How does the code idiom for replacing part of a held expression work?

Asked Nov 05 '17 at 16:14

Active Nov 05 '17 at 23:14

Viewed 51 times

I've seen this idiom used in different programs but never fully understand why it is necessary. Could someone explain? Is it still the recommended way to replace some part of a held expression to its evaluated value? Is there an alternative method that uses more built-in functionality?

heldExpression /: lhs_ :> evaluate[rhs_] := lhs :> With[{tmp = rhs}, tmp /; True]

edited Nov 05 '17 at 23:14

m_goldberg

107,779
16
103
257

asked Nov 05 '17 at 16:14

user13253

8,666
2
42
65

1

The earliest mention of that that I know of is at http://library.wolfram.com/infocenter/Conferences/377/ – Ted Ersek Nov 05 '17 at 18:09

How does the code idiom for replacing part of a held expression work?

0 Answers0