(*
 * This file contains definitions for a simple Lisp-like alist and associated
 * functions.  What's simple is that alist items are restricted to be
 * string*int tuples, which means that only int values can be stored in the
 * alist.  The example lispval.ml defines a more general form of Lisp data
 * value.  The alist definition in this file can be combined with the general
 * value definition to build alists that fully represent Lisp data and
 * bindings.
 *)
type binding = string * int;
type alist = binding list;

val nilAlist = ("", 0):binding;

fun bindingKey(b:binding):string = #1(b);
fun bindingVal(b:binding):int = #2(b);

fun assoc(key:string, al:alist):binding =
    if al = nil then nilAlist
    else if key = bindingKey(hd(al)) then hd(al)
    else assoc(key, tl(al));

(*
 * Simple tests of the alist functions.
 *)
val a = [("x",10),("y",20),("z",30)];
bindingVal(assoc("x", a));
bindingVal(assoc("z", a));
bindingVal(assoc("w", a));