Is Perl a compiled or an interpreted programming language?

Question

Is Perl compiled or interpreted?

Answer 1

You aren’t going to get a definite answer, because you haven’t provided a definite question.

Perl is always in one of two states: it is either compiling, or it is executing. That’s why you see talk of “at compile-time” vs “at run-time”. Normally, you get one compile phrase followed by one execution phase, but it need not be that way.

These two phases can also trade back and forth. An eval STRING is a way for the interpreter to call the compiler (so too therefore are do FILE and require). A BEGIN block is a way for the compiler to call the interpreter (so too therefore are use and no).

When you run perl -c, you omit the run-time phase. There are various ways to skip the compile-time phase, but none of them is particularly convenient, or commonplace. Apache’s mod_perl only compiles scripts once but executes them many times. If you use the Byteloader, you can do the same. Et cetera.

The correct answer to whether Perl is compiled or interpreted is simply YES.

Answer 2

Well, that depends on what you mean by a compiled language. Maybe this is why googling did not bring forth a clear answer to your question.

One viewpoint is that compilation means compiling from a source code description to another, i.e. code generation.

If we accept these premises, then Perl 6 can be compiled and Perl 5 and older are interpreted languages.

Perl 6 is specifically compiled to Parrot bytecode. Perl 6 is therefore a properly compiled language, in the same way say, Java is.

Perl 5 and older parses the Perl source code to an internal list or tree, but I don't think it should be called a proper compiler, except maybe in a theoretical sense. It does not output any bytecode, assembly or real machine code usually associated with compilers. The parsing stage of Perl to check Perl syntax used to be called "compiling" the source. It is used to check the syntactical validity of a Perl source file without running it.

It is invoked as:

perl -c myprog.pl 

But if you look at the help for Perl options, -c actually stands for "check".

-c                check syntax only (runs BEGIN and CHECK blocks) 

^{(To further complicate things, Perl 5 had support for writing out internal bytecode but it was removed in version 5.10. Presumably because it was buggy, I don't know.)}

On the other hand, if you argue that compilation is the act of parsing a source tree into any other kind of representation, well, that parsing makes Perl a compiled language. Perl must completely parse a source file before it can start executing it. By this definition, any language which can start executing a source file immediately before parsing would be an interpreted language.

A third way to look at this is from how these words, "interpreted" and "compiled" are most often used by professionals in the field. I would bet good money that if a random subset of programmers were asked to choose "compiled" or "interpreted" when thinking of Perl, most would choose "interpreted". Not because of some theoretical argument over the nature of Perl, but because "compiled" usually invokes thoughts of "compiling", "linking", "object code" etc, while "interpreted" is taken to mean "write the code, try it". Right or wrong, that may be good to know when trying to determine if Perl is, truly, interpreted or in fact, compiled. You are going to run into many arguments on your quest.