NOTES revision 1590 
1234852Sbaptm4 - macro processor
2234852Sbapt
3234852SbaptPD m4 is based on the macro tool distributed with the software 
4234852Sbapttools (VOS) package, and described in the "SOFTWARE TOOLS" and 
5234852Sbapt"SOFTWARE TOOLS IN PASCAL" books. It has been expanded to include 
6234852Sbaptmost of the command set of SysV m4, the standard UN*X macro processor.
7234852Sbapt
8234852SbaptSince both PD m4 and UN*X m4 are based on SOFTWARE TOOLS macro,
9234852Sbaptthere may be certain implementation similarities between
10234852Sbaptthe two. The PD m4 was produced without ANY references to m4
11234852Sbaptsources.
12234852Sbapt
13234852Sbaptwritten by: Ozan S. Yigit
14234852Sbapt
15234852SbaptReferences:
16234852Sbapt
17234852Sbapt	Software Tools distribution: macro
18234852Sbapt
19234852Sbapt	Kernighan, Brian W. and P. J. Plauger, SOFTWARE
20234852Sbapt	TOOLS IN PASCAL, Addison-Wesley, Mass. 1981
21234852Sbapt
22234852Sbapt	Kernighan, Brian W. and P. J. Plauger, SOFTWARE
23234852Sbapt	TOOLS, Addison-Wesley, Mass. 1976
24234852Sbapt
25234852Sbapt	Kernighan, Brian W. and Dennis M. Ritchie,
26234852Sbapt	THE M4 MACRO PROCESSOR, Unix Programmer's Manual,
27234852Sbapt	Seventh Edition, Vol. 2, Bell Telephone Labs, 1979
28234852Sbapt
29234852Sbapt	System V man page for M4
30234852Sbapt
31234852Sbapt
32234852SbaptImplementation Notes:
33234852Sbapt
34234852Sbapt[1]	PD m4 uses a different (and simpler) stack mechanism than the one 
35234852Sbapt	described in Software Tools and Software Tools in Pascal books. 
36234852Sbapt	The triple stack thing is replaced with a single stack containing 
37234852Sbapt	the call frames and the arguments. Each frame is back-linked to a 
38234852Sbapt	previous stack frame, which enables us to rewind the stack after 
39234852Sbapt	each nested call is completed. Each argument is a character pointer 
40234852Sbapt	to the beginning of the argument string within the string space.
41234852Sbapt	The only exceptions to this are (*) arg 0 and arg 1, which are
42234852Sbapt	the macro definition and macro name strings, stored dynamically
43234852Sbapt	for the hash table.
44234852Sbapt
45234852Sbapt	    .					   .
46234852Sbapt	|   .	|  <-- sp			|  .  |
47234852Sbapt	+-------+				+-----+
48234852Sbapt	| arg 3 ------------------------------->| str |
49234852Sbapt	+-------+				|  .  |
50	| arg 2 --------------+ 		   .
51	+-------+	      |
52	    *		      |			|     |
53	+-------+	      | 		+-----+
54	| plev	|  <-- fp     +---------------->| str |
55	+-------+				|  .  |
56	| type	|				   .
57	+-------+
58	| prcf	-----------+		plev: paren level
59	+-------+  	   |		type: call type
60	|   .	| 	   |		prcf: prev. call frame
61	    .	   	   |
62	+-------+	   |
63	|	<----------+
64	+-------+
65