ref: 518415febfea39229bf8a23ad2435009a8c88147
dir: femtolisp/tests/ast/asttools.lsp
; -*- scheme -*-
; utilities for AST processing
(define (symconcat s1 s2)
(symbol (string s1 s2)))
(define (list-adjoin item lst)
(if (member item lst)
lst
(cons item lst)))
(define (index-of item lst start)
(cond ((null? lst) #f)
((eq item (car lst)) start)
(#t (index-of item (cdr lst) (+ start 1)))))
(define (each f l)
(if (null? l) l
(begin (f (car l))
(each f (cdr l)))))
(define (maptree-pre f tr)
(let ((new-t (f tr)))
(if (pair? new-t)
(map (lambda (e) (maptree-pre f e)) new-t)
new-t)))
(define (maptree-post f tr)
(if (not (pair? tr))
(f tr)
(let ((new-t (map (lambda (e) (maptree-post f e)) tr)))
(f new-t))))
(define (foldtree-pre f t zero)
(if (not (pair? t))
(f t zero)
(foldl t (lambda (e state) (foldtree-pre f e state)) (f t zero))))
(define (foldtree-post f t zero)
(if (not (pair? t))
(f t zero)
(f t (foldl t (lambda (e state) (foldtree-post f e state)) zero))))
; general tree transformer
; folds in preorder (foldtree-pre), maps in postorder (maptree-post)
; therefore state changes occur immediately, just by looking at the current node,
; while transformation follows evaluation order. this seems to be the most natural
; approach.
; (mapper tree state) - should return transformed tree given current state
; (folder tree state) - should return new state
(define (map&fold t zero mapper folder)
(let ((head (and (pair? t) (car t))))
(cond ((eq? head 'quote)
t)
((or (eq? head 'the) (eq? head 'meta))
(list head
(cadr t)
(map&fold (caddr t) zero mapper folder)))
(else
(let ((new-s (folder t zero)))
(mapper
(if (pair? t)
; head symbol is a tag; never transform it
(cons (car t)
(map (lambda (e) (map&fold e new-s mapper folder))
(cdr t)))
t)
new-s))))))
; convert to proper list, i.e. remove "dots", and append
(define (append.2 l tail)
(cond ((null? l) tail)
((atom? l) (cons l tail))
(#t (cons (car l) (append.2 (cdr l) tail)))))
; transform code by calling (f expr env) on each subexpr, where
; env is a list of lexical variables in effect at that point.
(define (lexical-walk f t)
(map&fold t () f
(lambda (tree state)
(if (and (eq? (car t) 'lambda)
(pair? (cdr t)))
(append.2 (cadr t) state)
state))))
; collapse forms like (&& (&& (&& (&& a b) c) d) e) to (&& a b c d e)
(define (flatten-left-op op e)
(maptree-post (lambda (node)
(if (and (pair? node)
(eq (car node) op)
(pair? (cdr node))
(pair? (cadr node))
(eq (caadr node) op))
(cons op
(append (cdadr node) (cddr node)))
node))
e))
; convert all local variable references to (lexref rib slot name)
; where rib is the nesting level and slot is the stack slot#
; name is just there for reference
; this assumes lambda is the only remaining naming form
(define (lookup-var v env lev)
(if (null? env) v
(let ((i (index-of v (car env) 0)))
(if i (list 'lexref lev i v)
(lookup-var v (cdr env) (+ lev 1))))))
(define (lvc- e env)
(cond ((symbol? e) (lookup-var e env 0))
((pair? e)
(if (eq (car e) 'quote)
e
(let* ((newvs (and (eq (car e) 'lambda) (cadr e)))
(newenv (if newvs (cons newvs env) env)))
(if newvs
(cons 'lambda
(cons (cadr e)
(map (lambda (se) (lvc- se newenv))
(cddr e))))
(map (lambda (se) (lvc- se env)) e)))))
(#t e)))
(define (lexical-var-conversion e)
(lvc- e ()))
; convert let to lambda
(define (let-expand e)
(maptree-post (lambda (n)
(if (and (pair? n) (eq (car n) 'let))
`((lambda ,(map car (cadr n)) ,@(cddr n))
,@(map cadr (cadr n)))
n))
e))
; alpha renaming
; transl is an assoc list ((old-sym-name . new-sym-name) ...)
(define (alpha-rename e transl)
(map&fold e
()
; mapper: replace symbol if unbound
(lambda (t env)
(if (symbol? t)
(let ((found (assq t transl)))
(if (and found
(not (memq t env)))
(cdr found)
t))
t))
; folder: add locals to environment if entering a new scope
(lambda (t env)
(if (and (pair? t) (or (eq? (car t) 'let)
(eq? (car t) 'lambda)))
(append (cadr t) env)
env))))
; flatten op with any associativity
(define-macro (flatten-all-op op e)
`(pattern-expand
(pattern-lambda (,op (-- l ...) (-- inner (,op ...)) (-- r ...))
(cons ',op (append l (cdr inner) r)))
,e))
(define-macro (pattern-lambda pat body)
(let* ((args (patargs pat))
(expander `(lambda ,args ,body)))
`(lambda (expr)
(let ((m (match ',pat expr)))
(if m
; matches; perform expansion
(apply ,expander (map (lambda (var) (cdr (or (assq var m) '(0 . #f))))
',args))
#f)))))