Functions: functio.ss

The procedures second, third, fourth, fifth, sixth, seventh, and eighth access the corresponding element from a list.

Applies f to each element of l (from left to right) until f returns a true value for some element, in which case that element is returned. If f does not return a true value for any element of l, #f is returned.

Returns #t if bool1 and bool2 are both #t or both #f, and returns #f otherwise. If either bool1 or bool2 is not a Boolean, the exn:application:type exception is raised.

Creates a list of n elements by applying f to the integers from 0 to in order, where n is a non-negative integer. The ith element of the resulting list is (f (- i 1)).

Creates a string of length n by applying f to the integers from 0 to in order, where n is a non-negative integer and f returns a character for the n invocations. The ith character of the resulting string is (f (- i 1)).

Creates a vector of n elements by applying f to the integers from 0 to in order, where n is a non-negative integer. The ith element of the resulting vector is (f (- i 1)).

Returns a procedure that takes x and returns (call-with-values (lambda () (g x)) f).

Returns #t if v is a value created with cons, #f otherwise.

The empty list.

Returns #t if v is the empty list, #f otherwise.

Boolean false.

Applies f to each element in l (from left to right) and returns a new list that is the same as l, but omitting all the elements for which f returned #f.

Returns the first element of the list l. (The first procedure is a synonym for car.)

(foldl f init l )

Like map, foldl applies a procedure f to the elements of one or more lists. While map combines the return values into a list, foldl combines the return values in an arbitrary way that is determined by f.

If foldl is called with n lists, the f procedure takes n+1 arguments. The extra value is the combined return values so far. The f procedure is initially invoked with the first item of each list; the final argument is init. In subsequent invocations of f, the last argument is the return value from the previous invocation of f. The input lists are traversed from left to right, and the result of the whole foldl application is the result of the last application of f. (If the lists are empty, the result is init.)

For example, reverse can be defined in terms of foldl:

  (define reverse
    (lambda (l)
      (foldl cons '() l))) 

(foldr f init l )

Like foldl, but the lists are traversed from right to left.

For example, a restricted map (that works only on single-argument procedures) can be defined in terms of foldr:

  (define simple-map
    (lambda (f list)
      (foldr (lambda (v l) (cons (f v) l)) '() list))) 

Returns v.

Invokes thunk and returns the result. If an exception occurs during the application of thunk, no error is reported and void is returned. Break exceptions, however, are propagated.

Returns the last pair in list, raising an error if list is not a pair (but list does not have to be a proper list).

Repeatedly invokes the f procedure until the done? procedure returns #t. The procedure is best described by its implementation:

  (define loop-until
    (lambda (start done? next f)
      (let loop ([i start])
        (unless (done? i)
          (f i)
          (loop (next i)))))) 

Applies f to each element of l (from left to right) until f returns a true value for some element, in which case the tail of l starting with that element is returned. If f does not return a true value for any element of l, #f is returned.

Sorts list using the comparison procedure less-than?. This implementation is not stable (i.e., if two elements in the input are ``equal,'' their relative positions in the output may be reversed).

Sorts list using the comparison procedure less-than?. This implementation is not stable (i.e., if two elements in the input are ``equal,'' their relative positions in the output may be reversed).

Returns list without the first instance of item, where an instance is found by comparing item to the list items using equal?. The default value for equal? is equal?. When equal? is invoked, item is the first argument.

Like remove, except that the first argument is a list of items to remove, instead of a single item.

Calls remove with eq? as the comparison procedure.

Calls remove* with eq? as the comparison procedure.

Calls remove with eqv? as the comparison procedure.

Calls remove* with eqv? as the comparison procedure.

Returns a list that contains all but the first element of the non-empty list l. (The rest procedure is a synonym for cdr.)

Returns #t if symbol1 and symbol2 are equivalent (as determined by eq?), #f otherwise. If either symbol1 or symbol2 is not a symbol, the exn:application:type exception is raised.

Boolean true.