## 3 Problem Example

### 3.1 Description

A common interoperability situation is when there exists a piece of code solving some complex problem, and we would like to incorporate this piece of code in our Erlang program. Suppose for example we have the following C functions that we would like to be able to call from Erlang.

    /* complex.c */

    int foo(int x) {
      return x+1;
    }

    int bar(int y) {
      return y*2;
    }

(For the sake of keeping the example as simple as possible, the functions are not very complicated in this case).

Preferably we would like to able to call `foo` and `bar` without having to bother about them actually being C functions.

    % Erlang code
    ...
    Res = complex:foo(X),
    ...

The communication with C is hidden in the implementation of `complex.erl`. In the following chapters it is shown how this module can be implemented using the different interoperability mechanisms.

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