K-user mailing list

["Chen, Xiaohong" <xc3 AT illinois.edu>]

Hi Derek,

The pattern you wrote needs associative and commutative matching (AC 
matching), 
which is not fully supported. 

You could define an auxillary function that scan the list and pick an element,
in the standard functional programming head::tail style, or create a new cell
and put your list there. Then you could write
  rule <cell> ... X => something ... <\cell>
as AC matching in cells is supported.

Best,
Xiaohong

-------------------------
Chen, Xiaohong
BSc, Peking University
PhD student, UIUC

________________________________________
From: Derek Sorensen 
[derek AT pyrofex.net]
Sent: Wednesday, August 15, 2018 5:19 PM
To: 
k-user AT lists.cs.illinois.edu
Subject: [[K-user] ] Choose something in the middle of a list

Hi all,

I’m trying to tell K5 to choose an element of a list, saying that it could be 
anywhere in the list. In K3.4 I could just write as a pattern

        ListHead:List ListItem(X) ListTail:List

and K would match this pattern if X was anywhere in the list, since ListHead 
or ListTail could be potentially empty. K5 doesn’t let me do that; it returns 
an error saying “Unsupported associative matching on list.” Is there any way 
to choose something out of a list without needing it to be the first or last 
element?

Thanks,
Derek