Anyway to define and use other utilities function within the lambda functions?

Just wondering how do I pass/declare a helper function to the kernel function so they can be used within BOOST_COMPUTE_FUNCTION or BOOST_COMPUTE_CLOSURE.

I saw the BOOST_COMPUTE_DECLARE_BUILTIN_FUNCTION macro but not quite sure how to use it or even if it is the correct way to declare a new function that is accessible from within a lambda.

Something in the range of this example, basically trying to inline this foo() into bar().
```
inline float foo()
{
return -1.0f;
}

BOOST_COMPUTE_FUNCTION(float, bar, (float in),
{
return in + foo();
})
```

Any advise is appreciated, thanks.