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From: graifer@net1.UUCP
Newsgroups: comp.lang.apl
Subject: Re: APL puzzle based on Unix' Escapes
Message-ID: <427@net1.UCSD.EDU>
Date: Sun, 1-Mar-87 23:57:59 EST
Article-I.D.: net1.427
Posted: Sun Mar  1 23:57:59 1987
Date-Received: Mon, 2-Mar-87 21:33:14 EST
References: <29000002@infbs.UUCP> <4000002@hpcvck.HP>
Reply-To: graifer@net1.UUCP (Dan Graifer)
Organization: U.C. San Diego
Lines: 28

In article <4000002@hpcvck.HP> paull@hpcvck.HP (Paul Liebert) writes:
>What about
>
>FUN {is assigned} 1 {drop} {nand} {scan} 1 {catenate} '\' {equals} STRING
>                 ^
>                {negate}
>

I tried this, and it didn't seem to work... I got two ones followed by a 
string of zeros almost all cases.  A little reflection revealed the 
error.  It is a result of a common confusion about the scan operator used
with non-associative diadic primitives.

if:
  R {is assigned} f\V
then
  R[I] {is assigned} f/I{take}V  for all I {element of} {iota}{rho}V
 and (this is the key) the COMPRESS EVALUATES RIGHT TO LEFT.

Thus,

    {nand}\1 1 0 0 0
1 0 0 1 1
    {comment} not 1 0 1 1 1 !
-- 
                              Dan Graifer
                              graifer@net1.UCSD.EDU
Disclaimer: Nobody ever listens to me anyways; Why should they start now?