How to define an auxiliary function within a function

Question

I would like to define a function within a function to serve as an auxiliary function. In essence, something like this:

f[x_,y_]:=Module[{g[z_]:=2z},x+g[y]]

Where both f and g are in reality complicated functions. But this does not work because Module, or With, do not accept rule delayed in their definitions.

f[1,2]
Module::lvset: Local variable specification {g[z_]:=2 z} contains g[z_]:=2 z, which is an assignment to g[z_]; only assignments to symbols are allowed.

Is there a way around it?

Check the second example in documentation for Module... – Kuba Jun 08 '17 at 09:43 — Kuba, Jun 08 '17 at 09:43

score 4 · Accepted Answer · answered Jun 08 '17 at 09:42

4

If you want, you can use

f[x_, y_] := Module[{g}, g[z_] := 2 z; x + g[y]]

answered Jun 08 '17 at 09:42

Kiro

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How to increase reputation fast: answer the easy questions before they get marked as duplicates :p – Kiro Jun 08 '17 at 11:35

How to define an auxiliary function within a function

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