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Forth

1960's, USA


<Charles Moore>


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Description

FORTH is an interesting high-level language that has achieved some popularity. It is developed by Charles Moore in the 1960's, originally for use in control applications at an astronomical observatory.

Forth has a number of uncommon properties. All parameters and results are going through a DATA STACK which is present beside the normal RETURN STACK. In this way a sub programme can directly access its parameters and return more then one result. Forth does not know the usual 'Edit - Compile - Link - Go' cycle; the interpreter or compiler answers right away. Programming in Forth means to extend the command set. With Forth the user can virtually create a whole new set of instructions to suit the needs of the application. Also the compiler itself can be extended. And with this any DATA STRUCTURE is possible.

While developing Forth much attention was given to simplicity. The consequence: all parts of the system are accessible, transparent, and easy to adapt to one's needs.

Forth code is very small. A complete Forth system of Editor, Interpreter, Compiler and Assembler can stay under 8Kb. Comparing run time with Assembler or other well organized compilers Forth belongs to the slower echelons. While properties like two stacks and double indirect addressing of processors are not always supported. Because of this an Assembler is integrated with Forth so that time critical routines can be built in assembler. Forth is strong in areas where there's an empirical environment (e.g. real time applications). Less suitable is Forth when there is a more formalized situation then an efficient approach towards the machine. The Forth programmer has to his disposal a tool that speaks in all phases of the programme development the same language. Each word means an action. Forth is easy to update because the high level code is based on machine language routines and only these are to be written anew

One of the disadvantages of this flexibility is that there are many different dialects of Forth but in this year (1989) an ANSI standard is expected.

 

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