author | wenzelm |
Thu, 24 Jan 2008 23:51:15 +0100 | |
changeset 25955 | 94a515ed8a39 |
parent 23178 | 07ba6b58b3d2 |
child 26887 | 0ae304689d01 |
permissions | -rw-r--r-- |
6118 | 1 |
(* Title: Pure/General/seq.ML |
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ID: $Id$ |
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Author: Lawrence C Paulson, Cambridge University Computer Laboratory |
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Author: Markus Wenzel, TU Munich |
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Unbounded sequences implemented by closures. RECOMPUTES if sequence |
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is re-inspected. Memoing, using polymorphic refs, was found to be |
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slower! (More GCs) |
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*) |
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signature SEQ = |
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sig |
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type 'a seq |
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val make: (unit -> ('a * 'a seq) option) -> 'a seq |
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val pull: 'a seq -> ('a * 'a seq) option |
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val empty: 'a seq |
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val cons: 'a -> 'a seq -> 'a seq |
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val single: 'a -> 'a seq |
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val try: ('a -> 'b) -> 'a -> 'b seq |
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val hd: 'a seq -> 'a |
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val tl: 'a seq -> 'a seq |
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val chop: int -> 'a seq -> 'a list * 'a seq |
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val list_of: 'a seq -> 'a list |
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val of_list: 'a list -> 'a seq |
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val append: 'a seq -> 'a seq -> 'a seq |
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val mapp: ('a -> 'b) -> 'a seq -> 'b seq -> 'b seq |
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val interleave: 'a seq * 'a seq -> 'a seq |
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val filter: ('a -> bool) -> 'a seq -> 'a seq |
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val flat: 'a seq seq -> 'a seq |
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val map: ('a -> 'b) -> 'a seq -> 'b seq |
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val maps: ('a -> 'b seq) -> 'a seq -> 'b seq |
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val map_filter: ('a -> 'b option) -> 'a seq -> 'b seq |
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val lift: ('a -> 'b -> 'c) -> 'a seq -> 'b -> 'c seq |
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val lifts: ('a -> 'b -> 'c seq) -> 'a seq -> 'b -> 'c seq |
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val singleton: ('a list -> 'b list seq) -> 'a -> 'b seq |
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val wrap: ((unit -> ('a * 'a seq) option) -> ('a * 'a seq) option) -> 'a seq -> 'a seq |
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val print: (int -> 'a -> unit) -> int -> 'a seq -> unit |
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val it_right : ('a * 'b seq -> 'b seq) -> 'a seq * 'b seq -> 'b seq |
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val succeed: 'a -> 'a seq |
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val fail: 'a -> 'b seq |
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val THEN: ('a -> 'b seq) * ('b -> 'c seq) -> 'a -> 'c seq |
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val ORELSE: ('a -> 'b seq) * ('a -> 'b seq) -> 'a -> 'b seq |
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val APPEND: ('a -> 'b seq) * ('a -> 'b seq) -> 'a -> 'b seq |
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val EVERY: ('a -> 'a seq) list -> 'a -> 'a seq |
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val FIRST: ('a -> 'b seq) list -> 'a -> 'b seq |
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val TRY: ('a -> 'a seq) -> 'a -> 'a seq |
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val REPEAT: ('a -> 'a seq) -> 'a -> 'a seq |
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val REPEAT1: ('a -> 'a seq) -> 'a -> 'a seq |
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val INTERVAL: (int -> 'a -> 'a seq) -> int -> int -> 'a -> 'a seq |
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val DETERM: ('a -> 'b seq) -> 'a -> 'b seq |
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end; |
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structure Seq: SEQ = |
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struct |
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(** lazy sequences **) |
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datatype 'a seq = Seq of unit -> ('a * 'a seq) option; |
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(*the abstraction for making a sequence*) |
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val make = Seq; |
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(*return next sequence element as NONE or SOME (x, xq)*) |
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fun pull (Seq f) = f (); |
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(*the empty sequence*) |
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val empty = Seq (fn () => NONE); |
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(*prefix an element to the sequence -- use cons (x, xq) only if |
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evaluation of xq need not be delayed, otherwise use |
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make (fn () => SOME (x, xq))*) |
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fun cons x xq = make (fn () => SOME (x, xq)); |
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fun single x = cons x empty; |
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(*head and tail -- beware of calling the sequence function twice!!*) |
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fun hd xq = #1 (the (pull xq)) |
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and tl xq = #2 (the (pull xq)); |
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(*partial function as procedure*) |
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fun try f x = |
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f34ac19659ae
moved some fundamental concepts to General/basics.ML;
wenzelm
parents:
21270
diff
changeset
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(case Basics.try f x of |
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SOME y => single y |
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| NONE => empty); |
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(*the list of the first n elements, paired with rest of sequence; |
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if length of list is less than n, then sequence had less than n elements*) |
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fun chop n xq = |
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if n <= 0 then ([], xq) |
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else |
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(case pull xq of |
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NONE => ([], xq) |
21395
f34ac19659ae
moved some fundamental concepts to General/basics.ML;
wenzelm
parents:
21270
diff
changeset
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| SOME (x, xq') => apfst (Basics.cons x) (chop (n - 1) xq')); |
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(*conversion from sequence to list*) |
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fun list_of xq = |
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(case pull xq of |
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NONE => [] |
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| SOME (x, xq') => x :: list_of xq'); |
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(*conversion from list to sequence*) |
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fun of_list xs = fold_rev cons xs empty; |
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(*sequence append: put the elements of xq in front of those of yq*) |
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fun append xq yq = |
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let |
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fun copy s = |
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make (fn () => |
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(case pull s of |
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NONE => pull yq |
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| SOME (x, s') => SOME (x, copy s'))) |
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in copy xq end; |
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(*map over a sequence xq, append the sequence yq*) |
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fun mapp f xq yq = |
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let |
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fun copy s = |
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make (fn () => |
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(case pull s of |
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NONE => pull yq |
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| SOME (x, s') => SOME (f x, copy s'))) |
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in copy xq end; |
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(*interleave elements of xq with those of yq -- fairer than append*) |
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fun interleave (xq, yq) = |
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make (fn () => |
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(case pull xq of |
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NONE => pull yq |
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| SOME (x, xq') => SOME (x, interleave (yq, xq')))); |
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(*filter sequence by predicate*) |
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fun filter pred xq = |
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let |
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fun copy s = |
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make (fn () => |
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(case pull s of |
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NONE => NONE |
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| SOME (x, s') => if pred x then SOME (x, copy s') else pull (copy s'))); |
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in copy xq end; |
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(*flatten a sequence of sequences to a single sequence*) |
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fun flat xqq = |
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make (fn () => |
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(case pull xqq of |
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NONE => NONE |
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| SOME (xq, xqq') => pull (append xq (flat xqq')))); |
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(*map the function f over the sequence, making a new sequence*) |
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fun map f xq = |
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make (fn () => |
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(case pull xq of |
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NONE => NONE |
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| SOME (x, xq') => SOME (f x, map f xq'))); |
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fun maps f = flat o map f; |
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fun map_filter f = maps (fn x => (case f x of NONE => empty | SOME y => single y)); |
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fun lift f xq y = map (fn x => f x y) xq; |
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fun lifts f xq y = maps (fn x => f x y) xq; |
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fun singleton f x = f [x] |> map (fn [y] => y | _ => raise Empty); |
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(*wrapped lazy evaluation*) |
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fun wrap f xq = |
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make (fn () => |
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(case f (fn () => pull xq) of |
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NONE => NONE |
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| SOME (x, xq') => SOME (x, wrap f xq'))); |
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(*print a sequence, up to "count" elements*) |
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fun print print_elem count = |
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let |
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fun prnt k xq = |
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if k > count then () |
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else |
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(case pull xq of |
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NONE => () |
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| SOME (x, xq') => (print_elem k x; writeln ""; prnt (k + 1) xq')); |
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in prnt 1 end; |
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(*accumulating a function over a sequence; this is lazy*) |
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fun it_right f (xq, yq) = |
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let |
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fun its s = |
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make (fn () => |
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(case pull s of |
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NONE => pull yq |
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| SOME (a, s') => pull (f (a, its s')))) |
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in its xq end; |
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(** sequence functions **) (*cf. Pure/tctical.ML*) |
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fun succeed x = single x; |
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fun fail _ = empty; |
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fun op THEN (f, g) x = maps g (f x); |
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fun op ORELSE (f, g) x = |
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(case pull (f x) of |
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NONE => g x |
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| some => make (fn () => some)); |
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fun op APPEND (f, g) x = |
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append (f x) (make (fn () => pull (g x))); |
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fun EVERY fs = fold_rev (curry op THEN) fs succeed; |
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fun FIRST fs = fold_rev (curry op ORELSE) fs fail; |
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fun TRY f = ORELSE (f, succeed); |
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fun REPEAT f = |
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let |
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fun rep qs x = |
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(case pull (f x) of |
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NONE => SOME (x, make (fn () => repq qs)) |
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| SOME (x', q) => rep (q :: qs) x') |
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and repq [] = NONE |
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| repq (q :: qs) = |
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(case pull q of |
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NONE => repq qs |
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| SOME (x, q) => rep (q :: qs) x); |
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in fn x => make (fn () => rep [] x) end; |
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fun REPEAT1 f = THEN (f, REPEAT f); |
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fun INTERVAL f i j x = |
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if i > j then single x |
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else op THEN (f j, INTERVAL f i (j - 1)) x; |
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fun DETERM f x = |
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(case pull (f x) of |
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NONE => empty |
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| SOME (x', _) => cons x' empty); |
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end; |