#lang scheme

(require htdp/big-draw
         htdp/draw-sig
         mzlib/unit)

(define-syntax (draw s)
  (syntax-case s (produce)
    [(_ stmt ... produce exp) (syntax (begin (and stmt ...) exp))]
    [(_ stmt ... produce) 
     (raise-syntax-error #f "produce must be followed by an expression" s)]
    [(_ stmt ... produce exp exp2)
     (raise-syntax-error #f "produce must be followed by exactly one expression" s)]
    [(_ stmt ... produce exp exp2 exp3)
     (raise-syntax-error #f "produce must be followed by exactly one expression" s)]
    [(_ stmt ...)
     (raise-syntax-error #f "use drawing instructions between _draw_ and _produce_ and an expression behind produce" s)]
    ))

(provide 
 draw ;; (draw <expression> ... produce <expression>)
 )

(provide-signature-elements draw^)