### 4.1 Introduction

GNU Prolog offers two ways to execute a Prolog program:

- interpreting it using the GNU Prolog interactive interpreter.
- compiling it to a (machine-dependent) executable using the GNU Prolog native-code compiler.

Running a program under the interactive interpreter allows the user to list it and to make full use of the debugger on it (section 5). Compiling a program to native code makes it possible to obtain a stand alone executable, with a reduced size and optimized for speed. Running a Prolog program compiled to native-code is around 3-5 times faster than running it under the interpreter. However, it is not possible to make full use of the debugger on a program compiled to native-code. Nor is it possible to list the program. In general, it is preferable to run a program under the interpreter for debugging and then use the native-code compiler to produce an autonomous executable. It is also possible to combine these two modes by producing an executable that contains some parts of the program (e.g. already debugged predicates whose execution-time speed is crucial) and interpreting the other parts under this executable. In that case, the executable has the same facilities as the GNU Prolog interpreter but also integrates the native-code predicates. This way to define a new enriched interpreter is detailed later (section 4.4.5).

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