On this page:
make-proj-contract
raise-contract-error
contract-proc

8.11 Legacy Contracts

procedure

(make-proj-contract name proj first-order)  contract?

  name : any/c
  proj : 
(or/c (-> any/c
          any/c
          (list/c any/c any/c)
          contact?
          (-> any/c any/c))
      (-> any/c
          any/c
          (list/c any/c any/c)
          contact?
          boolean?
          (-> any/c any/c)))
  first-order : (-> any/c boolean?)
Builds a contract using an old interface.

Modulo errors, it is equivalent to:
(make-contract
 #:name name
 #:first-order first-order
 #:projection
 (cond
   [(procedure-arity-includes? proj 5)
    (lambda (blame)
      (proj (blame-positive blame)
            (blame-negative blame)
            (list (blame-source blame) (blame-value blame))
            (blame-contract blame)
            (not (blame-swapped? blame))))]
   [(procedure-arity-includes? proj 4)
    (lambda (blame)
      (proj (blame-positive blame)
            (blame-negative blame)
            (list (blame-source blame) (blame-value blame))
            (blame-contract blame)))]))

procedure

(raise-contract-error val    
  src    
  pos    
  name    
  fmt    
  arg ...)  any/c
  val : any/c
  src : any/c
  pos : any/c
  name : any/c
  fmt : string?
  arg : any/c
Calls raise-blame-error after building a blame struct from the val, src, pos, and name arguments. The fmt string and following arguments are passed to format and used as the string in the error message.

procedure

(contract-proc c)

  
(->* (symbol? symbol? (or/c syntax? (list/c any/c any/c)))
     (boolean?)
     (-> any/c any))
  c : contract?
Constructs an old-style projection from a contract.

The resulting function accepts the information that is in a blame struct and returns a projection function that checks the contract.