3.1 Compiler vs. Interpreter
An interpreter translates some form of source code into a target representation that it can
immediately execute and evaluate. The structure of the interpreter is similar to that of a
compiler, but the amount of time it takes to produce the executable representation will vary as
will the amount of optimization. The following diagram shows one representation of the
differences.
Compiler characteristics:
•spends a lot of time analyzing and processing the program
•the resulting executable is some form of machine- specific binary code
•the computer hardware interprets (executes) the resulting code
•program execution is fast
Interpreter characteristics:
•relatively little time is spent analyzing and processing the program
•the resulting code is some sort of intermediate code
•the resulting code is interpreted by another program
•program execution is relatively slow
The above characteristics are typical. There are well-known cases that are somewhere in
between, such as Java with it's JVM.
Interpreters
An interpreter is also a program that translates a high-level language into a low-
level one, but it does it at the moment the program is run. You write the program
using a text editor or something similar, and then instruct the interpreter to run the
program. It takes the program, one line at a time, and translates each line before
running it: It translates the first line and runs it, then translates the second line and
runs it etc. The interpreter has no "memory" for the translated lines, so if it comes
across lines of the program within a loop, it must translate them afresh every time
that particular line runs. Consider this simple Basic program:
10 FOR COUNT = 1 TO 1000
20 PRINT COUNT * COUNT
30 NEXT COUNT
Line 20 of the program displays the square of the value stored in COUNT and this
line has to be carried out 1000 times. The interpreter must also translate that line
1000 times, which is clearly an inefficient process. However, interpreted languages
do have their uses, as we will see in a later section.
Examples of interpreted languages are Basic, JavaScript and LISP.
Well, that depends on how you want to write and run your program. The main
advantages of compilers are as follows:
