Perl 在编译时和运行时如何反应？

Question

What my understanding over this would be:

During compile time , an error is one that keeps Perl from being able to parse the file; such as a missing semi-colon.

And a run time error is an error that can not be detected until the code is run; such as a divide by zero error or a call to an undefined subroutine.

As Perl is an interpreted language, will the entire code or script be complied once and then run or will it compile for each and every line and then go for run?

What is the explanation?

Answer 1

The program will be compiled once into an optree. The optree is traversed and executed.

At runtime, it can happen that additional compile phases become necessary. The usual culprits are string eval and delayed/dynamic loading of code units, eg require , do .

Answer 2

Perl is an interpreted language, which means that both the compile phase and the run phase happen in sequence every time you attempt to start a script.

Compiled languages on the other hand (C, Pascal, etc) separate out those two phases, and typically have an intermediate phase called linking , which joins together object files and libraries into the final executable file.

In compiled languages, detecting an undefined function can happen in either the compile phase, or the linking phase, depending on how strict the language specification is. In original C calling an undefined function would be found by the linker, but in C++ it would be found by the compiler.

To further complicated matters, some languages such as Java have separate compile and execution phases, but the compilation is actually to an intermediate "byte code", which is then interpreted by a run time system (ie the Java Virtual Machine).

Strictly speaking, Perl also uses an intermediate byte code, but the separation of the phases is mostly invisible.