; Operational semantics for binary numbers, patterned after the attribute
; grammar and denotational definitions in
; ../semantics-expamples/binary-numbers{attr,deno}, q.q.v.
;
; Syntactically, a binary number is represented as a list of 0's and 1's, with
; an optional decimal point.  E.g., ( 1 1 0 1 \. 0 1 ).

(defun main ()
    (let ((number (read)))
        (eval-binary-number number)
    )
)

(defun eval-binary-number (number)
    (let* ((integer-value (eval-integer-part number 0))
           (number (move-upto-dot number))
           (fractional-value (eval-fractional-part number 0)))
        (+ integer-value fractional-value)
    )
)

(defun eval-integer-part (number val)
    (cond ( (or (null number) (eq (car number) '\.))
            val )
          ( t
            (let* ((val (+ (* 2 val) (car number))))
                (eval-integer-part (cdr number) val)) )
    )
)

(defun eval-fractional-part (number val)
    (cond ( (null number)
            val )
          ( t
            (let* ((val (/ (eval-fractional-part (cdr number) val) 2.0)))
                (+ (/ (car number) 2.0) val)) )
    )
)

(defun move-upto-dot (number)
    (cond ( (null number)
            nil )
          ( (eq (car number) '\.)
            (cdr number) )
          ( (or (eq (car number) 0) (eq (car number) 1))
            (move-upto-dot (cdr number)) )
    )
)