.th M6 VI 11/15/72
.sh NAME
m6 \*- general purpose macro processor
.sh SYNOPSIS
.bd m6
[
.bd \*-d
arg1 ] [ arg2 [ arg3 ] ]
.sh DESCRIPTION
.it M6
takes input from file arg2 (or standard input if arg2 is missing)
and places output on file arg3 (or standard output).
A working file of definitions, ``m.def'',
is initialized from  file arg1 if that is supplied.
.it M6
differs from the standard [1] in these
respects:
.s3
#trace:, #source: and #end:
are not defined.
.s3
#meta,arg1,arg2: transfers the role of metacharacter
arg1 to character arg2. If two metacharacters become identical
thereby, the outcome of further processing is not guaranteed.
For example, to make [ ]{} play the
roles of #:<> type
.s3
.in+5
\\\#meta,<\\\#>,[:
.br
[meta,<:>,]:
.br
[meta,[substr,<<>>,1,1;,{]
.br
[meta,[substr,{{>>,2,1;,}]
.in-5
.s3
#del,arg1: deletes the definition of macro arg1.
.s3
#save: and #rest: save and restore the definition table together with
the current metacharacters on file
m.def.
.s3
#def,arg1,arg2,arg3: works as in the standard with the extension
that an integer may be
supplied to arg3 to cause the new macro to perform the
action of a specified builtin before its replacement text is evaluated.
Thus all builtins
except #def: can be retrieved even after deletion.
Codes for arg3 are:
.s3
.in+5
.nf
0 \*- no function
1,2,3,4,5,6 \*- gt,eq,ge,lt,ne,le
7,8 \*- seq,sne
9,10,11,12,13 \*- add,sub,mpy,div,exp
20 \*- if
21,22 \*- def,copy
23 \*- meta
24 \*- size
25 \*- substr
26,27 \*- go,gobk
28 \*- del
29 \*- dnl
30,31 \*- save,rest
.fi
.in-5
.sh FILES
m.def	working file of definitions
.br
/usr/lang/mdir/m6a	m6 processor proper (/usr/bin/m6 is only an initializer)
.br
/usr/lang/mdir/m6b	default initialization for m.def
.br
/bin/cp	used for copying initial value of m.def
.sh "SEE ALSO"
[1] A. D. Hall,
The M6 Macroprocessor, Bell Telephone Laboratories, 1969
.sh DIAGNOSTICS
``err''
\*- a bug, an unknown builtin or a bad definition table
.br
``oprd''\*-can't open input or initial definitions
.br
``opwr''\*-can't open output
.br
``ova'' \*- overflow of nested arguments
.br
``ovc'' \*- overflow of calls
.br
``ovd'' \*- overflow of definitions
.br
``Try again'' \*- no process available for copying m.def
.sh AUTHOR
M. D. McIlroy
.sh BUGS
Characters in internal tables are stored
one per word.
They really should be packed to improve capacity.
For want of space (and because of unpacked formats) no file arguments
have been provided to #save: or #rest:,
and no check is made on the actual opening of file m.def.
Again to save space,
garbage collection makes calls on #save: and #rest: and so overwrites
m.def.
.s3
Since the program is written in the defunct language
B it is currently unavailable.
Expressions of interest may make a C version appear.
