procedure (wrap-expr/c   contract-expr             expr            [ #:positive pos-blame             #:negative neg-blame             #:name expr-name             #:macro macro-name             #:context context])   →   syntax?

contract-expr : syntax?

expr : syntax?

pos-blame   :   (or/c syntax? string? module-path-index?       'from-macro 'use-site 'unknown)       =   'use-site

neg-blame   :   (or/c syntax? string? module-path-index?       'from-macro 'use-site 'unknown)       =   'from-macro

expr-name : (or/c identifier? symbol? string? #f) = #f

macro-name : (or/c identifier? symbol? string? #f) = #f

context : (or/c syntax? #f) = (current-syntax-context)

> (define-syntax (myparameterize1 stx)     (syntax-case stx ()       [(_ ([p v]) body)        (with-syntax ([cp (wrap-expr/c                           #'parameter? #'p                           #:name "the parameter argument"                           #:context stx)])          #'(parameterize ([cp v]) body))]))

> (myparameterize1 ([current-input-port                      (open-input-string "(1 2 3)")])     (read))

'(1 2 3)

> (myparameterize1 (['whoops 'something])     'whatever)

the parameter argument of myparameterize1: broke its own

contract

promised: parameter?

produced: 'whoops

in: parameter?

contract from: top-level

blaming: top-level

(assuming the contract is correct)

at: eval:4.0

> (module mod racket     (require (for-syntax syntax/contract))     (define-syntax (app stx)       (syntax-case stx ()         [(app f arg)          (with-syntax ([cf (wrap-expr/c                             #'(-> number? number?)                             #'f                             #:name "the function argument"                             #:context stx)])            #'(cf arg))]))     (provide app))

> (require 'mod)

> (app add1 5)

6

> (app add1 'apple)

the function argument of app: contract violation

expected: number?

given: 'apple

in: the 1st argument of

(-> number? number?)

contract from: top-level

blaming: (quote mod)

(assuming the contract is correct)

at: eval:8.0

> (app (lambda (x) 'pear) 5)

the function argument of app: broke its own contract

promised: number?

produced: 'pear

in: the range of

(-> number? number?)

contract from: top-level

blaming: top-level

(assuming the contract is correct)

at: eval:9.0