Editing Dynamic compilation (section)

==Incremental compilation==
A closely related technique is '''incremental compilation'''. An [[incremental compiler]] is used in [[POP-2]], [[POP-11]], [[Forth (programming language)|Forth]], some versions of [[Lisp (programming language)|Lisp]], e.g. [[Maclisp]] and at least one version of [[ML (programming language)|ML]] ([[Poplog]] ML).

This requires the [[compiler]] for the programming language to be part of the runtime system. In consequence, source code can be read in at any time, from the terminal, from a file, or possibly from a data-structure constructed by the running program, and translated into a machine code block or function (which may replace a previous function of the same name), which is then immediately available for use by the program. Because of the need for speed of compilation during interactive development and testing, the compiled code is likely not to be as heavily optimised as code produced by a standard 'batch compiler', which reads in source code and produces object files that can subsequently be linked and run. However an incrementally compiled program will typically run much faster than an [[interpreted language|interpreted]] version of the same program. Incremental compilation thus provides a mixture of the benefits of interpreted and compiled languages. To aid portability it is generally desirable for the incremental compiler to operate in two stages, namely first compiling to some intermediate platform-independent language, and then compiling from that to machine code for the host machine. In this case porting requires only changing the 'back end' compiler. Unlike dynamic compilation, as defined above, incremental compilation does not involve further optimisations after the program is first run.