Interpreter and Compiler
Let's introduce at this point some concepts of execution of programs written in high level programming languages. As we have already seen, the only language that a computer can understand is the so called machine language. These languages are composed of a set of basic operations whose execution is implemented in the hardware of the processor. We have also seen that high level programming languages provide a machine-independent level of abstraction that is higher than the machine language. Therefore, they are more adapted to a human-machine interaction. But this also implies that there is a sort of translator between the high level programming language and the machine languages. There exists two sorts of translators:
Interpreter
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| An Interpreter is a program that implements or simulates a virtual machine using the base set of instructions of a programming language as its machine language. You can also think of an Interpreter as a program that implements a library containing the implementation of the basic instruction set of a programming language in machine language. An Interpreter reads the statements of a program, analyzes them and then executes them on the virtual machine by calling the corresponding instructions of the library. | |
Interactive interpreter session
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During an interactive interpreter session the statements are not only read, analyzed and executed but the result of the evaluation of an expression is alsoprinted. This is also called a READ - EVAL - PRINT loop.
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Compiler
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| A Compiler is a program that translates code of a programming language in machine code, also called object code. The object code can be executed directly on the machine where it was compiled. | |
So using a compiler separates translation and execution of a program. In contrast of an interpreted program the source code is translated only once.
The object code is machine-dependent meaning that the compiled program can only be executed on a machine for which it has been compiled, whereas aninterpreted program is not machine-dependent because the machine-dependent part is in the interpreter itself.