->pp ([dom-x contract-dom-expr] ...) pre-cond-expr any)
> (->pp ([dom-x contract-dom-expr] ...)
> pre-cond-expr
> (values [rng-x contract-rng-expr] ...)
> post-cond-expr)
> (->pp ([dom-x contract-dom-expr] ...)
> pre-cond-expr
> contract-rng-expr
> rng-x
> post-cond-expr)

The ->pp form, like ->r is a simplified version of racket/contract’s ->i, where each contract-dom-expr is parameterized over all of the dom-x variables (and does lax checking; see racket/contract’s ->d for details). Unlike ->r, it also has pre- and post-condition expressions; these expressions are also implicitly parameterized over all of the dom-x variables and the post-condition is also paramterized over rng-x, which is bound to the result of the function.

> syntax (->pp-rest ([dom-x contract-dom-expr] ...) rest-x rest-contract-expr pre-cond-expr any)
> (->pp-rest ([dom-x contract-dom-expr] ...)
> rest-x rest-contract-expr
> pre-cond-expr
> (values [rng-x contract-rng-expr] ...)
> post-cond-expr)
> (->pp-rest ([dom-x contract-dom-expr] ...)
> rest-x rest-contract-expr
> pre-cond-expr
> contract-rng-expr
> rng-x
> post-cond-expr)

Like ->pp, but with an additional contract for the rest arguments of the function.

> syntax (case-> mzlib/contract-arrow-contract-expr ...)

Builds a contract analogous to case-lambda, where each case comes from one of the contract expression arguments (tried in order).

> syntax (object-contract [id mzlib/contract-arrow-contract-expr] ...)

Builds a contract for objects where each id is expected to be a method on the object living up to the corresponding contract
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