.oO(2metre)

>I accept that the definition of compiler is open to debate.
>
>I was using the concept that 'compiling' infers converting the entire
>'human-readable' source file into a 'machine-readable' executable file (
>which can then be 'run'). By this definition, PHP is not a compiler.

A compiler doesn't create executable files, that's what the linker does.
A compiler translates one language/grammar into another, in case of PHP
it translates the source code into a bytecode. This bytecode is then
executed by an interpreter.

>Using the definition favoured by you and the OP:
>With an interpreted language like PHP, if a function is never called or
>an object/class definition never used, it doesn't get compiled.

I don't know, this would require to have a deeper look at PHP's core.

Micha