Lists

The Basics

Believe it or not, but every list operation (more or less) can be defined in terms of these five basic operations.

null: Standard list constant. The empty list.
(cons value lst): Standard List Procedure. Create a new list by prepending value to the front of lst.
(cdr lst): Standard List Procedure. Get a list the same as lst but without the first element.
(car lst): Standard List Procedure. Get the first element of lst.
(null? lst): Standard list predicate. Checks if lst is the empty list.

Making Lists and Sublists

(list val_0 val_1 ... val_n): Standard List Procedure. Create a new list of size n+1 of the form (val_0 val_1 ... val_n).
(make-list n val): Customary List Procedure. Make a new list that consists of n copies of val.
(list-drop lst n): List Procedure. Build a new list that consists of all but the first n elements of lst.
(list-take lst n): List Procedure. Build a new list that consists of the first n elements of lst.

List Iteration Procedures

(for-each proc! lst): Standard Higher-Order List Procedure. Apply proc! to each element of the given list. Called primarily for side effects.
(map func lst): Standard Higher-Order List Procedure. Create a new list, each of whose elements is computed by applying func to the corresponding element of lst.

Additional List Procedures

Most of these are forthcoming.

(list-ref lst n): Standard List Procedure. Get the nth element of lst. Note that elements are numbered starting at 0.
(reverse lst): Standard List Procedure. Build a new list whose elements are the same as those of lst, but in the opposite order.
(member? val lst): MediaScheme List Procedure. Determine if val appears in lst. If so, returns true (#t). If not, returns false (#f).
(member val lst): Standard List Procedure. Determine if val appears in lst. If so, returns the sublist that starts with val. If not, returns false (#f).

Hybrids of `car` and `cdr`

(caar lst): Standard List Procedure. If lst's first element is a list, gets the first element of that first element, the the car of the car of lst. If lst is not a list, or its first element is not a list, reports an error.
(cadr lst): Standard List Procedure. Get the second element of lst, the car of the cdr of lst
(cddr lst): Standard List Procedure. Get all but the first two elements of lst, the cdr of the cdr of lst
(caddr lst): Standard List Procedure. Get the third element of lst, the car of the cdr of the cdr of lst.

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