a question about pattern replacements
- To: mathgroup at smc.vnet.net
- Subject: [mg36163] a question about pattern replacements
- From: Sidney Cadot <sidney at jigsaw.nl>
- Date: Fri, 23 Aug 2002 21:34:55 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
Hi all,
While playing arounf with patterns and substitutions, I came across the
following behavior which I didn't expect:
z := SomeHead[{{1, 2}, {3, 4}}]
z /. {SomeHead[q_] -> Flatten[q]}
While this _does_ yield the desired result {1,2,3,4}, Mathematica complains:
Flatten::"normal": Nonatomic expression expected at position 1 in
Flatten[q].
........as if it is trying to evaluate Flatten[q], with q not bound to
{{1,2},{3,4}}.
Could anybody explain why this happens?
Best regards,
Sidney Cadot