procedure (function/c) → contract?

(function/c source/c target/c) → contract?

source/c : contract?

target/c : contract?

> (define/contract (list-length lst)     (function/c list? natural-number/c)     (if (empty? lst)       0       (add1 (list-length (rest lst)))))

> (list-length '(h e l l o))

5

> (list-length "hello")

list-length: contract violation

expected: list?

given: "hello"

in: the 1st argument of

(-> (listof any/c) natural-number/c)

contract from: (function list-length)

blaming: program

(assuming the contract is correct)

at: eval:1.0

procedure (self-map/c type/c) → contract?

type/c : contract?

> (define/contract (double n)     (self-map/c natural-number/c)     (* n 2))

> (double 5)

10

> (double "hello")

double: contract violation

expected: natural-number/c

given: "hello"

in: the 1st argument of

(-> natural-number/c natural-number/c)

contract from: (function double)

blaming: program

(assuming the contract is correct)

at: eval:4.0

procedure (thunk/c [target/c]) → contract?

target/c : contract? = any/c

> (define/contract (hello-button)     (thunk/c string?)     "hello!")

> (hello-button)

"hello!"

> (hello-button "friend")

hello-button: arity mismatch;

the expected number of arguments does not match the given

number

expected: 0

given: 1

arguments...:

"friend"

> (define/contract (hello-button)     (thunk/c number?)     "hello!")

> (hello-button)

hello-button: broke its own contract

promised: number?

produced: "hello!"

in: the range of

(-> number?)

contract from: (function hello-button)

blaming: (function hello-button)

(assuming the contract is correct)

at: eval:10.0