(* Title: TFL/utils.sml
ID: $Id$
Author: Konrad Slind, Cambridge University Computer Laboratory
Copyright 1997 University of Cambridge
Basic utilities.
*)
signature Utils_sig =
sig
exception ERR of {module:string,func:string, mesg:string}
val can : ('a -> 'b) -> 'a -> bool
val holds : ('a -> bool) -> 'a -> bool
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
val sort : ('a -> 'a -> bool) -> 'a list -> 'a list
end;
structure 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};
(* Simple combinators *)
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{func="end_itlist", mesg="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{func="itlist2",mesg="different length lists"}
in it (L1,L2)
end;
fun pluck p =
let fun remv ([],_) = raise UTILS_ERR{func="pluck",mesg = "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{func="zip3",mesg="different lengths"};
fun can f x = (f x ; true) handle _ => false; (* FIXME do not handle _ !!! *)
fun holds P x = P x handle _ => false; (* FIXME do not handle _ !!! *)
fun sort R =
let fun part (m, []) = ([],[])
| part (m, h::rst) =
let val (l1,l2) = part (m,rst)
in if (R h m) then (h::l1, l2)
else (l1, h::l2) end
fun qsort [] = []
| qsort (h::rst) =
let val (l1,l2) = part(h,rst)
in qsort l1@ [h] @qsort l2
end
in qsort
end;
end;