This page is part of the web mail archives of SRFI 87 from before July 7th, 2015. The new archives for SRFI 87 contain all messages, not just those from before July 7th, 2015.
Taylor R. Campbell wrote:
I looked, by the way, into some old mail archives, dating back to 1983, and couldn't find any discussion of the rationale for =>.
From MIT AI Memo 452 (RRS), p. 13: [quote]This COND is a superset of the MacLISP COND. [...] The extension to the MacLISP COND made in SCHEME is flagged by the atom =>. [...] In this sitation the form /f/ following the => should have as its value a function of one argument; if the predicate /p/ is non-NIL, this function is determined and invoked on the value returne dby the predicate. This is useful for the common sutation encountered in LISP:
(COND ((SETQ IT (GET X 'PROPERTY)) (HACK IT)) ...) which in SCHEME can be rendered without using a variable global to the COND: (COND ((GET X 'PROPERTY) => (LAMBDA (IT) (HACK IT))) ...) or, in this specific instance, simply as: (COND ((GET X 'PROPERTY) => HACK) ...) [end quote]Steele and Sussman also present a variant of IF called TEST that works similarly.