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unlc.scm
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unlc.scm
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;; Unlambda code generator
(define-module unlc
(use srfi-1)
(use file.util)
(use util.match)
(use text.tree)
(export defmacro defrecmacro add-unl-macro!
defsyntax add-unl-syntax!
print-as-unl compile-to-string compile-to-file)
)
(select-module unlc)
(define-macro (atom? x)
`(not (pair? ,x)))
(define (eliminate-lambda-rec x)
(match x
(('lambda-rec name args body)
`((lambda (x) (x x))
(lambda (,name ,@args)
,(eliminate-lambda-rec
(macroexpand (list (cons name (lambda (args)
(append (list name name) args))))
body)))))
(?-
(if (or (atom? x) (null? x))
x
(map eliminate-lambda-rec x)))))
(define (make-s arg1 arg2)
(match (list arg1 arg2)
((('K gg) ('K hh)) (=> fail)
(if (normalform? (list gg hh))
`(K (,gg ,hh))
(fail)))
((('delay ('K gg)) ('K hh)) (=> fail)
(if (and (normalform? hh) (not (contains-free-variables? hh)))
`(delay (K (,gg ,hh)))
(fail)))
((('K gg) 'V) (=> fail)
(if (normalform? (list gg 'V))
`(K (,gg V))
(fail)))
((('K gg) 'I) gg)
((('delay ('K gg)) 'I) `(delay ,gg))
((gg hh) `((S ,gg) ,hh))))
(define (eliminate-abstruction var body)
(cond ((eq? var body)
'I)
((or (atom? body)
(pass-through? body))
(list 'K body))
((eq? (car body) 'lambda)
(eliminate-abstruction var (eliminate-lambda body)))
((and (not (bound-in? var body))
(not (contains-free-variables? body)))
(let ((body (eliminate-lambda body)))
(if (normalform? body)
(list 'K body)
`(delay (K ,body)))))
(else
(let ((g (car body))
(h (cadr body)))
(if (eq? g 'delay)
(list 'K body)
(make-s (eliminate-abstruction var g)
(eliminate-abstruction var h)))))))
(define (normalform? e)
(match e
(('K x) (normalform? x))
(('S f) (normalform? f))
((('S f) g) (and (normalform? f) (normalform? g)))
(('delay x) #t)
(('unsafe x) #t)
(('? x) #t)
(- (atom? e))))
(define (eliminate-lambda x)
(cond ((or (atom? x) (pass-through? x))
x)
((eq? (car x) 'lambda)
(eliminate-abstruction (caadr x) (caddr x)))
(else
(list (eliminate-lambda (car x)) (eliminate-lambda (cadr x))))))
(define (bound-in? a x)
(cond ((atom? x) (eq? x a))
((pass-through? x) #f)
((eq? (car x) 'lambda)
(if (eq? (caadr x) a)
#f
(bound-in? a (caddr x))))
(else (or (bound-in? a (car x)) (bound-in? a (cadr x))))))
(define (closed? e env)
(cond ((pass-through? e) #t)
((atom? e) (memq e env))
((eq? (car e) 'lambda)
(let ((vars (cadr e))
(body (caddr e)))
(closed? body (append vars env))))
(else (and (closed? (car e) env)
(closed? (cadr e) env)))))
(define (contains-free-variables? x)
(not (closed? x '())))
(define (pass-through? x)
(if (pair? x)
(eq? (car x) '?)
(or (memq x '(I K V delay S call/cc unsafe @ !))
(char? x))))
(define (optimize-ski e)
(if (pair? e)
(let ((f (optimize-ski (car e)))
(x (optimize-ski (cadr e))))
(cond ((and (eq? f 'K)
(eq? x 'V))
'V) ; (K V) => V
((and (not (eq? f 'delay))
(pair? x)
(or (eq? (car x) '@)
(eq? (car x) '!))
(eq? (cadr x) 'I))
(list (car x) f)) ; (x ([@!] I)) => ([@!] x)
(else
(list f x))))
e))
(define (unlambdify x)
(match x
('I #\i)
('K #\k)
('S #\s)
('delay #\d)
('V #\v)
('@ #\@)
('! #\|)
(('? c) (list #\? c))
(('unsafe x) (unlambdify x))
('call/cc #\c)
('exit #\e)
((f a) (list #\` (unlambdify f) (unlambdify a)))
(#\newline #\r)
(-
(cond ((char? x) (list #\. x))
((string? x) x)
(else (error "unlambdify" "illegal unlambda" x))))))
(define (optimize-curried x)
(cond ((or (atom? x) (pass-through? x))
x)
((eq? (car x) 'lambda) ;(lambda (a) (lambda (b) a)) -> K
(let ((a (caadr x))
(b (caddr x)))
(if (and (pair? b)
(eq? (car b) 'lambda)
(not (eq? (caadr b) a))
(eq? (caddr b) a))
'K
`(lambda (,a) ,(optimize-curried b)))))
(else
(list (optimize-curried (car x)) (optimize-curried (cadr x))))))
(define (curry x)
(cond ((atom? x)
x)
((eq? (car x) 'lambda)
(let ((a (cadr x))
(b (caddr x)))
(cond ((null? a)
`(lambda (**dummy**) ,(curry b)))
((null? (cdr a))
`(lambda ,a ,(curry b)))
(else
`(lambda (,(car a)) ,(curry `(lambda ,(cdr a) ,b)))))))
(else
(fold (lambda (ei e) (if e (list e ei) ei))
#f (map curry x)))))
(define curried
(compose optimize-curried
curry
eliminate-lambda-rec))
(define compile
(compose optimize-ski eliminate-lambda curried))
(define (lambda->unlambda x)
(unlambdify (compile x)))
(define (eliminate-names macros names)
(filter (lambda (macro) (not (memq (car macro) names))) macros))
(define (macroexpand-arg arg)
(lambda (arg-args)
(if (null? arg-args)
arg
(cons arg arg-args))))
(define (make-macros args arg-names)
(if (or (null? args) (null? arg-names))
(values '() args arg-names)
(receive (macros rest-args rest-arg-names)
(make-macros (cdr args) (cdr arg-names))
(values (acons (car arg-names) (macroexpand-arg (car args)) macros)
rest-args rest-arg-names))))
(define (macroexpand-application arg-names body macros)
(lambda (args)
(receive (arg-macros args arg-names) (make-macros args arg-names)
(let ((macros (append arg-macros macros)))
(cond ((and (null? args) (null? arg-names))
(macroexpand macros body))
((null? args)
(macroexpand macros `(lambda ,arg-names ,body)))
((null? arg-names)
(cons (macroexpand macros body) args))
(else
(error "macroexpand-application" "make-macros does not work" (cons args arg-names))))))))
;; a macro is a (name . (lambda (macro-args) *body*))
(define (macroexpand macros expr)
(match expr
(('lambda args body)
`(lambda ,args ,(macroexpand (eliminate-names macros args) body)))
(('lambda-rec name args body)
`(lambda-rec ,name ,args ,(macroexpand (eliminate-names macros (cons name args)) body)))
((func . args)
(let ((macro (and (atom? func) (assq func macros))))
(if macro
((cdr macro) (map (lambda (arg) (macroexpand macros arg)) args))
(cons (macroexpand macros func) (map (lambda (arg) (macroexpand macros arg)) args)))))
(-
(let ((macro (assq expr macros)))
(if macro
((cdr macro) '())
expr)))))
(define (make-syntax name arg-names body macros)
(let ((cl (eval `(letrec ((,name (lambda ,arg-names ,body))) ,name)
(interaction-environment))))
(lambda (args)
(macroexpand macros (apply cl args)))))
(define unl-macros '())
(define (add-unl-macro! name args body)
; (print name args body)
(if (assq name unl-macros)
(error "redefined " name))
(set! unl-macros
(acons name
(macroexpand-application args body unl-macros)
unl-macros)))
(define (add-unl-syntax! name f)
(if (assq name unl-macros)
(error "redefined " name))
(set!
unl-macros
(acons name
(lambda (args) (macroexpand unl-macros (apply f args)))
unl-macros)))
(define-macro (defmacro name-args body)
(let ((name (if (pair? name-args) (car name-args) name-args))
(args (if (pair? name-args) (cdr name-args) '())))
(add-unl-macro! name args body))
#t)
(define-macro (defrecmacro name-args body)
(let ((name (if (pair? name-args) (car name-args) name-args))
(args (if (pair? name-args) (cdr name-args) '())))
(add-unl-macro! name '() `(lambda-rec ,name ,args ,body)))
#t)
(define-macro (defsyntax name-args body)
(if (assq (car name-args) unl-macros)
(error "redefined " name))
(set!
unl-macros
(acons (car name-args)
(make-syntax (car name-args) (cdr name-args) body unl-macros)
unl-macros))
#t)
(define (print-as-unl expr :optional (port (current-output-port)))
(write-tree (lambda->unlambda (macroexpand unl-macros expr)) port))
(define (compile-to-string expr)
(tree->string (lambda->unlambda (macroexpand unl-macros expr))))
(define (compile-to-file file expr)
(let ((expanded (macroexpand unl-macros expr))
(obj (file->sexp-list file :if-does-not-exist #f)))
(if (and obj (equal? (car obj) expanded))
(cadr obj)
(let ((compiled (tree->string (lambda->unlambda expanded))))
(call-with-output-file file
(lambda (port)
(write expanded port)
(write compiled port)))
compiled))))