TFL/utils.ML
author ballarin
Wed Jul 19 19:25:58 2006 +0200 (2006-07-19)
changeset 20168 ed7bced29e1b
parent 16854 fdd362b7e980
permissions -rw-r--r--
Reimplemented algebra method; now controlled by attribute.
     1 (*  Title:      TFL/utils.ML
     2     ID:         $Id$
     3     Author:     Konrad Slind, Cambridge University Computer Laboratory
     4     Copyright   1997  University of Cambridge
     5 
     6 Basic utilities.
     7 *)
     8 
     9 signature UTILS =
    10 sig
    11   exception ERR of {module: string, func: string, mesg: string}
    12   val C: ('a -> 'b -> 'c) -> 'b -> 'a -> 'c
    13   val end_itlist: ('a -> 'a -> 'a) -> 'a list -> 'a
    14   val itlist2: ('a -> 'b -> 'c -> 'c) -> 'a list -> 'b list -> 'c -> 'c
    15   val pluck: ('a -> bool) -> 'a list -> 'a * 'a list
    16   val zip3: 'a list -> 'b list -> 'c list -> ('a*'b*'c) list
    17   val take: ('a -> 'b) -> int * 'a list -> 'b list
    18 end;
    19 
    20 structure Utils: UTILS =
    21 struct
    22 
    23 (*standard exception for TFL*)
    24 exception ERR of {module: string, func: string, mesg: string};
    25 
    26 fun UTILS_ERR func mesg = ERR {module = "Utils", func = func, mesg = mesg};
    27 
    28 
    29 fun C f x y = f y x
    30 
    31 fun end_itlist f [] = raise (UTILS_ERR "end_itlist" "list too short")
    32   | end_itlist f [x] = x 
    33   | end_itlist f (x :: xs) = f x (end_itlist f xs);
    34 
    35 fun itlist2 f L1 L2 base_value =
    36  let fun it ([],[]) = base_value
    37        | it ((a::rst1),(b::rst2)) = f a b (it (rst1,rst2))
    38        | it _ = raise UTILS_ERR "itlist2" "different length lists"
    39  in  it (L1,L2)
    40  end;
    41 
    42 fun pluck p  =
    43   let fun remv ([],_) = raise UTILS_ERR "pluck" "item not found"
    44         | remv (h::t, A) = if p h then (h, rev A @ t) else remv (t,h::A)
    45   in fn L => remv(L,[])
    46   end;
    47 
    48 fun take f =
    49   let fun grab(0,L) = []
    50         | grab(n, x::rst) = f x::grab(n-1,rst)
    51   in grab
    52   end;
    53 
    54 fun zip3 [][][] = []
    55   | zip3 (x::l1) (y::l2) (z::l3) = (x,y,z)::zip3 l1 l2 l3
    56   | zip3 _ _ _ = raise UTILS_ERR "zip3" "different lengths";
    57 
    58 
    59 end;