Conflict with variables in pure functions

Question

Consider the following snippet of code.

Clear[f, g]
f[x_] := Function[{i}, x];
g[h_] := Module[{Z},
   Z[i_] := Print[h];
   Print[h];
   Z[1];
];

When g[f[2]] is called, the first Print correctly returns Function[{i$},2], while the second Print returns an error with Function[{1},2] as the output. The error arises from a conflict between the two local variables i's in f and Z. In general, Mathematica automatically renames variables to avoid conflict, as described here.

Why is there a conflict in this case? Other than choosing an alternative variable name, what are the useful guidelines one should follow to avoid such conflicts?

Answer 1

Using

SetSystemOptions["StrictLexicalScoping" -> True]

will fix this.

Related (long reading!):

• I define a variable as local to a module BUT then the module uses its global value! Why?

Answer 2

EDIT

 SetAttributes[g, HoldFirst]

will solve your conflict here. To make this plausible, look at this line inside of your Module:

 Z[i_]:=Print[h]

Without HoldFirst this will look for the Kernel like:

 Z[i_]:= Print[Function[{i}, 2]]

when h is set to f[2] := Function[{i},2], so the i inside of your functions definition is now by mistake recognizes as the pattern i_, what you dont want. With the Attribute HoldFirst the assignment effectively looks like this:

 Z[i_]:=Print[f[2]]

then in this case, i inside of f[2] is not recognizes as the Pattern i_ and you dont get these conflicts.

Here is the example:

SetAttributes[g, HoldFirst]
g[f[2]]

Out:

Function[{i$},2]

Function[{i$},2]