try to avoid races again (cf. 8c37cb84065f and fd3a36e48b09);
(* ML-Yacc Parser Generator (c) 1989 Andrew W. Appel, David R. Tarditi *)
(* Stream: a structure implementing a lazy stream. The signature STREAM
is found in base.sig *)
structure Stream :> STREAM =
struct
datatype 'a str = EVAL of 'a * 'a str ref | UNEVAL of (unit->'a)
type 'a stream = 'a str ref
fun get(ref(EVAL t)) = t
| get(s as ref(UNEVAL f)) =
let val t = (f(), ref(UNEVAL f)) in s := EVAL t; t end
fun streamify f = ref(UNEVAL f)
fun cons(a,s) = ref(EVAL(a,s))
end;