Switch and List
- To: mathgroup at yoda.physics.unc.edu
- Subject: Switch and List
- From: HAY at leicester.ac.uk
- Date: Thu, 30 JAN 92 12:02:54 GMT
There are problems with using ReplaceAll: it can replace to much -
In[] Release[Hold[Switch[a,{a,{va}}]]/.List->Sequence]
Out[] va
Wrong: we wanted {va}
In[] Release[Hold[Switch[{a},{a,va}]]/.List->Sequence]
Out[] va
Wrong: a does not match {a}.
Using ReplacePart instead of ReplaceAll corrects these and maybe faster:
In[] Release[
ReplacePart[
Hold[Switch[a,{a,{va}}]],
Sequence, {1,2,0}
]
]
Out[] {va}
In[] Release[
ReplacePart[
Hold[Switch[{a},{a,va}]],
Sequence, {1,2,0}
]
]
Out[] Switch[{a}, a, va, b, vb]
From
Allan Hayes
Department of Mathematics
The University
Leicester LE1 7RH
U.K.
hay at leicester.ac.uk