/ case-q /

CASE?

status:: We are not trying to persuade you to use CASE? in place of the Eaker's CASE (the CASE..OF.. structure that is now ANS Forth). But we do recommend you to know the alternative approach. Today's acceptance of CASE? is unknown.
description:: CASE? is an elegant alternative to Eaker's CASE..OF..ENDOF..ENDCASE : CASE? ( x x -- true ) ( x y -- x false ) OVER = DUP IF NIP THEN ; CASE? is what IF misses to be OF . In other words, CASE? IF is equivalent to OF (here we assume that ENDOF is a synonym of ELSE). CASE? IF is equivalent to OVER = IF DROP
original message:: From: Neil Bawd (neilbawd@earthlink.net) Subject: Re: OT Change of case Newsgroups: comp.lang.forth Message-ID: <B7D5D0B9.1F754%neilbawd@earthlink.net> Date: 2001-09-25 06:12:57 PST in 3BB0329D.F9689922@yahoo.com, Michael L.Gassanenko at m_l_g3@yahoo.com wrote: > How do you use CASE? ? As I recall, `CASE?` was introduced by Klaus Schleissiek in the early 80's for Volksforth. Pinhole optimization of `CASE? IF` should give optimized `OVER = IF DROP`. Thus Julian V. Noble's `[put_char]` could be: : [put_char] ( char -- 0..3 ) BL CASE? IF 1 EXIT THEN [char] { CASE? IF 2 EXIT THEN [char] } CASE? IF 3 EXIT THEN DROP 0 ; Or: : [put_char] ( char -- 0..3 ) BL CASE? IF 1 ELSE [char] { CASE? IF 2 ELSE [char] } CASE? IF 3 ELSE DROP 0 THEN THEN THEN ; Or with `COND ... THENS`: : [put_char] ( char -- 0..3 ) COND BL CASE? IF 1 ELSE [char] { CASE? IF 2 ELSE [char] } CASE? IF 3 ELSE DROP 0 THENS ; `CASE?` can be conjoined with other tests or further `CASE?`s. [char] A CASE? ORIF [char] a CASE? THEN IF CASE? replaces and extends CASE OF ENDOF ENDCASE For 18 years I have thought that CASE? is better than the Eaker CASE . ( -- Wil Baden Costa Mesa, California Per neilbawd@earthlink.net )
page written by:: mlg