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Re: [Bug-apl] Outer product with replicate error

From: Juergen Sauermann
Subject: Re: [Bug-apl] Outer product with replicate error
Date: Sun, 15 May 2016 11:29:45 +0200
User-agent: Mozilla/5.0 (X11; Linux i686; rv:31.0) Gecko/20100101 Thunderbird/31.4.0


even though outer product dates back to the early days of APL, if I remember correctly then
you could only use it with scalar functions, not with mixed functions at that time.

Therefore I believe that ∘./ would have given a SYNTAX ERROR even in the early days
(mainly because you would have needed nested arrays to represent the result).

/// Jürgen

On 05/15/2016 03:49 AM, David B. Lamkins wrote:
While `$ info apl` speaks to the issues around function/operator ambiguity, it does not make any mention of the outer product case.

I suspect that the failure of "outer product expand" is an oversight. This case is disambiguated by noticing the outer product during the right-to-left scan that GNU APL does anyway (step 3 in the referenced info page).

Outer product is a common idiom dating from the earliest days of APL. It doesn't make any sense to require special (i.e. specific to GNU APL) syntax for this particular case.

On Sat, May 14, 2016 at 01:31:13PM -0500, Xiao-Yong Jin wrote:

On May 14, 2016, at 7:51 AM, David Tran <address@hidden> wrote:


Newbie study "MasteringDyalogAPL"; got error on page #388 example:

      3 0 2 ∘./ 5 1 7
      3 0 2∘./5 1 7
      ^      ^

bug? ( or this is a specify feature of Dyalog and not APL2 ? )
It’s documented in the info page of gnu apl.  A feature (bug?) of the parser treats / as an operator in this case.  Simple workaround would be

      3 0 2 ∘.{⍺/⍵} 5 1 7
 5 5 5  1 1 1  7 7 7 
 5 5    1 1    7 7   

I have too limited experience to say whether it is good or bad.  Perhaps the parser should accept some exceptional cases?


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