forte

A stack-based, forth-like, esoteric programming language, read about Forth on Wikipedia.
Inspired by BrainFart, a BrainFuck interpreter.

Instructions

Opcode	Stack effect
number literal	push the number into the stack
+	( i j -- o ) where o := i + j add
-	( i j -- o ) where o := i - j subtract
*	( i j -- o ) where o := i * j multiply
/	( i j -- o ) where o := i / j divide
%	( i j -- o ) where o := i % j reminder
=	( i j -- o ) where o := i = j equal
>	( i j -- o ) where o := i > j greater
<	( i j -- o ) where o := i < j less
~	( i -- o ) where o := ~i bitwise not
&	( i j -- o ) where o := i & j bitwise and
^	( i j -- o ) where o := i ^ j bitwise xor
|	( i j -- o ) where o := i | j bitwise or
«	( i j -- o ) where o := i << j shift left
»	( i j -- o ) where o := i >> j shift right (signed)
.	( i -- ) pop
_	( i -- i i ) duplicate
,	( i j -- j i ) swap
?	( -- i ) ask (wait for incoming byte from stdin)
!	( i -- ) say (output value as char)
¡	( i -- ) print (output value as number)
[	( i -- ) move i into the loop stack. Loop while i != 0 see implementation details
]	ends the matching loop see implementation details
{	( i -- ) start function definition see implementation details
}	end function definition see implementation details
@	( i -- ) call function see implementation details
$	return
§	halt

Implementation details

Every character not listed in opcodes is ignored and will be treated as a comment.

• number literal

  42 42-
  

  Pushes 42 and -42 onto the stack

  Note: in this context spaces are important!

  42 42 -
  

  The code above pushes 2 times the number 42 into the stack, then subtracts the latters and pushes the result back.

• loops

  Forte has a special stack called loop stack in which loop control values are pushed after being removed from the data stack.

  At each iteration the current loop control value will be updated to next value toward 0.

   10 97  2 [ ! ]
   10 97 -2 [ ! ]
  

  both lines above produce the same output: "a\n"

• functions definitions/calls

  In forte a function is identified by a number.

  { will pop the value on top of the stack and that value is used for identifing the function.

  In order to call a function a similar operation is done: @ will pop the top of the stack to determine the function to call.

  0{
    21 21 +
  }
  
  0@
  

  Note that functions can be redefined, and there are no undefined-functions: by default every identifier points to a no-op function.

  42@    \\ noop
  
  42{    \\ define function 42
    21 21 +
  }
  
  42{    \\ redefine function 42
    20 20 2 + +
  }