-;; LIBRARY SPECIAL FORMS
-
-; let
-
-(define (let-vars args)
- (if (null? args)
- '()
- (cons (caar args) (let-vars (cdr args)))))
-
-(define (let-inits args)
- (if (null? args)
- '()
- (cons (cadar args) (let-inits (cdr args)))))
-
-(define-macro (let args . body)
- `((lambda ,(let-vars args)
- ,@body) ,@(let-inits args)))
-
-; while
-
-(define-macro (while condition . body)
- (let ((loop (gensym)))
- `(begin
- (define (,loop)
- (if ,condition
- (begin ,@body (,loop))))
- (,loop))))
-
-; cond
-
-(define (cond-predicate clause) (car clause))
-(define (cond-actions clause) (cdr clause))
-(define (cond-else-clause? clause)
- (eq? (cond-predicate clause) 'else))
-
-(define (expand-clauses clauses)
- (if (null? clauses)
- (none)
- (let ((first (car clauses))
- (rest (cdr clauses)))
- (if (cond-else-clause? first)
- (if (null? rest)
- `(begin ,@(cond-actions first))
- (error "else clause isn't last in cond expression."))
- `(if ,(cond-predicate first)
- (begin ,@(cond-actions first))
- ,(expand-clauses rest))))))
-
-(define-macro (cond . clauses)
- (if (null? clauses)
- (error "cond requires at least one clause.")
- (expand-clauses clauses)))
-
-; and
-
-(define (expand-and-expressions expressions)
- (let ((first (car expressions))
- (rest (cdr expressions)))
- (if (null? rest)
- first
- `(if ,first
- ,(expand-and-expressions rest)
- #f))))
-
-(define-macro (and . expressions)
- (if (null? expressions)
- #t
- (expand-and-expressions expressions)))
-
-; or
-
-(define (expand-or-expressions expressions)
- (if (null? expressions)
- #f
- (let ((first (car expressions))
- (rest (cdr expressions))
- (val (gensym)))
- `(let ((,val ,first))
- (if ,val
- ,val
- ,(expand-or-expressions rest))))))
-
-(define-macro (or . expressions)
- (expand-or-expressions expressions))
-
-