pumana.n

早期freebsd实现

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.\"	@(#)pumanA.n	8.1 (Berkeley) 6/8/93
.\"
.if !\n(xx \{\
.so tmac.p \}
.ND
.nr H1 0
.af H1 A
.NH 
Appendix to Wirth's Pascal Report
.PP
This section is an appendix to
the definition of the Pascal language in Niklaus Wirth's
.I "Pascal Report"
and, with that Report, precisely defines the
Berkeley
implementation.
This appendix includes a summary of extensions to the language,
gives the ways in which the undefined specifications were resolved,
gives limitations and restrictions of the current implementation,
and lists the added functions and procedures available.
It concludes with a list of differences with the commonly available
Pascal 6000\-3.4 implementation,
and some comments on standard and portable Pascal.
.NH 2
Extensions to the language Pascal
.PP
This section defines non-standard language constructs available in
.UP .
The
.B s
standard Pascal option of the translators
.PI
and
.PC
can be used to detect these extensions in programs which are to be transported.
.SH
String padding
.PP
.UP
will pad constant strings with blanks in expressions and as
value parameters to make them as long as is required.
The following is a legal
.UP
program:
.LS
\*bprogram\fP x(output);
\*bvar\fP z : \*bpacked\fP \*barray\fP [ 1 .. 13 ] \*bof\fP char;
\*bbegin\fP
    z := 'red';
    writeln(z)
\*bend\fP;
.LE
The padded blanks are added on the right.
Thus the assignment above is equivalent to:
.LS
z := 'red          '
.LE
which is standard Pascal.
.SH
Octal constants, octal and hexadecimal write
.PP
Octal constants may be given as a sequence of octal digits followed
by the character `b' or `B'.
The forms
.LS
write(a:n \*boct\fP)
.LE
and
.LS
write(a:n \*bhex\fP)
.LE
cause the internal representation of
expression
.I a,
which must be Boolean, character, integer, pointer, or a user-defined enumerated
type,
to be written in octal or hexadecimal respectively.
.SH
Assert statement
.PP
An
.B assert
statement causes a
.I Boolean
expression to be evaluated
each time the statement is executed.
A runtime error results if any of the expressions evaluates to be 
.I false .
The
.B assert
statement is treated as a comment if run-time tests are disabled.
The syntax for
.B assert
is:
.LS
\*bassert\fP <expr>
.LE
.SH
Enumerated type input-output
.PP
Enumerated types may be read and written.
On output the string name associated with the enumerated
value is output.
If the value is out of range,
a runtime error occurs.
On input an identifier is read and looked up
in a table of names associated with the
type of the variable, and
the appropriate internal value is assigned to the variable being
read.
If the name is not found in the table
a runtime error occurs.
.SH
Structure returning functions
.PP
An extension has been added which allows functions 
to return arbitrary sized structures rather than just
scalars as in the standard.
.SH
Separate compilation
.PP
The compiler
.PC
has been extended to allow separate compilation of programs.
Procedures and functions declared at the global level
may be compiled separately.
Type checking of calls to separately compiled routines is performed
at load time to insure that the program as a whole
is consistent.
See section 5.10 for details.
.NH 2
Resolution of the undefined specifications
.SH
File name \- file variable associations
.PP
Each Pascal file variable is associated with a named
.UX
file.
Except for
.I input
and
.I output,
which are
exceptions to some of the rules, a name can become associated
with a file in any of three ways:
.IP "\ \ \ \ \ 1)" 10
If a global Pascal file variable appears in the
.B program
statement
then it is associated with
.UX
file of the same name.
.IP "\ \ \ \ \ 2)"
If a file was reset or rewritten using the
extended two-argument form of
.I reset
or
.I rewrite
then the given name
is associated.
.IP "\ \ \ \ \ 3)"
If a file which has never had
.UX
name associated
is reset or rewritten without specifying a name
via the second argument, then a temporary name
of the form `tmp.x'
is associated with the file.
Temporary names start with
`tmp.1' and continue by incrementing the last character in the
.SM
USASCII
.NL
ordering.
Temporary files are removed automatically
when their scope is exited.
.SH
The program statement
.PP
The syntax of the
.B program
statement is:
.LS
\*bprogram\fP <id> ( <file id> { , <file id > } ) ;
.LE
The file identifiers (other than
.I input
and
.I output )
must be declared as variables of
.B file
type in the global declaration part.
.SH
The files input and output
.PP
The formal parameters
.I input
and
.I output
are associated with the
.UX
standard input and output and have a
somewhat special status.
The following rules must be noted:
.IP "\ \ \ \ \ 1)" 10
The program heading
.B must
contains the formal parameter
.I output.
If
.I input
is used, explicitly or implicitly, then it must
also be declared here.
.IP "\ \ \ \ \ 2)"
Unlike all other files, the
Pascal files
.I input
and
.I output
must not be defined in a declaration,
as their declaration is automatically:
.LS
\*bvar\fP input, output: text
.LE
.IP "\ \ \ \ \ 3)"
The procedure
.I reset
may be used on
.I input.
If no
.UX
file name has ever been associated with
.I input,
and no file name is given, then an attempt will be made
to `rewind'
.I input.
If this fails, a run time
error will occur.
.I Rewrite
calls to output act as for any other file, except that
.I output
initially has no associated file.
This means that a simple
.LS
rewrite(output)
.LE
associates a temporary name with
.I output.
.SH
Details for files
.PP
If a file other than
.I input
is to be read,
then reading must be initiated by a call to the
procedure
.I reset
which causes the Pascal system to attempt to open the
associated
.UX
file for reading.
If this fails, then a runtime error occurs.
Writing of a file other than
.I output
must be initiated by a
.I rewrite
call,
which causes the Pascal system to create the associated
.UX
file and
to then open the file for writing only.
.SH
Buffering
.PP
The buffering for
.I output
is determined by the value of the
.B b
option
at the end of the
.B program
statement.
If it has its default value 1,
then
.I output
is
buffered in blocks of up to 512 characters,
flushed whenever a writeln occurs
and at each reference to the file
.I input.
If it has the value 0,
.I output
is unbuffered.
Any value of
2 or more gives block buffering without line or
.I input
reference flushing.
All other output files are always buffered in blocks of 512 characters.
All output buffers are flushed when the files are closed at scope exit,
whenever the procedure
.I message
is called, and can be flushed using the
built-in procedure
.I flush.
.PP
An important point for an interactive implementation is the definition
of `input\(ua'.
If
.I input
is a teletype, and the Pascal system reads a character at the beginning
of execution to define `input\(ua', then no prompt could be printed
by the program before the user is required to type some input.
For this reason, `input\(ua' is not defined by the system until its definition
is needed, reading from a file occurring only when necessary.
.SH
The character set
.PP
Seven bit
.SM USASCII
is the character set used on
.UX .
The standard Pascal
symbols `and', 'or', 'not', '<=', '>=', '<>',
and the uparrow `\(ua' (for pointer qualification)
are recognized.\*(dg
.FS
\*(dgOn many terminals and printers, the up arrow is represented
as a circumflex `^'.
These are not distinct characters, but rather different graphic
representations of the same internal codes.
.FE
Less portable are the 
synonyms tilde `~'
for
.B not ,
`&' for
.B and ,
and `|' for
.B or .
.PP
Upper and lower case are considered to be distinct.\*(st
.FS
\*(stThe proposed standard for Pascal considers them to be the same.
.FE
Keywords and built-in
.B procedure
and
.B function
names are
composed of all lower case letters.
Thus the identifiers GOTO and GOto are distinct both from each other and
from the keyword
\*bgoto\fP.
The standard type `boolean' is also available as `Boolean'.
.PP
Character strings and constants may be delimited by the character
`\''
or by the character `#';
the latter is sometimes convenient when programs are to be transported.
Note that the `#' character has special meaning 
.up
when it is the first character on a line \- see
.I "Multi-file programs"
below.
.SH
The standard types
.PP
The standard type
.I integer
is conceptually defined as
.LS
\*btype\fP integer = minint .. maxint;
.LE
.I Integer
is implemented with 32 bit twos complement arithmetic.
Predefined constants of type
.I integer
are:
.LS
\*bconst\fP maxint = 2147483647; minint = -2147483648;
.LE
.PP
The standard type
.I char
is conceptually defined as
.LS
\*btype\fP char = minchar .. maxchar;
.LE
Built-in character constants are `minchar' and `maxchar', `bell' and `tab';
ord(minchar) = 0, ord(maxchar) = 127.
.PP
The type
.I real
is implemented using 64 bit floating point arithmetic.
The floating point arithmetic is done in `rounded' mode, and
provides approximately 17 digits of precision
with numbers as small as 10 to the negative 38th power and as large as
10 to the 38th power.
.SH
Comments
.PP
Comments can be delimited by either `{' and `}' or by `(*' and `*)'.
If the character `{' appears in a comment delimited by `{' and `}',
a warning diagnostic is printed.
A similar warning will be printed if the sequence `(*' appears in
a comment delimited by `(*' and `*)'.
The restriction implied by this warning is not part of standard Pascal,
but detects many otherwise subtle errors.
.SH
Option control
.PP
Options of the translators may be controlled
in two distinct ways.
A number of options may appear on the command line invoking the translator.
These options are given as one or more strings of letters preceded by the
character `\-' and cause the default setting of
each given option to be changed.
This method of communication of options is expected to predominate
for
.UX .
Thus the command
.LS
% \*bpi \-l \-s foo.p\fR
.LE
translates the file foo.p with the listing option enabled (as it normally
is off), and with only standard Pascal features available.
.PP
If more control over the portions of the program where options are enabled is
required, then option control in comments can and should be used.
The
format for option control in comments is identical to that used in Pascal
6000\-3.4.
One places the character `$' as the first character of the comment
and follows it by a comma separated list of directives.
Thus an equivalent to the command line example given above would be:
.LS
{$l+,s+ listing on, standard Pascal}
.LE
as the first line of the program.
The `l'
option is more appropriately specified on the command line,
since it is extremely unlikely in an interactive environment
that one wants a listing of the program each time it is translated.
.PP
Directives consist of a letter designating the option,
followed either by a `+' to turn the option on, or by a `\-' to turn the
option off.
The
.B b
option takes a single digit instead of
a `+' or `\-'.
.SH