Annotation of /sml/branches/SMLNJ/src/ml-yacc/lib/stream.sml

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1 :	monnier	2	(* ML-Yacc Parser Generator (c) 1989 Andrew W. Appel, David R. Tarditi
2 :			*
3 :			* $Log$
4 :	monnier	8	* Revision 1.1.1.2 1998/01/18 01:00:08 monnier
5 :			* *** empty log message ***
6 :	monnier	2	*
7 :	monnier	8	* Revision 1.2 1997/08/26 19:18:55 jhr
8 :			* Replaced used of "abstraction" with ":>".
9 :			*
10 :	monnier	2	# Revision 1.1.1.1 1997/01/14 01:38:04 george
11 :			# Version 109.24
12 :			#
13 :			* Revision 1.1.1.1 1996/01/31 16:01:43 george
14 :			* Version 109
15 :			*
16 :			*)
17 :
18 :			(* Stream: a structure implementing a lazy stream. The signature STREAM
19 :			is found in base.sig *)
20 :
21 :			structure Stream :> STREAM =
22 :			struct
23 :			datatype 'a str = EVAL of 'a * 'a str ref | UNEVAL of (unit->'a)
24 :
25 :			type 'a stream = 'a str ref
26 :
27 :			fun get(ref(EVAL t)) = t
28 :			| get(s as ref(UNEVAL f)) =
29 :			let val t = (f(), ref(UNEVAL f)) in s := EVAL t; t end
30 :
31 :			fun streamify f = ref(UNEVAL f)
32 :			fun cons(a,s) = ref(EVAL(a,s))
33 :
34 :			end;

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