▼Unstable: May Change Without Warning
On this page:
wrap-expr/ c
Version: 5.1.3
  top← prev  up  next → 

5 Contracts for macro subexpressions

Ryan Culpepper <ryanc@racket-lang.org>

This library provides a procedure wrap-expr/c for applying contracts to macro subexpressions.

 (require unstable/wrapc)

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

(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)
Returns a syntax object representing an expression that applies the contract represented by contract-expr to the value produced by expr.

The other arguments have the same meaning as for expr/c.

Examples:

> (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: self-contract

violation, expected <parameter?>, given: 'whoops

  contract from top-level, blaming top-level

  contract: parameter?

        at: eval:4.0

> (module mod racket
    (require (for-syntax unstable/wrapc))
    (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

  contract from top-level, blaming (quote mod)

  contract: (-> number? number?)

        at: eval:8.0

> (app (lambda (x) 'pear) 5)

the function argument of app: self-contract violation,

expected <number?>, given: 'pear

  contract from top-level, blaming top-level

  contract: (-> number? number?)

        at: eval:9.0

  top← prev  up  next →