;; All implementations here are "borrowed" from 
;; husk-scheme (github.com/justinethier/husk-scheme).
(define-syntax let
    (syntax-rules ()
        ((_ ((x v) ...) e1 e2 ...)
            ((lambda (x ...) e1 e2 ...) v ...))
        ((_ name ((x v) ...) e1 e2 ...)
            (let*
                ((f (lambda (name)
                    (lambda (x ...) e1 e2 ...)))
                (ff ((lambda (proc) (f (lambda (x ...) ((proc proc)
                        x ...))))
                    (lambda (proc) (f (lambda (x ...) ((proc proc)
                        x ...)))))))
                (ff v ...)))))

(define-syntax let*
    (syntax-rules ()
       ((let* () body1 body2 ...)
        (let () body1 body2 ...))
       ((let* ((name1 val1) (name2 val2) ...)
          body1 body2 ...)
        (let ((name1 val1))
          (let* ((name2 val2) ...)
            body1 body2 ...)))))

(define-syntax letrec
  (syntax-rules ()
                ((letrec ((var1 init1) ...) body ...)
                 (letrec "generate_temp_names"
                   (var1 ...)
                   ()
                   ((var1 init1) ...)
                   body ...))
                ((letrec "generate_temp_names"
                   ()
                   (temp1 ...)
                   ((var1 init1) ...)
                   body ...)
                 (let ((var1 #f) ...)
                   (let ((temp1 init1) ...)
                     (set! var1 temp1)
                     ...
                     body ...)))
                ((letrec "generate_temp_names"
                   (x y ...)
                   (temp ...)
                   ((var1 init1) ...)
                   body ...)
                 (letrec "generate_temp_names"
                   (y ...)
                   (newtemp temp ...)
                   ((var1 init1) ...)
                   body ...))))

(define-syntax do
    (syntax-rules ()
        ((_ ((var init . step) ...)
                (test expr ...)
            command ...)
            (let loop ((var init) ...)
                (if test
                    (begin expr ...)
                        (begin (begin command ...)
                            (loop
                                (if (null? (cdr (list var . step)))
                                    (car (list var . step))
                                    (cadr (list var . step))) ...)))))))