Custom Functions: passing with env map to Run or creating in Compile with expr.Function

[aldas]

1. Which is the recommended way to deal with custom functions.
   a) passing with env map to Run
   b) creating in Compile with expr.Function

2. Is there a performance difference?

[antonmedv]

Which is the recommended way to deal with custom functions.

Expr has three ways to define function: via map, via methods on env struct, via expr.Function.

Is there a performance difference?

The fastest way is via expr.Function.

[aldas]

Expr has three ways to define function: via map, via methods on env struct, via expr.Function.

In which situation you prefer use which one? Maybe some example of some situation where one is more suitable than the others?
Is there functional difference?

[antonmedv]

It depends on your data structures. For example, Order{} structure.