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#!r6rs
(library (aps list-utils)
(export range enumerate zip transpose distinct? let+ perm list-of-aux list-for
remove-dupl append-unique fold flatten list-of normalize symbol-table)
(import (rnrs) (sweet-macros) (aps cut) (for (aps lang) expand))
;;; macros
;;LET+
(def-syntax let+
(syntax-match ()
(sub (let+ expr)
#'expr)
(sub (let+ (() lst) expr)
#'(if (null? lst) expr
(apply error 'let+ "Too many elements" lst)))
(sub (let+ ((arg1 arg2 ... . rest) lst) expr)
#'(let ((ls lst))
(if (null? ls)
(apply error 'let+ "Missing arguments" '(arg1 arg2 ...))
(let+ (arg1 (car ls))
(let+ ((arg2 ... . rest) (cdr ls)) expr)))))
(sub (let+ (name value) expr)
#'(let ((name value)) expr)
(identifier? #'name)
(syntax-violation 'let+ "Argument is not an identifier" #'name))
(sub (let+ (name value) (n v) ... expr)
#'(let+ (name value) (let+ (n v) ... expr)))
))
;;END
;;LIST-OF
(def-syntax list-of-aux
(syntax-match (in is)
(sub (list-of-aux expr acc)
#'(cons expr acc))
(sub (list-of-aux expr acc (var in lst) rest ...)
#'(let loop ((ls lst))
(if (null? ls) acc
(let+ (var (car ls))
(list-of-aux expr (loop (cdr ls)) rest ...)))))
(sub (list-of-aux expr acc (var is exp) rest ...)
#'(let+ (var exp) (list-of-aux expr acc rest ...)))
(sub (list-of-aux expr acc pred? rest ...)
#'(if pred? (list-of-aux expr acc rest ...) acc))
))
(def-syntax (list-of expr rest ...)
#'(list-of-aux expr '() rest ...))
;;END
(def-syntax (list-for decl ... expr)
#'(list-of-aux expr '() decl ...))
;;SYMBOL-TABLE
(def-syntax (symbol-table arg ...)
(: with-syntax
((name value) ...)
(map (syntax-match ()
(sub n #'(n n) (identifier? #'n))
(sub (n v) #'(n v) (identifier? #'n)))
#'(arg ...))
#'(letrec ((name value) ...)
(list (list 'name name) ...))))
;;END
;;; utilities
;;RANGE
(define range
(case-lambda
((n) (range 0 n 1))
((n0 n)
(range n0 n 1))
((n0 n s)
(begin
(assert (and (for-all number? (list n0 n s)) (not (zero? s))))
(let ((cmp (if (> s 0) >= <=)))
(let loop ((i n0) (acc '()))
(if (cmp i n) (reverse acc)
(loop (+ i s) (cons i acc)))))))))
;;END
;;ZIP
(define (zip . lists)
(assert (for-all list? lists))
(apply map list lists))
;;END
;;TRANSPOSE
(define (transpose llist)
(if (and (list? llist) (for-all list? llist))
(apply map list llist)
(error 'transpose "not a list of lists" llist)))
;;END
;;ENUMERATE
(define (enumerate lst)
(zip (range (length lst)) lst))
;;END
;;DISTINCT?
;; check if the elements of a list are distinct according to eq?
(define (distinct? eq? items)
(if (null? items) #t ; no items
(let+ ((first . rest) items)
(cond
((null? rest) #t); single item
((exists (cut eq? first <>) rest) #f); duplicate
(else (distinct? eq? rest)); look at the sublist
))))
;;END
;;REMOVE-DUPL
;; ex: (remove-dupl = '(1 2 3 1 5 2 4)) => (1 2 3 5 4)
(define (remove-dupl eq? lst)
(reverse
(fold-left
(lambda (acc el)
(if (exists (cut eq? <> el) acc); duplicate
acc
(cons el acc)))
'() lst)))
;;END
;;APPEND-UNIQUE
;; ex: (append-unique = '(1 2 3) '(1 5 2 4)) => (1 2 3 5 4)
(define (append-unique eq? . lists)
(remove-dupl eq? (apply append lists)))
;;END
;;FOLD
(def-syntax fold
(syntax-match (left right in)
(sub (fold left (acc seed) (x in lst) (x* in lst*) ... new-acc)
(: with-syntax (a a* ...) (generate-temporaries #'(x x* ...))
#'(fold-left
(lambda (acc a a* ...)
(let+ ((x x* ...) (list a a* ...)) new-acc))
seed lst lst* ...)))
(sub (fold right (acc seed) (x in lst) (x* in lst*) ... new-acc)
(: with-syntax (a a* ...) (generate-temporaries #'(x x* ...))
#'(fold-right
(lambda (a a* ... acc)
(let+ ((x x* ...) (list a a* ...)) new-acc))
seed lst lst* ...)))
))
;;END
;;FLATTEN
(define (flatten lst)
(fold right (a '()) (x in lst)
(if (list? x) (append (flatten x) a) (cons x a))))
;;END
;;PERM
;; compute the permutations of a list of distinct elements
(define (perm eq? lst)
(cond
((null? lst) '()); empty list
((null? (cdr lst)) (list lst)); single element list
(else; multi-element list
(list-of (cons el ls)
(el in lst)
(ls in (perm eq? (remp (cut eq? el <>) lst)))))))
;;END
;;NORMALIZE
(define (normalize ls)
(map (syntax-match ()
(sub n #'(n n) (identifier? #'n))
(sub (n v) #'(n v) (identifier? #'n)))
ls))
;;END
)
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