Module Hashtbl
structure Hashtbl = struct ... end
Hash tables and hash functions.
Hash tables are hashed association tables, with in-place modification.
type ('a, 'b) t
The type of hash tables from type 'a to type 'b.
val create : int -> ('a, 'b) t
Hashtbl.create n creates a new, empty hash table, with
initial size n. For best results, n should be on the
order of the expected number of elements that will be in
the table. The table grows as needed, so n is just an
initial guess.
val clear : ('a, 'b) t -> unit
Empty a hash table.
val add : ('a, 'b) t -> 'a -> 'b -> unit
Hashtbl.add tbl x y adds a binding of
x to
y in table
tbl.
Previous bindings for
x are not removed, but simply
hidden. That is, after performing
Hashtbl.remove tbl x,
the previous binding for
x, if any, is restored.
(Same behavior as with association lists.)
val copy : ('a, 'b) t -> ('a, 'b) t
Return a copy of the given hashtable.
val find : ('a, 'b) t -> 'a -> 'b
Hashtbl.find tbl x returns the current binding of x in tbl,
or raises Not_found if no such binding exists.
val find_all : ('a, 'b) t -> 'a -> 'b list
Hashtbl.find_all tbl x returns the list of all data
associated with x in tbl.
The current binding is returned first, then the previous
bindings, in reverse order of introduction in the table.
val mem : ('a, 'b) t -> 'a -> bool
Hashtbl.mem tbl x checks if x is bound in tbl.
val remove : ('a, 'b) t -> 'a -> unit
Hashtbl.remove tbl x removes the current binding of x in tbl,
restoring the previous binding if it exists.
It does nothing if x is not bound in tbl.
val replace : ('a, 'b) t -> 'a -> 'b -> unit
Hashtbl.replace tbl x y replaces the current binding of
x
in
tbl by a binding of
x to
y. If
x is unbound in
tbl,
a binding of
x to
y is added to
tbl.
This is functionally equivalent to
Hashtbl.remove tbl x
followed by
Hashtbl.add tbl x y.
val iter : ('a -> 'b -> unit) -> ('a, 'b) t -> unit
Hashtbl.iter f tbl applies f to all bindings in table tbl.
f receives the key as first argument, and the associated value
as second argument. The order in which the bindings are passed to
f is unspecified. Each binding is presented exactly once
to f.
val fold : ('a -> 'b -> 'c -> 'c) -> ('a, 'b) t -> 'c -> 'c
Hashtbl.fold f tbl init computes
(f kN dN ... (f k1 d1 init)...),
where k1 ... kN are the keys of all bindings in tbl,
and d1 ... dN are the associated values.
The order in which the bindings are passed to
f is unspecified. Each binding is presented exactly once
to f.
val hash : 'a -> int
Hashtbl.hash x associates a positive integer to any value of
any type. It is guaranteed that
if x = y, then hash x = hash y.
Moreover, hash always terminates, even on cyclic
structures.
val hash_param : int -> int -> 'a -> int
Hashtbl.hash_param n m x computes a hash value for x, with the
same properties as for hash. The two extra parameters n and
m give more precise control over hashing. Hashing performs a
depth-first, right-to-left traversal of the structure x, stopping
after n meaningful nodes were encountered, or m nodes,
meaningful or not, were encountered. Meaningful nodes are: integers;
floating-point numbers; strings; characters; booleans; and constant
constructors. Larger values of m and n means that more
nodes are taken into account to compute the final hash
value, and therefore collisions are less likely to happen.
However, hashing takes longer. The parameters m and n
govern the tradeoff between accuracy and speed.