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Using SAIL at LOTS
SAIL is a high level programming language based on ALGOL-60. It
is extended to provide string handling, structured data types
(records), associative data (LEAP), easy access to the TOPS-20
input/output features and operating system, and much else.
I. Documentation
This document contains hints on how to write, run, and debug a
Sail program. It is oriented towards users who already know an
Algol-like language, but who are not familiar with the version
of Sail at LOTS. Other documentation available includes:
SAIL User Manual (CSD report STAN-CS-76-574). This is
the basic reference source for programming in Sail, available at
the Stanford Bookstore.
SAIL tutorial (CSD report STAN-CS-76-575). A fairly
readable introduction to programming in Sail.
If you are familiar with ALGOLW and would like a short
discussion of the differences between the two languages you may
be interested in the file DOC:ALGOLW-SAIL.DIFFERENCES at LOTS.
You may read this file with the TYPE command. If you are not
familiar with any Algol-like language, try reading the file
DOC:SAIL-EXAMPLES.TUT at LOTS.
For more information on LEAP, say HELP LEAP.
Note: You will find in the manuals that there is a distinction
between TENEX and TOPS-10 SAIL. Since this is TOPS-20, you will
not know which to expect. The answer is that TOPS-20 is nearly
the same as TENEX. So use TENEX SAIL input/output routines! Or
even better, use a set of prepackaged input/output routines; see
below for a description of one such package, IOSAIL.
II. Writing Sail programs
The first step in running a Sail program is to place the source
of your program in a file at LOTS. To do so, you would normally
use the EDIT program (via the system commands CREATE and EDIT)
to enter and correct the text of the program. See the LOTS
Overview Manual for more information on using EDIT.
This source file should have the extension ".SAI" to indicate
that it contains a Sail source program. All file specifications
for Sail consist of a name-part, a period, and an extension,
plus optional fields to refer to files belonging to other users.
For source programs, the EXEC requires that the name-part
contain six characters or less, and that the extension be three
characters or less. Data files, on the other hand, may have
names and extensions of up to 39 characters each (though it is
conventional to use a .DAT extension for data files).
III. Running a Sail program
To run your program, you must first compile the source into
relocatable object code, then load this object code plus that
for any external routines into your core image, and then either
begin execution or save a copy of the core image for later
execution. There are EXEC commands that perform various
combinations of these steps.
The commands used to run Sail programs are COMPILE, LOAD,
EXECUTE, START, and DEBUG. Most of the time, though, you will
only need to use EXECUTE or DEBUG. Consider the following
sample terminal session:
@create fib.sai
Input: FIB.SAI.1
00100 BEGIN "Fibonacci numbers"
00200 REQUIRE "<sail>iosail.hdr" SOURCE!FILE;
00300 INTEGER a,b,c,i;
00400 a:=1; b:=1;
00500 FOR i:=1 STEP 1 UNTIL 10 DO
00600 BEGIN
00700 Print( a," " );
00800 c:=a+b;
00900 a:=b;
01000 b:=c
01100 END;
01200 Print(crlf,"All done",crlf)
01300 END "Fibonacci numbers"
01400
*e
[FIB.SAI.1]
@execute fib
FIB.SAI.1 1
<SAIL>IOSAIL.HDR.23 1
End of compilation.
LINK: Loading
[LNKXCT FIBONA Execution]
1 1 2 3 5 8 13 21 34 55
All done
End of SAIL execution
A file FIB.SAI was created containing a simple program to
calculate Fibonacci numbers.
Sail is a block-structured language: each program begins with
BEGIN (case is irrelevant) and ends with END. Variables may be
declared in any block, but must be declared before use (among
the types of variable available are INTEGER, REAL, LONG REAL,
STRING, BOOLEAN and RECORD!POINTER. If you follow BEGIN with a
string (String constants are text that is enclosed in double
quotes, e.g., "sdemo1" on line 100), then that string will name
the block. If you follow an END with a string, SAIL will verify
that the string following the END exactly matches the string
following the corresponding BEGIN. If they don't match, SAIL
complains. The strings must match exactly, including the case
of each letter.
Line 200 instructs Sail to include the header file IOSAIL.HDR in
our program. This header file contains declarations for various
standard procedures and constants, for example the CRLF
(newline) that is used in line 1200 to instruct Sail to start a
new line in the output.
After writing the program, we give the EXECUTE command to
instruct the system to compile and run the program. The EXECUTE
command searched for a file with one of the standard source file
extensions, found a .SAI, and therefore called Sail. You could
have optionally typed the file name including the .SAI
extension. (The '.' must be left off or the entire .SAI must be
included though--a plain '.' indicates a null extension, which
counts as having specified an extension.) The Sail compiler
produced a relocatable (object) file with an extension .REL,
which the linkage editor loaded into memory and started running.
When execution has finished, we return to the EXEC.
Some optimization is done in processing the command. If a .REL
exists that is more recent than the source ( .SAI ) file, then a
new .REL file is not created. This includes the COMPILE
command, which then does nothing.
IV. IOSAIL
IOSAIL is a package of procedures and macros designed to provide
simple input/output for Sail programs. It includes definitions
of commonly used string constants such as CRLF (carriage return
followed by line feed) and TAB, a set of easy to use input
procedures, and a set of miscellaneous conversion and debugging
procedures. For details, consult the file DOC:IOSAIL.DOC at
LOTS.
To get all the macros and procedures declared, put the statement
REQUIRE "<SAIL>IOSAIl.HDR" SOURCE!FILE; in the declarations
section of the outermost block of your SAIL program. This will
automatically include <SAIL>IOSAIL.REL in the list of files for
the LOADER. The SAIL sources for the procedures are in
<SAIL>IOSAIL.SAI, the macros and declarations are in
<SAIL>IOSAIL.HDR.
V. Sail character set
In SAIL, special handling of characters not included in the
ASCII standard keyboard set is needed. The following
equivalents apply when comparing the SAIL manual with what you
type on a LOTS keyboard:
SU-AI character standard ASCII
circle times XOR
membership (epsilon) IN
equivalence EQV
_ (in identifiers) !
left arrow := -or- _
VI. Profil
It is possible to get an execution count profile of a SAIL
program (indicating the number of times each statement was
executed), displayed on a listing which is indented to show the
block structure of the program. The method is a bit
complicated, but the result is so often an aid in debugging that
it's worth it. The execution counts and the display of the
block structure each have their own merits.
[1] Compile and execute the program, specifying the /PROFILE
switch. For example, recall our FIB program above:
@EXEC FIB.SAI/PROFILE
The /profile switch causes Sail to write a file of execution
counts, FIB.KNT , when it finishes execution. This file will
be used by the profile program, below.
[2] Call the PROFIL program as follows:
@PROFIL
*FIB_FIB
[3] Now print the profile file on the line printer. It has
extension ".PFL" as in "FIB.PFL" and is of 120 column width.
[2 Alternative] Call the PROFIL program, and specify that output
should go directly to the terminal:
@PROFIL
*TTY:_FIB/T
The /T switch instructs profil to produce a listing formatted
for terminal viewing -- 80 columns wide.
For more information, see page 156, Appendix F, of the SAIL
Manual.
VII. BAIL
Bail exists! (Hooray, hooray!) It is an interactive debugger
for sail programs. You can do things like inserting breakpoints
(to stop at particular places in your program), look at or
change the values of variables at a breakpoint, trace procedure
calls, single-step through the execution of your program, etc,
etc, etc. You will find it a big help in debugging. All the
winning features of Bail are described in pages 144-149 of the
Sail manual.
Using Bail: just (re)compile your program.
@DEBUG FOO.SAI
If you have a recent version of your program, you will have to
force Sail to recompile by saying DEBUG/COMP FOO.SAI instead.
You can get into Bail in four ways.
1. By an explicit call in your program. Declare Bail an
external procedure (via EXTERNAL PROCEDURE BAIL) first, then
call it like a procedure with no parameters.
2. After a Sail-detected error. Type B to the error message.
3. From the monitor, say when you suspect there's an infinite
loop in your program. This is harder so try not to get into
any infinite loops.
4. From a breakpoint, set in some previous Bail interrupt. See
the writeup on the BREAK command in the Sail manual.
Some minor glitches: Bail doesn't know about := . Use _
(backarrow). Use of DEBUG causes Sail to create a file (or
several) with extension .SM1 for Bail's bookkeeping. If
creation of this file sends you over your disk allocation, you
may get a message when Bail is entered during execution about it
not being able to open some files. In this case, the file Bail
is trying to open is named in the error message. To fix the
situation, type CTRL-C and expunge some files, then type the
CONTINUE command and type the name of the file that Bail was
previously trying to open.