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