[hcoop/debian/mlton.git] / lib / mlyacc-lib / stream.sml

(* 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;
Commit	Line	Data
7f918cf1 CE	1	(* ML-Yacc Parser Generator (c) 1989 Andrew W. Appel, David R. Tarditi *)
	2
	3	(* Stream: a structure implementing a lazy stream. The signature STREAM
	4	is found in base.sig *)
	5
	6	structure Stream :> STREAM =
	7	struct
	8	datatype 'a str = EVAL of 'a * 'a str ref \| UNEVAL of (unit->'a)
	9
	10	type 'a stream = 'a str ref
	11
	12	fun get(ref(EVAL t)) = t
	13	\| get(s as ref(UNEVAL f)) =
	14	let val t = (f(), ref(UNEVAL f)) in s := EVAL t; t end
	15
	16	fun streamify f = ref(UNEVAL f)
	17	fun cons(a,s) = ref(EVAL(a,s))
	18
	19	end;