Factored library, implemented make-continuation.

[scheme.forth.jl.git] / src / scheme-library-2-derived-forms.scm

diff --git a/src/scheme-library-2-derived-forms.scm b/src/scheme-library-2-derived-forms.scm
new file mode 100644 (file)
index 0000000..ba1e182
--- /dev/null
+++ b/src/scheme-library-2-derived-forms.scm
@@ -0,0 +1,144 @@
+;; DERIVED FORMS
+
+;; define
+
+(define-macro (define args . body)
+              (if (pair? args)
+                (list 'define (car args) (join-lists (list 'lambda (cdr args)) body))
+                'no-match))
+
+;; not
+
+(define-macro (not x)
+              (list 'if x #f #t))
+
+;; let
+
+(define-macro (let args . body)
+              (join-lists
+                (list (join-lists (list 'lambda (map (lambda (x) (car x)) args)) body))
+                (map (lambda (x) (car (cdr x))) args)))
+
+;; quasiquote/unquote (one nesting level only)
+
+((lambda ()
+   (define (qqhelper l)
+     (if (null? l)
+       l
+       (let ((head (car l))
+             (tail (cdr l)))
+
+         (if (pair? head)
+             (if (eq? (car head) 'unquote)
+                 (list 'cons (car (cdr head)) (qqhelper tail))
+                 (if (eq? (car head) 'unquote-splicing)
+                     (list 'join-lists (car (cdr head)) (qqhelper tail))
+                     (list 'cons (list 'quasiquote head) (qqhelper tail))))
+             (if (symbol? head)
+                 (list 'cons (list 'quote head) (qqhelper tail))
+                 (list 'cons head (qqhelper tail)))))))
+
+   (define-macro (quasiquote arg)
+                 (if (not (pair? arg))
+                   (list 'quote arg)
+                   (qqhelper arg)))))
+
+;; begin
+
+(define-macro (begin . sequence)
+              `((lambda () ,@sequence)))
+
+;; caddr etc.
+
+(define-macro (caar l) `(car (car ,l)))
+(define-macro (cadr l) `(car (cdr ,l)))
+(define-macro (cdar l) `(cdr (car ,l)))
+(define-macro (cddr l) `(cdr (cdr ,l)))
+(define-macro (caaar l) `(car (car (car ,l))))
+(define-macro (caadr l) `(car (car (cdr ,l))))
+(define-macro (cadar l) `(car (cdr (car ,l))))
+(define-macro (caddr l) `(car (cdr (cdr ,l))))
+(define-macro (cdaar l) `(cdr (car (car ,l))))
+(define-macro (cdadr l) `(cdr (car (cdr ,l))))
+(define-macro (cddar l) `(cdr (cdr (car ,l))))
+(define-macro (cdddr l) `(cdr (cdr (cdr ,l))))
+(define-macro (cadddr l) `(car (cdr (cdr (cdr ,l)))))
+
+;; let*
+
+(define-macro (let* args . body)
+              (if (null? args)
+                `(let () ,@body)
+                `(let (,(car args))
+                   (let* ,(cdr args) ,@body))))
+
+;; while
+
+(define-macro (while condition . body)
+              (let ((loop (gensym)))
+                `(begin
+                   (define (,loop)
+                     (if ,condition
+                       (begin ,@body (,loop))))
+                   (,loop))))
+
+;; cond
+
+((lambda ()
+   (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
+
+((lambda ()
+   (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
+
+((lambda ()
+   (define (expand-or-expressions expressions)
+     (let ((first (car expressions))
+           (rest (cdr expressions)))
+       (if (null? rest)
+           first
+           `(if ,first
+                #t
+                ,(expand-or-expressions rest)))))
+
+   (define-macro (or . expressions)
+     (if (null? expressions)
+         #f
+         (expand-or-expressions expressions)))))
+