2) The CASE command is far more versatile than a replacement for ON...GOSUB. The expression to be tested can be a string expression or logical expression as well as being numerical as in BASIC. In addition where BASIC expects the values taken by the expression to be sequential the CASE command will allow ANY values:

4) Array handling in COMAL is extremely powerful. The DIM statement of COMAL equivalent to that of BASIC looks clumsy but consider that in COMAL the index of an array can range from ANY integer to ANY larger integer:
e.g. DIM FIELD(-3:7) declares a one dimension array with indices from -3 to 7 inclusive.

e.g. DIM NUMBER(6) declares an array with indices 1 to 6 inclusive (there is NOT a 0 element as in BASIC unless declared specifically).
In COMAL the maximum length of a string MUST be defined
e.g. DIM NAME$ OF 10 declares a string of maximum length 10 characters.
e.g. DIM NAME$(2:5,3:7) OF 10 declares a string two dimensional array of 20 elements. each with maximum length 10 characters.
N.B. ALL array variables MUST be dimensioned. There are no defaults as in BASIC.

5) The ENTER command can be used to merge previously LISTed files into the current program:
e.g. ENTER"FILENAME" will merge FILENAME from disk into the current program. Lines will be overwritten and reordered as necessary:
e.g. ENTER"FILENAME",1 will take the file named FILENAME from cassette and merge ir ith the current program.

6) EOD - This is a logical variable which is TRUE when the last item in DATA statements is READ.

7) EOF(X) - This is a logical variable which is TRUE when the last item from channel X is taken..

8) EXEC is more than a replacement for GOSUB. Together with the PROC command e have a very powerful feature. Parameters can be passed to a subroutine. Variables used in a subroutine can be global to the whole program (in which case changes made to the variables in the subroutine will be recognised in the main program), or local to the subroutine (in which case the main program will not recognise any parameters used in the subprogram). All parameters to a subprogram are local unless identified as REF parameters. As output parameters must be recognised by the main program they must be defined as REF parameters. For space limitations all arrays must be defined as REF parameters:

The PROC used as a function is also more powerful than the BASIC DEF FN. In BASIC one can only use 1 line to define the function. In COMAL one can use as many lines as necessary.
9) The IN function. used with strings determines whether one string is contained within another and returns the position of the first character if so. If the string is not found 3 value of O is returned:

11) The command LABEL will cause a label to be placed on a line. For example you can type either of the 2 statements below and the COMAL interpreter will accept it in the same way:

12) The LIST command under COMAL has 2 special features, Firstly it invokes automatic indenting of lines for readability. It is not necessary to type the lines indented it is done automatically. Secondly one can LIST to a file on the disk or cassette. This file can subsequently be merged into any existing program by the ENTER command:
LIST"FILENAME" lists the current program to disk under the same FILENAME.
LIST"FILENAME",1 lists the current program to cassette under the name FILENAME.
LIST 10-50,"FILENAME" will list lines 10 to 50 inclusive to disk under the name FILENAME.

13) The RENUM command will renumber an entire program. It has the same syntax as the AUTO command.

14, The RUN command is similar to that of BASIC with one notable exception. variables are NOT reset to zero or null. Thus no assumptions should be made on the values of undeclared variables in a program.

15) In comparing the BASIC PRINT command with the COMAL equivalent. COMAL looks clumsy. In reality COMAL is much more flexible. BASIC has fixed print zones of length 10. In COMAL one can vary the zone length by the ZONE command:

e.g. ZONE:=5 will cause items separated by commas in print lists to be printed in zones of 5-character length.
The default value of ZONE length is O and not 10 as in BASIC. Thus a comma will cause no separation of variables until zone length has been redefined. In COMAL a semicolon between print items will ALWAYS print 1 space between those items, whether they are numeric or string. It is a true space unlike BASIC which for numerals will print a cursor right after the value. This appears like a space but in reality is not.

16) In COMAL variable names or labels can be up to 16 characters in length. The first character must be a letter and all 16 are recognised unlike BASIC where only the first 2 are recognised. In COMAL it does not matter if a variable name includes a COMAL keyword. Thus variable names can be chosen which have meaning. One side effect of this is that COMAL keywords must be typed with a following space. Otherwise it will be regarded as a variable name and a syntax error will probably result. One other COMAL restriction on variable names is that the same name CANNOT be used for two different variable types. For example the variables A and A$ cannot appear in the same segment of program.

17) I have mentioned above that one need not type the spaces necessary to cause line indentation. They are added automatically when the program is LISTed. There are other things that need not be typed as well. Here is the complete list:

The ':' preceding the '=' in assignment statements. The 'OF' in 'CASE...OF' statements
. The 'DO' in 'FOR...DO' or 'WHILE...DO' statements provided the 'DO' is the last word in the statement.
The 'THEN' in 'IF...THEN' or 'ELIF...THEN' statements provided the 'THEN' is the last word in the statement.
The procedure name following the 'ENDPROC' statement.
In all the above cases the COMAL interpreter will automatically add the relevant words if they have been omitted.

18) The 'REM' command is accepted in COMAL but the interpreter will replace it with //. REM or // can be used at the end of a COMAL statement or be on a line of its own.

19) It has been stated above that variables cannot be assumed to be null at the start of a program. There is therefore a need for a command which will set a string variable to a blank. The following example will illustrate: SPACE$(1:60):="" will set the string SPACE$ of sixty characters length to a blank. Another facility on string handling is that if a single character is to be referenced it can be done simply as the following example shows:
NAME$(5) refers to the 5th character of NAME$. It is not necessary to say NAME$(5:1).
Thus when the length value is 1 it may be omitted.

As can be seen from the above COMAL has many features that BASIC does not have. I have left until last one of the most important features:

There is syntax checking on input . The interpreter will even leave the cursor at the point where the error is recognised so that the line can be modified quickly before continuing. This means all the statements of a COMAL program are checked for syntax before it is RUN. In BASIC they are not checked until run time and it is up to the programmer to ensure all the lines are executed and checked. This is not at all easy on long and complicated BASIC programs with many loops and branches. To sum up COMAL is an extremely powerful language compared with BASIC which results in easy to read, easy to maintain programs.

COMAL - BASIC COMMANDS WITHOUT COMAL EQUIVALENTS

Here is a list of BASIC commands not supported by COMAL:

It will be seen that most of the commands not implemented are BASIC4 disk management commands. The equivalent BASIC2 sequences also do not appear to exist. I find this somewhat surprising as the means to decode tne commands is available in the BASIC ROM.

Here is list of oddities I have found in using COMAL:

1) The command BASIC causes a system error although it is a valid COMAL command.

2) PRINT USING is not implemented. In my opinion the saddest point about using COMAL,

3) SAVE or LOAD to cassette does not work. The commands function but on reloading the file reads as gibberish.

4) When a program with indented lines is ENTERed an error occurs on lines with DIM statements. Just ignore the error. Type <return> over the displayed line and all will continue normally.

5) When a program is ENTERed from tape an EOF error occurs as a matter of course. It is not really an error.

6) ZONE:=1 does not work correctly (it works as if ZONE:=2). Use ZONE:=0 and it works like ZONE:=1 !

7) Do NOT send disk commands when a disk is not switched on. A system crash will occur if you do !

8) DEBUG, while being a COMAL command causes a system error If anybody finds any other problems or has any suggestions as to resolving the above or why they happen, please let me know.

COMAL FOR THE 8096
In this article I want to talk about the additionaL COMAL commands available in the 8096 versions of COMAL

Unless stated otherwise they apply to versions 1.01, 1.02, and the COMAL board version. Version 1.02 represents the full COMAL implementation.

1) It is now possible to say PRINT AT 5,16: SALARY This will print the value of SALARY starting at row 5, column 16. This can also be combined with USING as e.g.

2) BASIC is identical to 0.12 in that a warm reset is carried out. It assumes a BASIC4 machine so would not be valid with a COMAL board in a new ROM PET.

3) The CAT command has been extended to a full specification as follows:

4) CURSOR row,col moves the cursor to the given row and column.

5) DEBUG will jump to monitor, but the routine has a bug in it so you are not advised to use it.

6) DELETE "O:FILENAME" will scratch the file FILENAME from drive 0. The drive number must be given for the command to work This command is also supported by 0.12.

7) ENDFUNC was described for 0.12 last Newsletter. It is not available in 1.01.

8) ENDLOOP is described under the LOOP command. It is not supported by 1.01.

9) ESC was described for 0.12 last Newsletter.

10) EXIT is described under the LOOP command, It is not supported by 1.01.

11) FUNC was described for 0.12 last Newsletter, It is not supported by 1.01.

12) GET$(1,6) will get 6 characters from the logical file number 1 which has been previously opened for READ. One can GET characters from the keyboard by using a file number of O (which need not be opened). Note that at least one character must be returned. Use KEYS(q.v.) if no key press is a possibility. I am unclear as to whether this command is supported by 1.01. GET$ certainly exists in 1.01 but it may act like KEY$.

13) GLOBAL is provided in 1.01 only and allows a CLOSED procedure to use variables from outside. To do this they are defined as GLOBAL inside the procedure.

14) IMPORT is the equivalent of GLOBAL in 1.02 and the COMAL board.

15) INTERRUPT PR0CNAME will execute the procedure PROCNAME if a signal is sensed on the SRQ line of the IEEE bus.

16) KEY$ will return the last '

 17) LOOP is a new structure introduced on 1.02 and the COMAL board. A set of instructions enclosed by LOOP and ENDLOOP will execute continuously. Obviously there must bea way out of the loop. This is by an EXIT command (or possibly EXITIF command, as this may be implemented instead in the final version).

19) NULL is as for 0.12 described last Newsletter.

20) OBJLOAD "FILENAME" will load the file FILENAME into top of memory and lower COMAL pointers accordingly. One can load from tape by adding a unit number (,1).

21) OPTION 9*4096 will recognise the COMAL-compatible machine code procedures written in ROM starting at $9000. OPTION can be used to access any start address, so machine code procedures can be written, loaded with OBJLOAD and recognised via OPTION. Unfortunately I have not seen any instructions on how to implement machine code procedures to use with this powerful facility.

22) PRINT USING is fully supported by these COMAL versions.

23) RENUM is extended:

RENUM 500; 1000,5 will renumber lines from line 500 to the end of the program starting line 1000 in steps of 5. This extension is not implemented in 1.01.

24) RESTORE LABEL will restore the DATA pointer to the first DATA item after the line labelled LABEL.

25) RETURN is as defined for 0.12 in the last Newsletter.

26) SAFE will make a program unlistable. I am not sure if this is implemented in 1.02. In my opinion it shouldn't be implemented at all !

27) LOAD, ENTER, LIST,' SAVE to tape are supported by these COMAL versions.

28) SETEXEC is as described for 0.12 last Newsletter.

29) SETTIME 123 will set the jiffy clock to 123. This is only available on 1 .01 .

30) SPC$ is supported by these COMAL versions and acts like the BASIC equivalent.

31) STATUS$ is similar to DS$ in BASIC4. In version 0.11 or 0.12 STATUS acts like PRINT STATUS$.

32) STOP "MESSAGE" will print the text tMESSAGE' when tne STOP command is executed. This i s not supported by 1 .01.

33) STR$, the BASIC function, is supporred by these COMAL versions.

34) TIME holds the value of the jiff' clock. The 1.01 SETTIME is mimicked in other versions bv TIME 123.

35) TO can be used for readability in the LIST command on 1 .02 or the COMAL board:

LIST 10-266 TO "FILENAME" is identicaL to LIST 10-266,"FILENAME"

36) TRAP is as described for 0.12 last Newsletter.

37) VAL and VERIFY are exactly as the BASIC equivalents.

38) READ FILE, WRITE FILE, INPUT and PRINT to random access files are supported

39) COMAL uses file numbers 1 and 255 for its own use (1 for disk, 255 for printer) so do NOT use these numbers in your programs.

As you can see from the above, these versions of COMAL introduce all the missing items from the earlier software versions. They also provide some very useful extensions and further enhance the suitability of COMAL over BASIC. While the COMAL board is not cheap it certainly will provide a much better programming language than the original BASIC while still allowing BASIC to be used when required. By the time you read this I should have version 1.02 for 8096 computers available on 4040 or 8050 disks.

Brian Grainger.

(or checkout the download section of this website ;-)