TFL/utils.ML

tuned rewrite/simplify interface;

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−(*  Title:      TFL/utils.ML
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−    ID:         $Id$
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−    Author:     Konrad Slind, Cambridge University Computer Laboratory
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−    Copyright   1997  University of Cambridge
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−
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−Basic utilities.
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−*)
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−
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−signature UTILS =
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−sig
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−  exception ERR of {module: string, func: string, mesg: string}
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−  val C: ('a -> 'b -> 'c) -> 'b -> 'a -> 'c
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−  val itlist: ('a -> 'b -> 'b) -> 'a list -> 'b -> 'b
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−  val rev_itlist: ('a -> 'b -> 'b) -> 'a list -> 'b -> 'b
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−  val end_itlist: ('a -> 'a -> 'a) -> 'a list -> 'a
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−  val itlist2: ('a -> 'b -> 'c -> 'c) -> 'a list -> 'b list -> 'c -> 'c
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−  val pluck: ('a -> bool) -> 'a list -> 'a * 'a list
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−  val zip3: 'a list -> 'b list -> 'c list -> ('a*'b*'c) list
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−  val take: ('a -> 'b) -> int * 'a list -> 'b list
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−end;
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−
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−structure Utils: UTILS =
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−struct
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−
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−(*standard exception for TFL*)
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−exception ERR of {module: string, func: string, mesg: string};
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−
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−fun UTILS_ERR func mesg = ERR {module = "Utils", func = func, mesg = mesg};
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−
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−
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−fun C f x y = f y x
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−
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−fun itlist f L base_value =
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−   let fun it [] = base_value
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−         | it (a::rst) = f a (it rst)
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−   in it L
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−   end;
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−
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−fun rev_itlist f =
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−   let fun rev_it [] base = base
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−         | rev_it (a::rst) base = rev_it rst (f a base)
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−   in rev_it
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−   end;
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−
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−fun end_itlist f =
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−   let fun endit [] = raise UTILS_ERR "end_itlist" "list too short"
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−         | endit alist =
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−            let val (base::ralist) = rev alist
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−            in itlist f (rev ralist) base
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−            end
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−   in endit
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−   end;
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−
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−fun itlist2 f L1 L2 base_value =
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− let fun it ([],[]) = base_value
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−       | it ((a::rst1),(b::rst2)) = f a b (it (rst1,rst2))
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−       | it _ = raise UTILS_ERR "itlist2" "different length lists"
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− in  it (L1,L2)
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− end;
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−
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−fun pluck p  =
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−  let fun remv ([],_) = raise UTILS_ERR "pluck" "item not found"
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−        | remv (h::t, A) = if p h then (h, rev A @ t) else remv (t,h::A)
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−  in fn L => remv(L,[])
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−  end;
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−
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−fun take f =
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−  let fun grab(0,L) = []
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−        | grab(n, x::rst) = f x::grab(n-1,rst)
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−  in grab
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−  end;
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−
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−fun zip3 [][][] = []
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−  | zip3 (x::l1) (y::l2) (z::l3) = (x,y,z)::zip3 l1 l2 l3
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−  | zip3 _ _ _ = raise UTILS_ERR "zip3" "different lengths";
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−
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−
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−end;