- (alist-update! KEY VALUE ALIST [TEST]) procedure
If the list ALIST contains a pair of the form (KEY . X), then this procedure replaces X with VALUE and returns ALIST. If ALIST contains no such item, then alist-update! returns ((KEY . VALUE) . ALIST). The optional argument TEST specifies the comparison procedure to search a matching pair in ALIST and defaults to eqv?.