A high-level programming language translator that translates and runs the program at the same time. It converts one program statement into machine language, executes it, and then proceeds to the next statement. This differs from regular executable programs that are presented to the computer as binary-coded instructions. Interpreted programs remain in the source language the programmer wrote in, which is human readable text.
Slower, But Easier to Test
Interpreted programs run slower than their compiler counterparts. Whereas the compiler translates the entire program before it is run, interpreters translate a line at a time while the program is being run. However, it is very convenient to write an interpreted program, since a single line of code can be tested interactively.
Some languages can be both interpreted and compiled, in which case a program may be developed with the interpreter for ease of testing and debugging and later compiled for production use. See JIT compiler.
The Runtime Interpreter Must Be Present
Interpreted programs must always be run with the interpreter, commonly called a runtime module. For example, in order to run a BASIC or Foxbase program, the BASIC or Foxbase interpreter must be running as well.
Interpreted Vs. Intermediate Languages
Interpreted languages also differ from intermediate languages such as Java, which are partially converted but still require a runtime module (see Java and Java virtual machine).
Interpreters and Compilers
Unlike compiled languages which are translated into machine language ahead of time (right), interpreted languages are translated at runtime. dBASE and BASIC interpreters (middle) translate the original source code. Java and Visual Basic (left) interpreters translate "bytecode," which is an intermediate language compiled from the original source code.