This question already has an answer here:
I would like to create a function that acts on whether the input is even or odd, e.g.:
In:= f[a_] = If[EvenQ[a], 2 a, 3 a]; f Out= 6
I've determined (I think) that this is because
a is an expression and
QEven returns false for expressions. How do I hold off evalution of this until input is given? I thought something like
Defer would work but then it is never evaluated (see below)!
In:= g[a_] = If[Defer[EvenQ[a]], 2 a, 3 a] Out= If[EvenQ[a], 2 a, 3 a] In:= g Out= If[EvenQ, 2 * 3, 3 * 3]
Apologies if this gets asked a lot - I assume this is a common issue, but I was unable to come up with appropriate search terms to describe it (I'm not very familiar with Mathematica terminology yet). Thanks!