pumana.n

早期freebsd实现

Notes on the listings
.PP
The first page of a listing
includes a banner line indicating the version and date of generation of
.PI
or
.PC .
It also
includes the
.UX
path name supplied for the source file and the date of
last modification of that file.
.PP
Within the body of the listing, lines are numbered consecutively and
correspond to the line numbers for the editor.
Currently, two special
kinds of lines may be used to format the listing:
a line consisting of a form-feed
character, control-l, which causes a page
eject in the listing, and a line with
no characters which causes the line number to be suppressed in the listing,
creating a truly blank line.
These lines thus correspond to `eject' and `space' macros found in many
assemblers.
Non-printing characters are printed as the character `?' in the listing.\*(dg
.FS
\*(dgThe character generated by a control-i indents
to the next `tab stop'.
Tab stops are set every 8 columns in
.UX .
Tabs thus provide a quick way of indenting in the program.
.FE
.SH
The standard procedure write
.PP
If no minimum field length parameter is specified
for a
.I write,
the following default
values are assumed:
.KS
.TS
center;
l n.
integer	10
real	22
Boolean	length of `true' or `false'
char	1
string	length of the string
oct	11
hex	8
.TE
.KE
The end of each line in a text file should be explicitly
indicated by `writeln(f)', where `writeln(output)' may be written
simply as `writeln'.
For
.UX ,
the built-in function `page(f)' puts a single
.SM ASCII
form-feed character on the output file.
For programs which are to be transported the filter
.I pcc
can be used to interpret carriage control, as
.UX
does not normally do so.
.NH 2
Restrictions and limitations
.SH
Files
.PP
Files cannot be members of files or members of dynamically
allocated structures.
.SH
Arrays, sets and strings
.PP
The calculations involving array subscripts and set elements
are done with 16 bit arithmetic.
This
restricts the types over which arrays and sets may be defined.
The lower bound of such a range must be greater than or equal to
\-32768, and the upper bound less than 32768.
In particular, strings may have any length from 1 to 65535 characters,
and sets may contain no more than 65535 elements.
.SH
Line and symbol length
.PP
There is no intrinsic limit on the length of identifiers.
Identifiers
are considered to be distinct if they differ
in any single position over their entire length.
There is a limit, however, on the maximum input
line length.
This limit is quite generous however, currently exceeding 160
characters.
.SH
Procedure and function nesting and program size
.PP
At most 20 levels of 
.B procedure 
and 
.B function 
nesting are allowed.
There is no fundamental, translator defined limit on the size of the
program which can be translated.
The ultimate limit is supplied by the
hardware and thus, on the \s-2PDP\s0-11,
by the 16 bit address space.
If
one runs up against the `ran out of memory' diagnostic the program may yet
translate if smaller procedures are used, as a lot of space is freed
by the translator at the completion of each 
.B procedure
or
.B function
in the current
implementation.
.PP
On the \s-2VAX\s0-11, there is an implementation defined limit
of 65536 bytes per variable.
There is no limit on the number of variables.
.SH
Overflow
.PP
There is currently no checking for overflow on arithmetic operations at
run-time on the \s-2PDP\s0-11.
Overflow checking is performed on the \s-2VAX\s0-11 by the hardware.
.br
.ne 15
.NH 2
Added types, operators, procedures and functions
.SH
Additional predefined types
.PP
The type
.I alfa
is predefined as:
.LS
\*btype\fP alfa = \*bpacked\fP \*barray\fP [ 1..10 ] \*bof\fP \*bchar\fP
.LE
.PP
The type
.I intset
is predefined as:
.LS
\*btype\fP intset = \*bset of\fP 0..127
.LE
In most cases the context of an expression involving a constant
set allows the translator to determine the type of the set, even though the
constant set itself may not uniquely determine this type.
In the
cases where it is not possible to determine the type of the set from
local context, the expression type defaults to a set over the entire base
type unless the base type is integer\*(dg.
.FS
\*(dgThe current translator makes a special case of the construct
`if ... in [ ... ]' and enforces only the more lax restriction
on 16 bit arithmetic given above in this case.
.FE
In the latter case the type defaults to the current
binding of
.I intset,
which must be ``type set of (a subrange of) integer'' at that point.
.PP
Note that if 
.I intset 
is redefined via:
.LS
\*btype\fP intset = \*bset of\fP 0..58;
.LE
then the default integer set is the implicit
.I intset 
of
Pascal 6000\-3.4
.SH
Additional predefined operators
.PP
The relationals `<' and `>' of proper set
inclusion are available.
With
.I a
and
.I b
sets, note that
.LS
(\*bnot\fR (\fIa\fR < \fIb\fR)) <> (\fIa\fR >= \fIb\fR)
.LE
As an example consider the sets
.I a
= [0,2]
and
.I b
= [1].
The only relation true between these sets is `<>'.
.SH
Non-standard procedures
.IP argv(i,a) 25
where
.I i 
is an integer and
.I a
is a string variable
assigns the (possibly truncated or blank padded)
.I i \|'th
argument
of the invocation of the current
.UX
process to the variable
.I a .
The range of valid
.I i
is
.I 0
to
.I argc\-1 .
.IP date(a) 
assigns the current date to the alfa variable 
.I a
in the format `dd mmm yy ', where `mmm' is the first
three characters of the month, i.e. `Apr'.
.IP flush(f) 
writes the output buffered for Pascal file
.I f
into the associated
.UX
file.
.IP halt 
terminates the execution of the program with
a control flow backtrace.
.IP linelimit(f,x)\*(dd
.FS
\*(ddCurrently ignored by pdp-11
.X .
.FE
with
.I f 
a textfile and
.I x 
an integer expression
causes
the program to be abnormally terminated if more than
.I x 
lines are
written on file
.I f .
If
.I x 
is less than 0 then no limit is imposed.
.IP message(x,...) 
causes the parameters, which have the format of those
to the
built-in
.B procedure
.I write,
to be written unbuffered on the diagnostic unit 2,
almost always the user's terminal.
.IP null
a procedure of no arguments which does absolutely nothing.
It is useful as a place holder,
and is generated by
.XP
in place of the invisible empty statement.
.IP remove(a) 
where
.I a 
is a string causes the
.UX
file whose
name is
.I a, 
with trailing blanks eliminated, to be removed.
.IP reset(f,a) 
where
.I a 
is a string causes the file whose name
is
.I a 
(with blanks trimmed) to be associated with
.I f 
in addition
to the normal function of
.I reset.
.IP rewrite(f,a) 
is analogous to `reset' above.
.IP stlimit(i)
where
.I i 
is an integer sets the statement limit to be
.I i 
statements.
Specifying the
.B p
option to
.I pc
disables statement limit counting.
.IP time(a) 
causes the current time in the form `\ hh:mm:ss\ ' to be
assigned to the alfa variable
.I a.
.SH
Non-standard functions
.IP argc 25
returns the count of arguments when the Pascal program
was invoked.
.I Argc
is always at least 1.
.IP card(x) 
returns the cardinality of the set
.I x, 
i.e. the
number of elements contained in the set.
.IP clock 
returns an integer which is the number of central processor
milliseconds of user time used by this process.
.IP expo(x) 
yields the integer valued exponent of the floating-point
representation of
.I x ;
expo(\fIx\fP) = entier(log2(abs(\fIx\fP))).
.IP random(x) 
where
.I x 
is a real parameter, evaluated but otherwise
ignored, invokes a linear congruential random number generator.
Successive seeds are generated as (seed*a + c) mod m and
the new random number is a normalization of the seed to the range 0.0 to 1.0;
a is 62605, c is 113218009, and m is
536870912.
The initial seed
is 7774755.
.IP seed(i) 
where
.I i 
is an integer sets the random number generator seed
to
.I i 
and returns the previous seed.
Thus seed(seed(i))
has no effect except to yield value
.I i.
.IP sysclock
an integer function of no arguments returns the number of central processor
milliseconds of system time used by this process.
.IP undefined(x) 
a Boolean function.
Its argument is a real number and
it always returns false.
.IP wallclock 
an integer function of no arguments returns the time
in seconds since 00:00:00 GMT January 1, 1970.
.NH 2
Remarks on standard and portable Pascal
.PP
It is occasionally desirable to prepare Pascal programs which will be
acceptable at other Pascal installations.
While certain system dependencies are bound to creep in,
judicious design and programming practice can usually eliminate
most of the non-portable usages.
Wirth's
.I "Pascal Report"
concludes with a standard for implementation and program exchange.
.PP
In particular, the following differences may cause trouble when attempting
to transport programs between this implementation and Pascal 6000\-3.4.
Using the
.B s
translator option may serve to indicate many problem areas.\*(dg
.FS
\*(dgThe
.B s
option does not, however, check that identifiers differ
in the first 8 characters.
.I Pi
and
.PC
also do not check the semantics of
.B packed .
.FE
.SH
Features not available in Berkeley Pascal
.IP
Segmented files and associated functions and procedures.
.IP
The function
.I trunc 
with two arguments.
.IP
Arrays whose indices exceed the capacity of 16 bit arithmetic.
.SH
Features available in Berkeley Pascal but not in Pascal 6000-3.4
.IP
The procedures
.I  reset 
and
.I  rewrite 
with file names.
.IP
The functions
.I argc,
.I seed,
.I sysclock,
and
.I wallclock.
.IP
The procedures
.I argv,
.I flush,
and
.I remove.
.IP
.I Message
with arguments other than character strings.
.IP
.I Write
with keyword
.B hex .
.IP
The
.B assert
statement.
.IP
Reading and writing of enumerated types.
.IP
Allowing functions to return structures.
.IP
Separate compilation of programs.
.IP
Comparison of records.
.SH
Other problem areas
.PP
Sets and strings are more general in \*
.UP ;
see the restrictions given in
the 
Jensen-Wirth
.I "User Manual"
for details on the 6000\-3.4 restrictions.
.PP
The character set differences may cause problems,
especially the use of the function
.I chr,
characters as arguments to
.I ord,
and comparisons of characters,
since the character set ordering
differs between the two machines.
.PP
The Pascal 6000\-3.4 compiler uses a less strict notion of type equivalence.
In
.UP ,
types are considered identical only if they are represented
by the same type identifier.
Thus, in particular, unnamed types are unique
to the variables/fields declared with them.
.PP
Pascal 6000\-3.4 doesn't recognize our option
flags, so it is wise to
put the control of
.UP
options to the end of option lists or, better
yet, restrict the option list length to one.
.PP
For Pascal 6000\-3.4 the ordering of files in the program statement has
significance.
It is desirable to place
.I input 
and
.I output 
as the first two files in the
.B program
statement.
.sp 2
.SH
Acknowledgments
.PP
The financial support of William Joy and Susan Graham by
the National Science Foundation under grants
MCS74-07644-A04, MCS78-07291, and MCS80-05144,
and the William Joy by an
.SM IBM
Graduate Fellowship are gratefully acknowledged.