JAL manual - language - expressions

An expression is constructed from literals, identifiers, function calls and operators. An identifier can identify a constant, a variable or (within a subprogram) a formal parameter.

The predefined operators are:

operator	priority	interpretation	left argument	right argument	result
!	5	monadic not		bit	bit
!	5	monadic not		byte	byte
+	5	monadic plus		byte	byte
-	5	monadic minus		byte	byte
*	4	multiplication	byte	byte	byte
/	4	division	byte	byte	byte
%	4	modulo	byte	byte	byte
+	3	plus	byte	byte	byte
-	3	minus	byte	byte	byte
<<	2	shift left	byte	byte	byte
>>	2	shift right	byte	byte	byte
>	2	larger than	byte	byte	bit
<	2	less than	byte	byte	bit
>=	2	larger than or equal	byte	byte	bit
< =	2	less than or equal	byte	byte	bit
==	2	equal	byte	byte	bit
!=	2	not equal	byte	byte	bit
&	1	and	bit	bit	bit
&	1	and	byte	byte	byte
|	1	or	bit	bit	bit
|	1	or	byte	byte	byte
^	1	xor	bit	bit	bit
^	1	xor	byte	byte	byte

The operators which are predefined can (for the same arguments) not be redeclared, so these operators have a fixed meaning. Other operators can be declared and redeclared by the user.

All operators which operate on bytes can also operate on universals. When the result from byte arguments is byte, the result from univeral arguments will be universal. When the result from byte arguments is bit, the result from univeral arguments will also be bit.

examples:

   var byte a = 1 << n
   if ( a > b ) | ( c < d ) | ( x != y ) then 
      x = ( x & 0b_1100_0011 ) | 0b_0001_0100
   end if

Braces can be used to force the association, otherwise the operator's associate with their arguments according to operator's priority. For operators of equal priority the leftmost operator gets higher precedence.

examples:

   var byte x = ! a + b   -- is ( ! a ) + b
   var y = ! ( a + b )   -- () used to force another interpretation

The order in which independent parts of an expression are evaluated is not defined. A part of an expression might be evaluated more than once, a part which has no influence on the overall value of an expression might not be evaluated at all. Functions with side effects can make this behaviour noticable.

examples:

   var byte n = 1
   function f return byte is
      n = n + 1
      return 3
   end function

   function g return byte is
      n = 2 * n
      return 4
   end function

   var byte a = f + g

   if n == 4 then
      -- might be executed, but don't count on it
   end if