; file: show.scm
; author: robert keller
; purpose: define the "show" wrapper
; For any expression exp 
;     (show exp)
; will print the expression exp after a message "showing value of " and
; return the value of exp.
; It can thus be wrapped around any expression that is evaluated for a value.
;
; Alternatively,  
;     (show-message msg exp)
; will print a specified message before the value
;
; The result of this wrapped expression is the same as the value
; of the expression itself there will be a side-effect of displaying
; the expression and its value.
;
; Once your program is debugged, the wrapped expression can be replaced
; with the original expression.
;
; Caution: This file adds to the following to the namespace: 
;     show, show-message, show-wrapper, show-message-wrapper

(define (show-wrapper msg1 value)
  (begin
    (display "showing value of ")
    (display msg1)
    (display ": ")
    (display value)
    (newline)
    value))

(define (show-message-wrapper msg value)
  (begin
    (display msg)
    (display ": ")
    (display value)
    (newline)
    value))

(define-macro (show expr)
  `(show-wrapper ',expr ,expr))

(define-macro (show-message msg expr)
  `(show-message-wrapper ,msg ,expr))