plet*   scheme

;; Like c{plet}, but each subsequent pattern-datum pair is evaluated in an environment
;; with all previous matches bound.
;; <pre>
#|
(plet* ((p1 d1)
        (p2 d2)
        ...
        (pn dn))
       e1
       e2
       ...)
|#
;;</pre>
;; is equivalent to
;; <pre>
#|
(plet ((p1 d1))
      (plet ((p2 d2))
            ...
            (plet ((pn dn)
                   e1
                   e2
                   ...)))).
|#
;; </pre>
;; @args ({(pattern datum)}) body
(define-syntax plet*
  (er-macro-transformer
   (lambda (expr rename compare)
     (let ((pattern-pairs (cadr expr))    ; pattern-pairs := {(pattern_i datum_i)}
           (body          (cddr expr)))   ; body of the plet* (everything after pattern-pairs)
       (cond ((null? pattern-pairs) `(let () ,@body)) ; no patterns to match, i.e. (plet () body)
             (else ; at least one pattern to match
              `(plet ,(list (car pattern-pairs))
                     (plet* ,(cdr pattern-pairs)
                            ,@body))))))))