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The programming language Forth  
About postfix, infix and prefix.

KISS-commands in Forth

Many a Forth beginner has problems with reverse Polish notation (RPN). Not that this is an unsurmountable problem. Just do it and get used to it. Unfortunately the learning-curve can be steep, and only after a lot of practice it becomes evident what the benefits of RPN are. In other words, it can become a psychological stumbling block for impatient newbies.
There is hope: the program KISS.FRT enables Profane Notation in Forth. This is the solution all the world has been waiting for!

Of course, exactly those people that need it most won't be able to read the next program. Not a problem: simply skip to Defining KISS-commands. Programs work regardless whether they're being understood. 
Forth file:  ec212.frt
\ KISS COMMANDS (Albert Nijhof) -- 1 april 2003

FORTH DEFINITIONS   DECIMAL
VOCABULARY PARENTHESES
ALSO PARENTHESES DEFINITIONS

\ P-stack with relative stackpointer in cell # 0
12 CELLS CONSTANT pq
CREATE P   0 ,   PQ allot
: FRESH 0 P ! ;                 \ Reset p-stack
: ?P ( p# -- )   \ Check overflow and underflow
  PQ 0 WITHIN
  IF   FRESH TRUE ABORT" Syntax Error "
  THEN ;
: P> ( -- x ) P @ DUP CELL- DUP ?P P ! P + @ ;
: >P ( x -- ) P @ DUP ?P CELL+ DUP P ! P + ! ;
ALSO FORTH DEFINITIONS
: ) ( -- ) P> 2@                   ( xt imm? )
  0< STATE @ AND
  IF   COMPILE, EXIT
  THEN EXECUTE ; IMMEDIATE

: KISS ( ccc -- )
  >IN @ >R ' DROP       \ Does this word exist?
  R@ >IN ! BL WORD FIND R> >IN !      \ xt imm?
  CREATE  HERE 2 CELLS ALLOT 2! IMMEDIATE
  DOES>   >P
  BL WORD COUNT EVALUATE
  POSTPONE ) ;
: DUMMY ; IMMEDIATE
KISS DUMMY