Quite often a programmer needs to switch the numerical base for just a word or a number. In the worst case this involves saving the old BASE, setting BASE to the wanted value and then restoring the old BASE. A lot of code for just one word/definition.

The routine FFBASE enables the creation of precursor words which, just for the next definition or number, temporarily set the base to another.

So, for instance:

    16 FFBASE HX

Creates a word, called HX that will set the numeric base to 16, but ONLY for the word following it. It deals correctly with definitions being compiled, definitions being executed and values.

The name FFBASE, by the way, came from the Dutch word 'even'. It means 'for a short while'. This in colloquial language is pronounced 'effen', which is also the plural of 'F'. So FFBASE in Dutch is pronounced 'EffenBase' and it gives a different numeric base for a very short while.

It should be mentioned that in this phrase : .hex hx . ; the BASE is set to hex while . (dot) is compiled, but not at runtime! So this HX has no effect.

Function: (BASE) ( XT temporary_base -- )
  execute an XT using a temporary base - used by FFBASE
  
Function: FFBASE
  CREATE: ( base ccc -- ) create a precursor word 'ccc' with 'base'
  DOES>: ( ccc -- )
        {get base from definition} 
        {find ccc in dictionary}
        {get state}
        IF compiling and ccc=not_immediate
            {compile XT and temp_base as literals and postpone (BASE)
        IF interpreting or ccc=immediate
            {call (BASE) with XT and temp_base on stack}
        IF not found in dictionary
            {convert to number using temp_base and put on stack}

Definitions assumed to be available in your Forth: WORD, EVALUATE, COUNT

See separate file: FFBASE sample implementation

The generic Forth version should run on the majority of Forth implementations. It is successfully tested on iForth and wabiForth. However in the present form it does not run on MeCrisp for reasons unknown to me.

Alternative Implementations