How to make a backward compatible recipe?

[benoitchantre]

I would like to set a variable to store a binary path.

Deployer v7 has a new which function that doesn't exist in Deployer v6.
Deployer v6 has a locateBinaryPath function that doesn't exist in Deployer v7.

Here's what I tried without success.

// Return path to the `wp` bin.
set('bin/wp', function () {

    // Backward compatibility for Deployer 6
    if (function_exists('locateBinaryPath')) {
        return locateBinaryPath('wp');
    }

    return which('wp');
});

When this runs using Deployer 6, I get an error because the function which doesn't exist.

What did I miss?

Thank you for your help :-)