~ Expression evaluation
( "!: " #G,c; 1 c. '. = - ^
   #E,c; ! )
$E #T,1%;                      ~ Evaluate an expression
   1%. '+ =
      [ #G,1%; #E,1%; + @ ]
   1%. '- =
      [ #G,1%; #E,1%; - @ ] @
$T #F,1%;                      ~ Evaluate a term
   1%. '* =
      [ #G,1%; #T,1%; * @ ]
   1%. '/ =
      [ #G,1%; #T,1%; / @ ]
   1%. '\ =
      [ #G,1%; #T,1%; \ @ ] @
$F #D,1%;                      ~ Evaluate a factor
      [ #N,1%; @ ]
   1%. '( =
      [ #G,1%; #E,1%;
         1%. ') =
            [ #G,1%; @ ]
         "!) expected" @ ]
   " Illegal character!:" 0 @
$N 1%. '0 -                    ~ Convert digit string to number
   ( #G,1%; #D,1%; ^
      10 * 1%. '0 - + ) @
$D 1%. x:                      ~ Digit test
   x. '0 1 - >
   x. '9 1 + < * @
$G ( ?' x: x. ' =              ~ Get a non-blank character
   x. 13 = + x. 10 = + ^ )
   x. 1%: @