8080 Cassette FOCAL User`s Manual
Contents
1. The following is a list of error codes issued by FOCAL The error number represents the address in the FOCAL program where the error was detected ERROR CODE 00 00 00 0D 02 96 02 BB 03 22 03 27 04 43 05 48 05 BE 05 FD 06 1D 06 60 06 08 06 F0 07 39 07 59 07 70 09 85 0A C5 0A ES 0B 39 0B D7 OB EF 0C 18 0C 2D 0C 35 10 79 10 D3 10 EB 11 5E 12 4C 12 51 12 91 12 94 12 97 12 9A 12 9D 12 A0 12 DB 12 DE 12 F6 13 44 13 65 MEANING Mode select restart BUFFER overflow line Bad line number Bad line number Bad character Bad character Stack overflow expression too complex Bad line number No such group DO reference missing line GOTO references missing line Ilegal command Missing left paren in JUMP Missing left paren in IF Left of bad in FOR or SET Excess right paren in FOR or SET Bad expression in FOR No such line number Missing terminator Missing operator before left paren Arithmetic overflow Missing left paren in function reference Missing left paren Mismatched right paren ERASE F Bad argument in Erase Can t raise to a negative power Bad library command Missing comma in OPEN Missing comma after file number Bad file number Bad file number Tape read error or user hit mode select while reading File already open File not open Unit already open Unit not open File name missing End of File encountered Error in read Wri2. e heal L Processor _ 8080 FOCAL User s Manual Processor Technology Corporation 7100 Johnson Industrial Drive Pleasanton CA 94566 Telephone 415 829 2600 Copyright 1977 1978 by Processor Technology Corporation First Printing April 1978 Manual Part No 727025 All rights reserved IMPORTANT NOTICE This manual and the program it describes are copyrighted by Processor Technology Corporation All rights are reserved All Processor Technology software packages are distributed through authorized dealers solely for sale to individual retail customers Wholesaling of these packages is not permitted under the agreement between Processor Technology and its dealers No license to copy or duplicate is granted with distribution or subsequent sale FOCAL is the registered trademark of Digital Equipment Corporation Maynard Massachusetts SECTION 1 TABLE OF CONTENTS PAGE INTRODUCTION taaan 1 1 1 1 GO and QUIT Commands viii iii ed a er a iia 1 2 CONVENTIONS att id Ne aa Des leere hehe 2 1 2 1 INU DSS ctra rt ee a Lt LAS UA LD LL ne Maa de ende Blea dei een 2 1 2 2 NE AAPP UA A II O ee ee 2 1 2 3 Ey lu tins Expressions ies 2 2 2 4 Math Funct O18 a A Mie ds e LS IEE dE Be 2 2 2 5 Eine Interpretation 2 Na 2 3 IHESEFEOMMANDE SSH er e Pee tet Lire thane Baia 3 1 INPUT OUTPUT COMMANDS Srita dilatado did lidad 4 1 4 1 Phe TALE Command o E 4 1 4 2 The ASK Command di iii did 4 2 BRANCH COMMANDS oo da 5 1 5 1
3. B C B 3 D INPUT THE 122 SEI PROGRAM x generalized program 999 QUIT SET B 10 1 SET C 12 77 SET D 60 SET PARAMETERS GO RUN THE PROGRAM results EXAMINE RESULTS SET B 10 6 SET C 11 SET D 100 MODIFY PARAMETERS GO RERUN THE PROGRAM results EXAMINE 3 1 FOCAL 4 INPUT OUTPUT COMMANDS 4 1 The Type Command Every FOCAL program must contain at least one TYPE statement if it is to produce printed results The TYPE statement prints values of variables text strings and results of expressions These can be combined using commas to separate the items into a list The following example shows several TYPE statements and their resultant printout SET A 1 SET B 2 SET AB 6 TYPE A 000000 PE A B AB 1 000000 2 000000 6 000000 TYPE QUOTATION MARKS START AND END TEXT T 0 p TY QUOTATION MARKS START AND END TEXT TYPE A 1 000000 TYPE NOTE HOW THE AND WORK NOTE HOW THE TYPE A B 1 000000 AND WORK 2 000000 TYPE 5 02 AB hi 12345 5456 6 00hi2345 55 The examples are in immediate mode where their results were immediately visible The only modification for program storage would be the addition of line numbers It is important in the examples to watch how the special characters comma and are
4. 98 only the integer part is considered The values 2 37 and 2 98 would both transfer control to the third statement listed The following shows this command being used to select a part of a program given some input from the user 1 2 ASK 1 RIGHT 2 LEFT 3 UP 4 DOWN 5 NO CHANGE N 1 4 JUMP N 1 10 1 15 34 12 3 65 98 2 02 If the computed value of the bracketed variable or expression is less than zero control goes to the first statement listed and if it s too large for the list FOCAL sends control to the last statement listed If the user had responded 5 or larger to the ASK statement above control would have gone to the statement numbered 2 02 5 2 FOCAL 6 SUBROUTINES 6 1 The DO And RETURN Commands A subroutine sometimes called a routine is a special sequence of statements with the same group numbers A group number as mentioned is the integer part of a statement s line number and the fractional part is the step number A subroutine for instance could be the sequence of statements between line numbers 52 01 and 52 99 This sequence is special because any part of the program can send control to this block of statements and receive it again when the block the subroutine has finished The sending of control is known as a subroutine call and the process used for a subroutine to return this control to the code which called it is a return from subroutine In FOCAL the subroutine is thrown into execution by the DO sta
5. This very powerful ability is represented in FOCAL by three commands GOTO IF and JUMP These can alter the program flow rather than executing statements in their numeric order The computer can send control to a program line number specified in the command These commands differ in that GOTO always transfers control to the single statement number given to it while JUMP and IF transfer to one of a number of possible statements based on a test 5 1 The GOTO Command In the following example the GOTO statement sends control back to a statement that counts the number of times it has been executed Readers new to programming are strongly advised to follow the example and the results closely 1 1 SET N 0 1 8 SET N N 1 1 6 TYPE LOOP NUMBER N 1 27 GOTO LS GO LOOP NUMBER 1 000000 LOOP NUMBER 2 000000 Unfortunately this program never ends and the programmer will never see the READY asterisk from FOCAL Program segments which repeat are called loops The program shown above is an example of an infinite loop To escape such a loop type MODE and the program will stop GO GOTO starts a program at the line number specified or at the lowest line number in the program if no line number follows The GOTO statement can also be used in the immediate mode to transfer control to the program In the next example the instruction GOTO 1 8 passes control to statement 1 8 and starts the loop with the loop counter alr
6. Ti GOTO Command eiaeia A e Ed de o a 5 1 5 2 The TE SA a 5 1 5 3 The JUMP temita 5 2 SUBROUTINES ii bdo 6 1 6 1 The DO and RETURN COMMAN GS 0 sense 6 1 LODOS e O UDB u IR AU TOY RET e CEU CRU CRT O 7 1 7 1 The FOR COMME 7 1 7 2 Subseripted Variables ooo an 7 2 7 3 The COMMENTS Ai as 7 3 SUPERVISORY BUINC TIONS renen e r A E E 8 1 8 1 The WRITE Command sir its 8 1 8 2 The ERASE Command eneren ee en ee ee nee re ei 8 1 8 3 The MODIFY Eomm nd added die 8 1 8 4 Focal Library og a n a AYN Ta K PPE A A ss 8 1 8 5 The TRACE Fe t re nnd aenn an an a al n nas 8 3 RUNNING BOGA De nc 9 1 9 1 Hardware Requirements arar 9 1 9 2 About Cassette RECOrders ii 9 1 9 3 Miscellaneous Notes O a N EEE EN RT 9 2 9 4 NN 9 3 i FOCAL 1 INTRODUCTION FOCAL is the name of a computer language as well as the name of the program which translates and executes programs written in that language The program FOCAL belongs to a class of language processors called interpreters and this means that FOCAL while operating has complete control of the machine and thus can assist in storing editing and running programs Externally FOCAL communicates with a user through an input output device like a teletype Internally it divides up memory into three sections containing the FOCAL program itself the user s stored program and any variables the user may have created A minimum memory size of 8K is necessary for FOCAL and additional memory allows FOCAL to st
7. have caused incorrect code to appear in memory the message CHECKSUM TEST FAILED will appear The error may not be serious and FOCAL may be used but it is best to try reloading the tape correcting hardware problems if present 9 2 About Cassette Recorders Successful and reliable results with cassette recorders require a good deal of care Use the following procedures 1 Use only a recorder recommended for digital usage For use with the Processor Technology Sol or CUTS the Panasonic RQ 413 AS or Realistic CTR 21 is recommended 2 Keep the recorder at least a foot away from equipment containing power transformers or other equipment which might generate magnetic field picked up by the recorder as hum 3 Keep the tape heads cleaned and demagnetized in accordance with the manufacturer s instructions 4 Use high quality brand name tape preferable a low noise high output type Poor tape can give poor results and rapidly wear down a recorder s tape heads Bulk erase tapes before using 5 Keep the cassettes in their protective plastic covers in a cool place when not in use Cassettes are vulnerable to dirt high temperature liquids and physical abuse 6 Experimentally determine the most reliable setting for volume and tone controls and use these settings only 7 On some cassette recorders the microphone can be live while recording through the AUX input Deactivate the mike in accordance with the manufacturer s instructions In
8. then wait for more commands 3 DELETE This deletes the last character in the line Successive DELETE s delete characters in order from right to left towards the line number 4 CNTRL X This deletes everything in the line up to and including the last character printed The rest of the line as yet imprinted remains intact It will be shifted over however so that it follows the line number 5 RETURN This deletes anything to the right of the last character last printed 6 LINE FEED This instruction tells MODIFY to save the line as presently defined 8 4 FOCAL Library Commands Processor Technology Cassette Focal has an interface with SOLOS CUTER to save and recall programs and data from cassette files This interface is through a series of LIBRARY statements 8 1 FOCAL LIB SAVE lt file name gt Save current program LIB LOAD lt file name gt Get program from tape LIB OPEN lt gt lt file name gt Open a data file LIB TYPE lt gt lt var list gt Type data to file LIB ASK lt gt lt var list gt Ask for data frost file LIB REWIND lt gt Rewind a data file LIB CLOSE lt gt Close data file LIB QUIT Return to SOLOS CUTER lt file name gt is any valid SOLOS CUTER file name of 1 to 5 characters with an optional unit specifies lt gt is a digit between 0 9 lt var list gt Valid FOCAL variable list which may contain constants variables and expressions for TYPE just variabl
9. to the semicolon is ignored by FOCAL Since these statements have line numbers branches can be In this case comments can be thought of as being continue statements as in FORTRAN made to them KEI 19 20 20 x20 20 ELO 6 20 20 220 2 08 20 20 720 20 x 20 20 520 60 60 60 60 60 60 60 60 60 6 0 60 1 2 05 07 09 24 81 83 88 aa OAQHPANAANAANAAA QAAQHHHANAANAA POLYNOMIAL GRAPHING PROGRAM DOCUMENTED VERSION PREPARE SCALING VALUES THAT RELATE THE SIZE OF THE PHYSICAL GRAPH TO THE FUNCTION VALUES TO BE PLOTTED LX 40 S LY 70 S YN 0 S YX 100 XN XX ARE THE MINIMUM AND MAXIMUM X VALUES YN YX ARE THE MINIMUM AND MAXIMUM Y VALUES XN 0 S XXS 100 COMPUTE LENGTH BETWEEN SPOTS ON PLOT BY COMPARING BOUNDS TO LENGTH AND WIDTH SX XX XN LX S SY YX YN LY INPUT PARAMETERS FOR THE POLYNOMIAL DEFINE A B C FOR AX 2 BX C A B C GRAPH Y AX 2 BX C X DOWN Y ACROSS ACH LOOP OF 20 9 DOES 1 LINE OF PLOT XN SX XX DO 60 0 THIS ROUTINE COMPUTES POLYNOMIAL FOR WHATEVER VALUE OF X IS PASSED ITS THEN PLOTTED IF POSSIBLE WITHIN THE DEFINED BOUNDS Y X 2 A B X C IF Y VALUE T00 LARGE OR TOO SMALL PLOT ON EDGES Y YX 60 5 S Y YX G
10. 60 8 YN Y 60 8 S Y N G 60 8 wpe PRINT ASTERISKS UNTIL INDEX AS LARG J YN SY Y T FINISH THIS LINE WITH CR AND RETURN FOR NEW X Ea AS Y T 7 4 FOCAL 8 SUPERVISORY FUNCTIONS 8 1 The WRITE Command For editing purposes FOCAL provides the ability to print all or parts of the program text with the WRITE command It can be used to print single lines or subroutines WRITE 2 2 will print just the line which is numbered 2 2 WRITE 2 0 will print only the lines between 2 01 and 2 99 and the command WRITE ALL will print the entire program ordered by increasing line number 8 2 The ERASE Command The ERASE command is used to delete lines or groups of lines from a program To erase a single line from the text the user only has to type ERASE followed by the line number as in ERASE 22 34 To erase an entire group of lines such as a subroutine the user can type ERASE followed by the group number To delete a subroutine with the group number 95 the user should type ERASE 95 0 ERASE can also he used to clear an entire program its variables and their values This is only done when the user wants to write a new program The ERASE ALL releases all the memory assigned to the last program so that it can be used by the new one It is naturally a good habit to save any lengthy programs on cassette tape before erasing them 8 3 The M
11. OCAL then issues a question mark for the next variable to be defined and so on Text is printed as encountered in the command In use this looks like 70 6 ASK DEFINE STARSHIPS X Y Z COORDINATES X Y Z 70 61 ASK DEFINE X Y Z FOR KLINGON SHIP XK YK ZK 70 65 SET XD XK X SET YD YK Y SET ZD ZK Z 70 66 SET DIST FSOT XD XD YD YD ZD ZD 70 69 TYPE DISTANCE TO ENEMY IS DIST LIGHT YEARS GO DEFINE STARSHIPS X Y Z COORDINATES 4 5 6 DEFINE X Y Z FOR KLINGON SHIP 9 4 1 DISTANCE TO ENEMY SHIP IS 7 141429 LIGHT YEARS The ASK command also has provisions to allow a defined value to remain unchanged The user can type the ESCAPE key in response to the question mark and the corresponding variable will be unchanged Typing a carriage return will result in the variable being set to 0 Typing an expression which may even contain variable and functions will cause FOCAL to evaluate the expression and assign the resulting value to the variable in question ASK will continue to issue question marks for the remaining variable in its list Although the user follows each entry with a carriage return a line is advanced during an ASK command only when a colon or exclamation point appears in the statement 4 2 FOCAL 5 BRANCH COMMANDS The computer s ability to alter the sequence of commands it will execute is known as branching
12. ODIFY Command The MODIFY command is used in immediate mode to edit portions of lines in a FOCAL program It accepts a line number designating the statement to be edited this line number must be followed by a carriage return The actual editing is performed on the line following the MODIFY command The user must guide the MODIFY editor with certain non printing commands After the carriage return MODIFY waits for the user to type a single character from the keyboard this character will be used as the search character MODIFY will print the line in question up to and including this search character or the user can direct modify to perform one of several other tasks described below Each of these tasks is selected with a special character which is typed after the search character If MODIFY does not recognize this character as being a member of its special list it assumes that a text insertion is being made 1 CNTRL G This does nothing to the text already defined but prepares the MODIFY function for a new search character This new search character must follow immediately neither will be printed Any searches through the rest of the current line will use this new character 2 CNTRL L or FORM FEED This command restarts the search procedure in MODIFY which will begin typing the rest of the line until the current search character is found As in the first search sequence undertaken by MODIFY the search chyracter will be typed and MODIFY will
13. URN 70 26 C SET INITIAL POSITION OF MOVING SQUARE 70 28 S NX NR S NY NC 70 30 C LOOP THROUGH NEXT SQUARES ON CHOSEN DIRECTION 70 232 S NX NX DX LP S NY DY LP 70 34 C SEE IF YOU RE STILL ON THE BOARD 1 lt or to NX NY lt or to 8 70 36 I NX 70 24 70 24 I 9 NX 70 24 70 24 70 38 I NY 70 24 70 24 I 9 NY 70 24 70 24 70 40 C CALCULATE POSITION INDEX IN BOARD FOR THIS SQUARE NX NY 70 42 S SQ BD NY 1 8 NX 70 43 C MULTIPLY BY BISHOP S VALUE TO CHECK SIGNS 70 44 S PR SQ BT I PR 70 46 70 32 70 24 ATEO 4 5 C FOUND OPPONENT COUNT IT AS THREATENED LOOP AGAIN 70 46 S ZAP ZAP 1 DO 71 0 70 50 G 70 24 C END OF SUBROUTINE ATL C PRINT OUT THREATS MONITOR PROGRAM PROGRESS AT 2 T PIECE AT ROW NX COLUMN NY IS THREATENED BY 71 25 T PIECE AT NR NC TVS R FOCAL allows subscripts to have any values from 2047 TO 2047 7 3 The COMMENT Statement FOCAL allows comments to be inserted into a program with the C command This command requires a line number as any other command in a stored program but when FOCAL encounters this statement it simply 7 3 FOCAL skips to the next command This statement begins with a line number the letter C and at least one blank following the C The rest of the line up
14. both program store mode and immediate mode FOCAL also allows for efficiency s sake abbreviated commands thus for example SET GO and QUIT could all be written as S G and Q Internally all commands are identified by their first letter only so that SHAKE GASP and QUAKE could be used for SET GO and QUIT All of these statements and their functions will be described shortly To simplify the command recognition process the FOCAL language has been constructed with a mild emphasis on blanks In the commands to be discussed in the upcoming sections all must begin with an easily recognized word or abbreviation like SET GO ASK and Q This word called a KEYWORD must be followed by at least one blank This is acommon source of error for people new to the language Line numbers in stored programs also require a trailing blank for the same reason Most of the FOCAL language statements will expect a sequence of characters following the keyword and its blank The form and content of this part of the statement will depend on the command in question Those commands not requiring more than the keyword will ignore anything between the keyword and the next semicolon or carriage return Telling FOCAL to QUIT YER COMPLAININ will only cause it to QUIT Telling it to GO TO HEAVEN will cause an error because TO HEAVEN is not the line number expected by the G or GOTO command For the same reasons GO TO 5 1 will
15. e will be deactivated If seen while trace is OFF the trace mode will be turned ON 8 3 FOCAL 9 RUNNING FOCAL 9 1 Hardware Requirements In order to run FOCAL an 8080 based computer must be equipped with at least 8K of resident random access memory and the SOLOS or CUTER monitor program The memory should be addressed starting at zero continuously to 8K FOCAL is set up to use 16K of memory allowing more than 9K for programs and data More than 16K can be used by changing memory locations 0006 and 0007 to contain the highest address of continuous available memory For example if 20K 5000 Hex is available enter the following into memory ADDRESS 0006 OOH 0007 50H These values may be changed any time after loading FOCAL The number of memory locations used by any stored program can be calculated from the rule SIZE 8S C 4L where S is the number of variables C is the number of characters in the stored program text and L is the number of lines in the program FOCAL can be SAVEd with the new value if desired FOCAL is saved on cassette in CUTS format which may be read by any Sol computer or any other computer with a CUTS module and the CUTER monitor program To load FOCAL use the command XEQ FOCAL lt CR gt in SOLOS CUTER command mode When FOCAL is first loaded into memory it checks itself in memory by the use of checksums If the tape has been damaged a bad memory location is encountered or other hardware problems
16. eady equalling 12 1 1 SET N 0 1 3 SET N N 1 1 8 TYPE LOOP NUMBER N 1 9 GOTO 1 3 SET N 12 GOTO 1 8 LOOP NUMBER 12 00000 LOOP NUMBER 13 00000 LOOP NUMBER 14 00000 LOOP NUMBER 15 00000 5 2 The IF Statement In the above example the program will again cycle indefinitely since it has no condition for ending itself For this reason FOCAL includes the IF command which transfers control CONDITIONALLY The basic form of an IF statement is lt line number gt IF lt expression gt L1 L2 L3 where L1 L2 and L3 represent statement numbers and the expression always enclosed in parentheses stands for a single variable or arithmetic formula containing variables 5 1 FOCAL When FOCAL encounters an IF statement and the value in parentheses is negative the control is transferred to the first statement number in the list If the value is zero control goes to the second and if it s greater than zero it transfers to the third FOCAL recognizes abbreviated forms of the IF statement containing one or two statement numbers rather than three Should the IF statement only contain 2 statement numbers in its transfer list control will be given to the statement following the IF statement when the value is greater than zero Similarly when an IF statement contains only one statement a value greater than or equal to zero will have control transferred to the next sequential command These differe
17. er line numbers as the program logic allows The running program can be stopped by the user by FOCAL or by the program itself regardless of the reason control will pass to the READY mode of FOCAL at the conclusion of the run The program can stop itself with the QUIT statement which can be stored anyplace any number of times throughout the stored program The instant this statement is executed the program stops and returns control to FOCAL which will issue a ready prompt to signal the end of the program The program is not altered in any way by running so that it can be immediately re run if desired Examples of the GO and QUIT statements appear all throughout this manual In the event the program begins acting in some undesirable way the user can halt the program by typing MODE this can also be done by hitting the CNTL key and the simultaneously FOCAL should respond with the READY prompt if not the program has managed to annihilate part of the program FOCAL and FOCAL will have to be reloaded FOCAL will stop a program if an error is discovered or the program executes its highest numbered line and does not jump back into the rest of the program In this latter case FOCAL tries to find a higher numbered line and failing it returns to the ready mode with an asterisk Errors terminate a job with question marks and an error code which can be deciphered with the table given in a later section 1 2 FOCAL 2 CONVENTIONS 2 1 Numb
18. ers All numbers in FOCAL are internally treated as floating point numbers occupying four memory bytes apiece The largest number which can be represented by FOCAL is 3 6 times 10 to the 38th power and the smallest non zero positive number is 2 7 times 10 to the minus 39th power This same range applies to negative numbers as well The accuracy for a number anywhere in this range is limited to approximately 7 decimal places making 850 0000 equivalent to 850 00003 Any number can be given to FOCAL as an integer without a decimal point as a floating point number a number containing a decimal or as a number in scientific notation Numbers in the scientific notation format consist of a mantissa and an exponent the mantissa is written in decimal form followed by an E followed by the exponent value In the scientifically formatated number 7 2E 11 the number 7 2 is the mantissa and 11 is the exponent The value of this number is 7 2 times 10 to the 11th power or 000000000072 Any form of number input may be signed or or unsigned In FOCAL the following numbers are equivalent 700 3240 700 32403 7 003240E2 7 00324E 2 0 7 00324E01 0 70 0324E01 0 700324 0E 3 0 0700324E4 All numbers printed by FOCAL can contain up to 7 decimal digits excluding the sign 2 2 Variables A variable is a uniquely named storage location having an associated arithmetic value Its name consists of a sequence of letters and or numbers
19. es for ASK Must not contain quoted text ES ME ae or mp All LIBRARY commands may appear in a program or may be used in the immediate mode Except for L TYPE and L ASK none of the library commands should precede other commands on the same line since the rest of the line will be ignored The L LOAD command may be used within a program to chain to another program This will be discussed more fully under LIB LOAD below Naturally all library commands can be abbreviated For example LIB CLOSE 5 can be written as LC 5 Due to the fact that only two cassette drives can be used at one time only two files can be open at one time one on each unit Whenever lt filename gt is specified it may be followed by an optional and a unit number indicating which tape drive to use If no unit is specified then tape unit 1 is assumed For example LIB OPEN 5 TUNA 2 Opens th fil TUNA on cassette drive 2 LIB LOAD FISH Loads the file FISH from cassette drive 1 LIB SAVE lt file name gt will save an exact copy of the internal form of the current program in memory onto file lt file name gt LIB LOAD lt file name gt will load in the data in the file over any program which is currently in memory If the LIB LOAD command was issued from a program the newly read in program will he executed starting at its lowest line number This allows chaining of FOCAL programs To pass data from the first program to the second it sh
20. force an error because TO 5 1 is not a legal line number This command will be described later 2 3 FOCAL 3 THE SET COMMAND The most fundamental command in FOCAL is the SET command In its general form it looks like lt line number gt SET lt variable gt lt expression gt This command can also be used in the immediate mode by omitting the line number The variable names X Y Z and D in the example below are defined by FOCAL and are given values 25 1 6 88 etc A memory location is associated with the variable name If the specified variable name has not yet been encountered by FOCAL a new memory location is set aside and is associated with the name 10 4 SET Z 12 01 10 5 SET X 25 1 10 6 SET Y 6 88 10 7 SET D FSOT X X Y Y 2 Z GO After the program has been run and FOCAL returns to the ready mode the memory location for the variable D from above contains the value of the expression FSQT X X YFY Z Z The execution of the SET command produces the same results whether the command was stored and executed or executed in immediate mode It is often very effective to use the command in both ways during a series of runs with a program Before the RUN command is given the controlling values for the problem can be set or defined allowing the program to be very general The following illustrates a typical sequence of runs using this feature LL SET A FSOT
21. he following is a list of the function names recognized by FOCAL throughout this list the character X represents the argument 2 2 FOCAL FUNCTION USE FABS X ABSOLUTE VALUE FSGN X SIGN OF X VALUE RETURNED IS 1 WHEN X IS NEGATIVE 0 WHEN X 0 AND 1 WHEN X gt 0 FITR X INTEGER PART OF X FRAN X RANDOM NUMBER BETWEEN 5 and 1 0 WITH RANDOM SIGN FATN X ARC TANGENT FEXP X EXPONENTIAL E X FLOG X NATURAL LOG FSIN X SIN OF X FCOS X COSINE OF X FSOT X SQUARE ROOT OF ABSOLUTE VALUE OF X FHYS X HYPERBOLIC SIN FUSR X USER DEFINED WHEN UNDEFINED THIS RETURNS THE VALUE OF THE ARGUMENT UNCHANGED In a statement of the form SET Y FSIN PHD the variable Y is given the computed value of the sine of the angle PHI All of FOCAL s trigonometric functions assume that their arguments are given in radians FATN returns a radian value from minus pi to pi To convert degrees to radians simply divide by 57 29579 2 5 Command Line Interpretation FOCAL allows and even encourages the programmer to put more than one statement on an input line The additional commands statements need to be separated by semicolons and in one case the FOR statement the entire line must be ended with a semicolon This multiple statement line feature can be used in
22. is program as shown then modify both the program and the data as desired The term loop refers to any sequence of statements which can be executed repeatedly the FOR statement is only one way of forming a loop A common way of setting up a loop uses SET IF and GOTO statements in such a way that a counter or loop index an increment value and a limit are manipulated by the program directly The following shows the code necessary for such a loop 7 1 FOCAL 23 25 C INDEX IN IS SET 1 INCREMENT LOWER THAN 1ST VALUE LOS SET IN 0 ELA dk C INCREMENT LOOP INDEX 24 11 IS LOOP START 24 4 SET IN IN IC 25 C TRANSFER OUT OF LOOP WHEN INDEX EXCEEDS LIMIT 252 IF IN LIMIT 27 6 2D 1 C HERE STARTS THE CODE FOR THE BODY OF THE LOOP 42749 GOTO 24 4 C FORCE NEXT LOOP 21 2 6 C THIS STATEMENT IS OUT OF THE LOOP BOTT C REST OF PROGRAM CONTINUES FROM HERE Another example is given in the next section on subscripted variables 7 2 Subscripted Variables The variables in a program generally represent the physical entities of the problem under study The programmer can think of his variable T as containing the current time in seconds or another variable SP as representing a vehicle s speed This association between variables and their physical meaning is fundamental to any type of compu
23. ist of all files on a cassette Exit FOCAL using L Q type CAT lt CR gt rewind to the beginning of tape and press PLAY on the recorder As the header of each file is read information will be displayed on the screen If you have recorded the empty file called END as suggested you will know when to search no further If you write down the the catalog information along with the tape counter readings and a brief description of the file you will be able to locate any file quickly After completing the catalog you may re enter FOCAL by typing EX 0 lt CR gt 13 Before beginning work after any modification to the system test by SAVEing and GETting a short test program This could prevent the loss of much work 9 3 Miscellaneous Notes Should you accidentally leave FOCAL before saving your program you can restart it by typing EXEC 0 to SOLOS or CUTER without losing the program FOCAL does not understand lower case letters All variables commands functions etc must be in UIPPER CASE Lower case is okay within quotes or file names Remember that binary arithmetic is not exact it is only very close Therefore you may expect very small but nevertheless disconcerting errors such as T 23 31 54 00001 which are caused by FOCAL s attempts at rounding off numbers which it cannot store exactly You can make these errors much less frequent by not printing as many digits to the right of the decimal point See TYPE 9 2 FOCAL 9 4 Errors
24. nstance SE X CA A B C B 2 6 SE X CA A B C B 2 6 SE X CA A B C B 2 6 all contain legal expressions Each will however use a different sequence of multiplications additions etc which will produce a different value for the variable X The internal sequence of steps for evaluating the last of the above examples would be ADD A TO B PUT SUM IN TEMPORARY LOCATION 1 TEMP ADD C AND B SUM TO TEMP 2 DIVIDE VALUE IN TEMP2 by 2 6 AND STORE QUOTIENT IN TEMP2 MULTIPLY CA BY TEMP1 PRODUCT STORED IN TEMP 1 MULTIPLY TEMP1 BY TEMP2 PRODUCT STORED IN X OP Gn The level of a nest or Level number is equal to the number of left parentheses minus the number of right parentheses found to the left of the term in question FOCAL as shown evaluates the terms with the highest level number first and works down from there Any level of nesting is allowed as long as the statement occupies only one line 2 4 Math Functions FOCAL provides eleven standard math functions along with a user defined assembly language function A function is a routine internal to FOCAL which performs an arithmetic calculation on a value called an argument which is given to it This argument must be enclosed in parentheses immediately following the functions s name FOCAL s generality permits this argument to be a constant variable or expression T
25. nt styles of IF statements are shown in the following examples 1 2 IF A B 1 5 1 4 1 3 1 3 TYPE A IS GREATER THAN B QUIT 1 4 TYPE A IS EQUAL TO B QUIT 1 5 TYPE A IS LESS THAN B QUIT 22 1 IF MONEY 22 28 22 28 TYPE YOU STILL HAVE FUNDS 22 3 DO 24 0 GOTO 15 4 T 40 6 IF II 40 8 DO 70 0 GOTO 40 6 40 8 TYPE II IS FINALLY NEGATIVE GOODBYE 40 9 QULT Note in the above that a space always separates the IF and the open parenthesis mark These examples are shown only to exercise the various aspects of the IF statement They are not meant to be working parts of a single program 5 3 The JUMP Statement The last of the branch instructions is the JUMP command This statement is frequently used when a program needs to transfer to one of more than three locations The general form of this multibranch instruction is lt line number gt JUMP lt expression gt L1 L2 L3 L4 Ln L1 through Ln are the statement numbers much like those in the IF command definition but there may be as many numbers given as can fit in the command line EXPRESSION as before is any single variable or arithmetic combination of variables If the value of the expression equals 0 control transfers to the first statement number given When the value equals 1 the second statement number is chosen and so on Should the value contain a fractional part like 2 37 or 2
26. ntation If a appears in the list of things to print not in quotes FOCAL will print out all the variables in use and their corresponding values The terminates the print list that is anything following it won t be printed 4 1 FOCAL A very powerful use of the TYPE statement comes from its ability to print the result of whole expressions This means your computer can be used as a super calculator which understands variables This capability is generally used in the immediate mode as shown below The variables used are the same as those stored for use by the program TYPE 542 16 400 0000 TYPE FSOT 2 D 32 5 000000 TYPE TIME TO FALL D FEET IS FSOT D 16 SECONDS TIME TO FALL 400 0000 FEET IS 5 000000 SECONDS SET D 144 TYPE TIME TO FALL D FEET IS FSOT D 16 SECONDS TIME TO FALL 144 0000 FEET IS 3 000000 SECONDS 4 2 The Ask Command Input to a FOCAL program is handled by the ASK command It is used in stored programs to define or redefine the values of program variables The command can contain a text string and a list of variables No expressions may appear in the ASK command although they are allowable responses to the command When executing an ASK FOCAL issues a question mark to request a value The value or expression for which FOCAL can compute a value must be followed by a carnage return F
27. ore larger programs and more variables The additional machine requirements are described in the section called Running FOCAL The user controls FOCAL by typing a line of characters followed by a carriage return The input line can be a command to FOCAL which it must execute immediately or it could be a program line to be stored for later execution These types of input lines can be intermixed as there is no interference between them An input line which is to be stored as a program statement must begin with a number identifying its location within the program A line without a number is not stored but executed immediately FOCAL determines the order of execution for lines in the stored program from their line numbers not the order they were typed which makes adding or replacing lines during a debugging session very easy The following sequences listed as they were input will both result in the same sequence of calculations 1 0 SET A 1 2 0 SET B A 3 2 2 21 SET C A B 4 0 SET X A C 2 2 21 SET C A B 1 0 SET A 1 4 0 SET X A C 2 2 0 SET B A 3 2 The digits to the left of the decimal point in a line number make up what is called the GROUP NUMBER and can be used in some statements to identify a block of statements The digits to the right of the decimal are known as the STEP NUMBER and these have no special significance step numbers can be assigned values in the range 01 to 99 0 and 00 are illegal Groups of
28. ould be written onto a data file by the first program using LIB TYPE see below and read back from the same file number by the second program using LIB ASK It is not necessary to re OPEN the data files during a chain as long as the same file numbers are to he used in both programs When chaining variable s values are lost unless they are saved on a data file LIB OPEN lt gt lt file name gt is used to set up a data file for subsequent LIB TYPE or LIB ASK statements The opened file is assigned the number lt gt and this number must be used to refer to the file in any subsequent data file operations such as TYPE REWIND etc LIB TYPE lt gt lt var list gt is similar to the regular TYPE command except that its output goes to file lt gt where the number lt gt has been assigned to a file using the LIB OPEN command In addition only numerical data can be written to a FOCAL data file no quoted text or The data is written to the file in binary form 4 bytes per number This data is written starting at the current cursor position for the file For example the sequence 8 2 FOCAL LIB OPEN 5 POTTS LIB TYPE 5 A B 10 9 1024 LIB CLOSE 5 results in the values of the three expressions A B 10 and 9 1024 being written to the beginning of the file POTTS LIB ASK lt gt lt file name gt is used to read values from a file which LIB TYPE has written on The number lt gt must have previo
29. some cases this can be done by inserting a dummy plug into the microphone jack 8 If you record more than one file on a side SAVE an empty file named END for example after the last file of interest If you read this file header you will know not to search beyond it for files you are seeking 9 Do not record on the first or last 30 seconds of tape on a side The tape at the ends gets the most physical abuse 10 Most cassette recorders have a feature that allows you to protect a cassette from accidental erasure On the edge of the cassette opposite the exposed tape are two small cavities covered by plastic tabs one at each end of 9 1 FOCAL the cassette If one of the tabs is broken out then one side of the cassette is protected An interlock in the recorder will not allow you to depress the record button A piece of tape over the cavity will remove this protection 11 Use the tape counter to keep track of the position of files on the cassette Always rewind the cassette and set the counter to zero when first putting a cassette into the recorder Time the first 30 seconds and note the reading of the counter Always begin recording after this count on all cassettes Record the beginning and ending count of each file for later reference before recording a new file after other files advance a few counts beyond the end of the last file to insure that it will not be written over 12 The SOLOS CUTER command CATalog can be used to generate a l
30. statements will later be referenced by certain commands by a group number followed by a zero step number The reader should note that there is no single line in the program with a zero step number this number refers to the entire block having that group number Most computer systems draw a distinction between commands and statements Commands are input lines given to a program usually called an operating system which controls the entire machine Statements on the other hand are lines written in a strictly defined language and these are interpreted by a program subordinate to the operating system this program could be a compiler an assembler or an interpreter FOCAL is unusual in that it has the functions of both an operating system and an interpreter and this gives it an enormous flexibility It can handle both statements from the language FOCAL and commands of a supervisory nature This distinction between operating systems and interpreters statements and commands is further weakened because FOCAL allows statements from the language to be executed immediately much like commands in other machines This manual will put little emphasis on the differences between commands and statements in fact the terms will be used almost interchangeably At any given instant FOCAL will be in one of three states or operating modes READY EXECUTION or PROGRAM INPUT FOCAL enters the READY mode after it finishes the last command given to it and as it enters
31. te operation not valid on this file Name too long Bad unit number 9 3 FOCAL
32. tement and the return from the routine by a RETURN statement The DO statement must specify a line number containing the group number for the subroutine to be called and a step number of zero thus DO 52 0 is acceptable whereas DO 52 is not The RETURN statement requires no arguments it simply returns control to the statement following the DO statement which called it Note in the example below that 1 the same subroutine can be called from many places and 2 a subroutine may call another subroutine which may call yet another which etc 10 1 DO 20 0 DO 18 0 10 2 C IF J NOT RIGHT CALL 20 0 AGAIN D0 3 TF eu 10 447 KE20 TS D0 200 0 20 1 F I 1 10 DO 15 0 20 6 R E LS DO 20 0 T K LS DO 16 0 18 3 R C THESE EXAMPLE TAKEN FROM 18 4 C A WORKING PROGRAM N 2 pa E NOT The next example further exercises the flexibility of the subroutine calling structure In this example a subroutine calls ITSELF until a certain condition is satisfied and then it begins a series of RETURNS while calculating a factorial for a number A return to itself is made for each call it made to itself the last return sends control back to the DO statement which originally called this factorial subroutine This sort of subroutine calling is known as RECURSION Computer theory buffs should note that the initial variable list is used for all levels of the calling sequence FOCAL does not dynamicall
33. ter programming Quite often however several values must be simultaneously associated with a single concept and thus the programmer would like to have a single variable name represent these many values A chess board is a good example of this since the programmer would like 64 values held for the single board While it would be possible to assign each of the squares a separate name FOCAL s subscripted variable feature allows all the squares to be referenced with the same name A variable which has many values is called an ARRAY and its separate values may he selected by means of a SUBSCRIPT or INDEX A subscript is an integer tag identifying a particular value within an array It is enclosed in parentheses immediately following the array name BD 1 for example might be the first square of the board while BD 64 might be the last Little advantage would be realized were it not for the fact that subscripts themselves can be variable names or even expressions In other words any expression can be put into the parentheses following the array name FOCAL merely calculates the value of the expression drops any fractional part and uses the resultant integer to select a single value from the array As an illustration the following sequence of statements written as a subroutine counts the number of pieces a chess bishop can threaten from his square Some initial definitions at the beginning of the program are shown as is the routine itself the ac
34. that line could have been any legal statements in the language They must be followed by a blank and the ENTIRE LINE must be followed by a semicolon In the following example 12 4 FOR II VN NN Q TYPE II FSOT II the variable II is initially given the value VN On successive loops its value increases by the amount NN and when this value exceeds Q control is passed to the next LINE NUMBER If only 2 values follow the equal sign it is assumed that the increment has been omitted leaving only the start and end values for the next II In this case the increment is set to 1 0 Since the FOR command executes only the statements on its same line it is convenient to use it in conjunction with the DO command The polynomial graphing given on this page shows this in use 20 2 S LX 40 S LY 70 S YN 0 S YX 100 20 3 S XN 0 S XX 100 20 5 S SX XX XN LX S SY YX YN LY 20 6 A DEFINE A B C FOR AX 2 BX C A B C 20 7 T GRAPH Y AX 2 BX C X IS DOWN 20 71 T Y ACROSS 20 9 F X XN SX XX DO 60 0 20 95 Q 60 1 S Y X 2 A B X C 60 3 I Y YX 60 5 S Y YX G 60 8 60 5 I YN Y 60 8 S Y YN G 60 8 60 8 T I 60 83 F J YN SY Y T 60 9 T C RETURN GO DEFINE A B C FOR AX 2 BX C 1 807 1740 PRINTS OUT GRAPH HERE The reader should study the example shown here and compare this to the fully commented version It should also be very instructive to run th
35. the first character being any letter other than F Names beginning with F are assumed to be function names FOCAL variable names are unique in their first two characters only Thus the variable names SA SAM and SAMMY refer to the same storage location LEGAL NAMES FOCAL RECOGNIZES KNOCK KN PROFIT PR COST1 co Thus COST1 and COST2 COST2 co are the same ILLEGAL NAMES REASON 3ARM First character must be be alphabetic FOOT First character must not be F To facilitate storage of large amounts of information FOCAL allows variables to be subscripted This feature will be described later 2 1 FOCAL 2 3 Evaluating Expressions FOCAL which is a contraction of FOrmula CALculator allows the user to construct arithmetic expressions or formulas using the following symbols gt EXPONENTIATION MULTIPLICATION DIVISION ADDITION SUBTRACTION x 8080 FOCAL is similar to DEC FOCAL in that the evaluation of arithmetic expressions proceeds according to standard operator priority This priority follows the table above with the operation having the highest priority Occasionally it becomes necessary due to the complexity of an expression to NEST parts of the equation in parentheses Just as a single pair of parentheses reorder the sequence of calculations in the above example the sub expression within parentheses can be reordered by separating its parts with parentheses For i
36. this state it issues an asterisk to the user s terminal It remains in this mode until the user has typed an input line followed by a carriage return In the short sequences given on the first page of the introduction the asterisks were supplied by FOCAL and the user typed the remainder of the line shown The carriage return needed at the end of every input line forces FOCAL to leave the ready mode and enter the EXECUTION mode to perform the actions specified by the input line This may mean that it only has to store the line as part of the program under construction The input line could also make FOCAL execute the input line as 1 1 FOCAL though it were a part of a program it could ask FOCAL to perform some supervisory function or it could have FOCAL execute the stored program The last mode PROGRAM INPUT occurs when FOCAL encounters and executes a special instruction ASK which will be described in full later At that time FOCAL issues a question mark to the terminal and waits as in the READY mode until the user enters a number followed by a carriage return The difference between this mode and READY is that the user is talking to his program through FOCAL The execution mode is automatically re entered after the input is completed 1 1 GO and QUIT Commands The stored program begins execution when FOCAL is given the GO command This execution begins at the lowest line number in the stored program and will proceed from there to high
37. tual calls from the main body of the program have been omitted 7 2 FOCAL 1 11 C 8 POSSIBLE DIRECTIONS OF MOVEMENT STORED IN DX DY ARRAYS 1 1 C DEFINE ARRAYS TO BE USED BY LATER SUBROUTINES 1 12 S DX 1 1 S DX 2 1 S DX 3 1 S DX 4 1 1 12 S DX 5 1 S DX 6 1 S DX 7 0 S DX 8 0 1 13 S DY 1 1 S DY 2 1 S DY 3 1 S DY 4 1 1 15 S DY 5 0 S DY 6 0 S DY 7 1 S DY 8 1 1 16 C FIRST 4 USED BY BISHOP LAST BY ROOKS ALL BY QUEEN KING K 70 02 C THIS SUBROUTINE COUNTS THE NUMBER OF OPPOSING PLAYERS 70 04 C THREATENED BY A KNIGHT AT ROW NR COLUMN NC 70 06 C ASSUMES THAT OPPOSING PIECES ARE CODED AS NUMBERS WITH 70 08 C OPPOSITE SIGNS AND THAT EMPTY SQUARES CONTAIN ZEROS 70 10 C BD HAS THE ENTIRE BOARD OF 64 SQUARES ZAP COUNTS 70 12 C THREATS FOR THE CALLING ROUTINE AND LP WILL 70 14 C BE THE LOOP DIRECTION COUNTER INTERNAL TO THIS ROUTINE 70 16 C START BY ZEROING COUNT AND STARTING DIRECTION INDEX 70 17 S ZAP 0 S LP 0 70 18 C PUT BISHIP S VALUE INTO BT TO COMPARE LATER FROM NR NC 70 20 S BT BD NC 1 B NR 70 22 C START LOOP RETURN WHEN LP PAST 4 70 24 SL P LP 1 I LP 5 70 26 RET
38. used The begins a field description of the form w 0d which describes how numbers should be printed The w is the width to be used maximum no of digits and the d is the number of these digits which are to appear after the decimal point The 0 is required In the example above note that truncation occurs if the number exceeds the field width Six digits were retained because there is room for a sign The field description remains in effect for all TYPE statements until another field description is seen The most readable output is usually made by combining text with printed values The program can thus identify a value as well as print its value The following shows this feature used in program store mode 1 1 SET G 32 SET T 5 SET D 5 G T 2 2 1 TYPE FOR ACCELERATION G AND TIME T SECONDS 2 51 TYPE AN OBJECT FALLS D FEET GO FOR ACCELERATION 32 00000 AND TIME 5 000000 SECONDS AN OBJECT FALLS 400 0000 FEET Labeling results is a very good programming practice usually ignored by beginning programmers It does require more time and effort but this is more than offset by the amount of clarity added to the code and its output For programs which could he stored for any amount of time or for lengthy programs any kind of documentation is very helpful and this labeling with TYPE statements is a very good form of docume
39. usly been assigned to lt file name gt in an OPEN statement LIB REWIND lt gt sets the cursor for file lt gt which has been assigned in an OPEN to the beginning of that file This is where the cursor is when the file is first opened LIB REWIND can be useful when chaining between programs since the second program must start at the beginning to read the data from a file LIB CLOSE lt gt removes the association between the given number and the file to which it was assigned in a previous LIB OPEN writes out the file s buffer if necessary and frees the buffer space for later use After executing a CLOSE the specified number may be re used in a LIB OPEN statement Re using a number without first closing it will result in an error LIB QUIT leaves FOCAL and returns to SOLOS CUTER Before leaving QUIT closes all files 8 5 The TRACE Feature The TRACE feature is provided to help debug stored programs It can be activated from almost anywhere in a program and can be deactivated as easily While operating trace types out each line it sees being executed by FOCAL and reports on any variable values that are changed during each line of the program A question mark is the symbol used to both activate the trace and deactivate it Any question mark encountered outside a comment statement and outside the text parts of the ASK and TYPE commands will change the trace mode If the question mark is encountered while trace is active the trac
40. y allocate new memory for copies of the variables 1 1 A N C ASK FOR THE NUMBER TO USE 1 2 S NF 1 DO 2 0 T N FACTORIAL IS NF 0 2 1 C SEE IF N IS GREATER THAN 1 IF SO SUBTRACT 2 2 C ONE AND CALL THIS ROUTINE AGAIN UNTIL IT IS 1 2 3 C THIS ROUTINE RETURNS AS MANY TIMES AS IT WAS CALLED 2 4 C AND THIS CONTROLS THE FACTORIAL CALCULATION 2 5 IF N 1 2 8 2 8 S N N 1 DO 2 0 2 6 C RETURNS ENTER HERE 2 7 S N N 1 S NE NF N 2 8 R C RETURN FROM LAST CALL 6 1 FOCAL If FOCAL runs out of step numbers for a subroutine thus threatening to continue into the next group of line numbers it issues the RETURN This makes it perfectly valid to omit the return statement from a subroutine This optimizes memory requirements at the expense of a program that becomes more difficult to read 6 2 FOCAL 7 LOOPS 7 1 The FOR Command Program loops can be constructed in FOCAL with the FOR command This command executes the remaining statements on its SAME LINE a specified number of times The number of loops depends upon the numbers given to the FOR command In its full form FOR uses 4 values an index variable a start value increment and stop value for the index These in order look like 12 1 FOR I 1 3 200 J 1 2 TYPE J In the above the values 1 3 and 200 could have been variable names and the second and third statements on
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