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The syntax checking routines 

This small subroutine tests whether the current character is a separator or a quote. It
returns with Zero flag set if it was a ";", "," or a """, with the first two A holds the
next character.

25A2 SEPARATOR  CP   44,","
25A4            JR   Z,#25AD,SEPAR_1     Jump if current character is a comma.
25A6            CP   59,";"
25A8            JR   Z,#25AD,SEPAR_1     Jump if it is a semicolon.
25AA            CP   34,"""
25AC            RET                      Return with Zero set if it's a quote.
25AD SEPAR_1    RST  #28,NEXT_C          Get next character.
25AE            LD   (#3DEA),A
25B1            XOR  A                   Set Zero flag.
25B2            LD   A,(#3DEA)
25B5            RET

A call is made to the 'main' ROM 'EXPT_EXP' (class-0A) subroutine, to evaluate a string
expression. During runtime, the parameters of the string (start and length) are returned
in the DE and BC register pairs.

25B6 EXPT_STR   RST  #10,CALBAS          Evaluate the string expression.
25B7            DEFW #1C8C,EXPT_EXP
25B9            RST  #30,SYNTAX_Z
25BA            RET  Z                   Return if syntax is being checked.
25BB            PUSH AF                  Save the character following the string
25BC            RST  #10,CALBAS          and the zero flag.
25BD            DEFW #2BF1,STK_FETCH     Fetch the string parameters.
25BF            POP  AF
25C0            RET

This subroutine is entered at 'MD_SYNTAX' or 'MD_SYNTAX1' depending upon whether or not
the character pointer is to be updated to the next character. A single character string
is evaluated, and its ASCII value is stored during runtime. If a separator isn't present
after the single character string, an error is given.

25C1 MD_SYNTAX  RST  #28,NEXT_C          Next character.
25C5            JR   Z,#25D9,MD_SYN2     Jump if syntax is being checked.
25C7            PUSH AF                  Save the character following the
25C8            LD   A,C                 string. A holds string length low byte.
25C9            DEC  A
25CA            OR   B                   Give an error if there isn't exactly
25CB            JP   NZ,#1658,REP_10     one character in the string.
25CE            LD   A,(DE)              Fetch the channel specifier.
25CF            RST  #10,CALBAS          Call 'ALPHA' to see if it's a valid
25D0            DEFW #2C8D,ALPHA         letter.
25D2            JP   NC,#1658,REP_10     Give error if not a valid letter.
25D5            LD   (#3E04),A           Store the specifier in the UFIA.
25D8            POP  AF                  Restore next character.
25D9 MD_SYN2    CP   59,";"
25DB            RET  Z                   Return if it's a semicolon.
25DC            CP   44,","
25DE            RET  Z                   Return if it's a comma.
25DF            JP   #1644,REP_0         Otherwise give error.

This subroutine is used to evaluate the device number.

25E2 EXPT_DEVN  AND  #DF                 Make upper case.
25E4            CP   80,"P"
25E6            JR   NZ,#25F9,EXPT_DEVN1 Jump if the device wasn't "P".
25E8            RST  #28,NEXT_C          Next character.
25E9            CALL #2611,EXPT_NUM      Get the program number.
25EC            RET  Z                   Return if syntax checking.
25ED            PUSH AF
25EE            LD   A,(#3E01)           Store program number.
25F1            LD   (#3E02),A
25F4            CALL #2604,LAST_DRV      Drive is last drive.
25F7            POP  AF
25F8            RET

Now a check is made whether the last used device is wanted.

25F9 EXPT_DEVN1 RST  #28,NEXT_C          Get next character.
25FA EXPT_DEVN2 CP   42,"*"
25FC            JR   NZ,EXPT_NUM         Jump if it wasn't a "*".
25FE            RST  #30,SYNTAX_Z
25FF            CALL NZ,#2604,LAST_DRV   Store last drive number during runtime.
2602            RST  #28,NEXT_C          Next character.
2603            RET

This subroutine is used whenever the last used drive is to be used again.

2604 LAST_DRV   LD   A,(#3DDA)           Fetch current control port status.
2607            AND  #01                 Keep only drive select.
2609            ADD  A,#01               A holds 1 for drive 2, 2 for drive 1.
260B            XOR  #03                 1 becomes 2, 2 becomes 1.
260D            LD   (#3E01),A           Store drive number.
2610            RET

This subroutine is used to evaluate a single numeric expression. The result is returned
during runtime into the BC register pair and into UFIA1.

2611 EXPT_NUM   RST  #10,CALBAS          Evaluate the expression by calling
2612            DEFW #1C82,EXPT_1NUM     'EXPT_1NUM' in the 'main' ROM.
2614            RST  #30,SYNTAX_Z
2615            RET  Z                   Return if syntax is being checked.
2616            PUSH AF
2617            RST  #10,CALBAS          Fetch the value from the calculator
2618            DEFW #1E99,FIND_INT2     stack.
261A            LD   A,C
261B            LD   (#3E01),A           Store it in UFIA1.
261E            POP  AF
261F            RET

This routine evaluates the second filename of a BASIC command. Because 'EXP_F_NAME'
stores the filename in UFIA1, both UFIAS are swapped first,
then 'EXP_F_NAME' is called and an exit is made via 'SWAP_UFIAS' to get the UFIA's in
the right place again.

2620 EXPT_2FNAM CALL #2626,SWAP_UFIAS    Swap UFIA1 and 2.
2623            CALL #2640,EXPT_FNAME    Evaluate filename.
                                         Exit via 'SWAP_UFIAS'.
This subroutine swaps the contents of UFIA1 and UFIA2 in DFCA.

2627            PUSH BC
2628            PUSH DE
2629            PUSH HL
262A            LD   B,24                An UFIA is 24 bytes long.
262C            LD   DE,#3E01            Start of UFIA1.
262F            LD   HL,#3E1A            Start of UFIA2.
2632 SWAP_LOOP  LD   A,(DE)              Exchange the contents.
2633            LD   C,(HL)
2634            EX   DE,HL
2635            LD   (DE),A
2636            LD   (HL),C
2637            INC  DE
2638            INC  HL
2639            DJNZ #2632,SWAP_LOOP     Repeat for all 24 bytes.
263B            POP  HL
263C            POP  DE
263D            POP  BC
263E            POP  AF
263F            RET

A string expression is evaluated and, provided that the length is within the range 1..10
characters, is stored in UFIA1.

2640 EXPT_FNAME CALL #25B6,EXPT_STR      Evaluate the string.
2643            RET  Z                   Return if checking syntax.
2644            PUSH AF
2645            LD   A,C
2646            OR   B
2647            JP   Z,#1654,REP_8       Give error with null string.
264A            LD   HL,10
264D            SBC  HL,BC
264F            JP   C,#1654,REP_8       Give error with string length > 10.
2652            LD   HL,#3E05            Clear the filename and the directory
2655            LD   A,11                description of UFIA1.
2657 CLR_FNAME  LD   (HL),32
2659            INC  HL
265A            DEC  A
265B            JR   NZ,#2657,CLR_FNAME  Repeat for all 11 bytes.
265D            LD   HL,#3E06            Copy the filename into UFIA1.
2660            EX   DE,HL
2661            LDIR
2663            POP  AF
2664            RET

This very important subroutine is called to evaluate the syntax of the +D 'SAVE',
'LOAD', 'MERGE' and 'VERIFY' commands. The routine is entered with CH_ADD pointing to the
command; on exit during runtime UFIA1 is filled with the proper values.

2665 EXPT_PARMS RST  #28,NEXT_C          Get next character from BASIC line.
2666            CP   32," "              Give an error with character codes
2668            JP   C,#1644,REP_0       below 32, i.e. colour codes, etc.
266B            CP   170,"SCREEN$"
266D            JP   Z,#301D,DUMP_SCR$   Jump with 'SCREEN$'.
2670            LD   (#3E04),A           Otherwise store it in DEV_TYPE1.
2673            CP   64,"@"
2675            JR   NZ,#26AE,NOT_@      Jump if not a '@'.

Now deal with @.

2677            CALL #25E2,EXPT_DEVN     Evaluate drive number.
267A            CALL #25A2,SEPARATOR
267D            JP   NZ,#1648,REP_2      Give error if no separator was found.
2680            RST  #10,CALBAS          Call 'EXPT_1NUM' to evaluate the track
2681            DEFW #1C82,EXPT_1NUM     number.
2683            CALL #25A2,SEPARATOR     Test for another separator and give an
2686            JP   NZ,#1648,REP_2      error if none found.
2689            RST  #10,CALBAS          Evaluate sector number.
268A            DEFW #1C82,EXPT_1NUM
268C            CALL #25A2,SEPARATOR     Again a separator has to be found.
268F            JP   NZ,#1648,REP_2
2692            RST  #10,CALBAS          Evaluate address.
2693            DEFW #1C82,EXPT_1NUM
2695            CALL #3148,ST_END_RAM    Confirm end of statement, and exit
                                         during syntax checking.
2698            RST  #10,CALBAS          Fetch the address from the calculator
2699            DEFW #1E99,FIND_INT2     stack.
269B            LD   (#3E15),BC          Store it in LENGTH1_2
269F            RST  #10,CALBAS          Fetch sector.
26A0            DEFW #1E99,FIND_INT2
26A2            LD   (#3E13),BC          Store it in FILE_ADDR1
26A6            RST  #10,CALBAS          Fetch track.
26A7            DEFW #1E99,_FIND_INT2
26A9            LD   (#3E11),BC          Store it in LENGTH1_1
26AD            RET                      Exit.

26AE NOT_@      CP   42,"*"              Call 'MD_SYNTAX' if it was a "*".
26B0            CALL Z,#25C1,MD_SYNTAX
26B3            CALL #25E2,EXPT_DEVN     Fetch device or program number.
26B6            CALL #25A2,SEPARATOR     Test for a separator.
26B9            PUSH AF
26BA            RST  #30,SYNTAX_Z
26BB            JR   Z,#26D6,FILENAME    Jump if syntax checking.
26BD            LD   A,(#3E04)           Fetch device descriptor.
26C0            AND  #DF                 Only capitals.
26C2            CP   68,"D"
26C4            JR   Z,#26D1,NOT_@1      Jump if device is disk.
26C6            CP   77,"M"
26C8            JR   Z,#26D1,NOT_@1      Or disk with Microdrive syntax.
26CA            CP   80,"P"
26CC            JR   Z,#26DB,PARAMS      Jump with program.
26CE            JP   NZ,#1658,REP_10     Give error with unknown device.
26D1 NOT_@1     POP  AF                  Give error if no separator or quote
26D2            JP   NZ,#1644,REP_0      found with devices "D" and "M".
26D5            PUSH AF                  Balance 'POP AF' below.
26D7            CALL Z,#2640,EXPT_FNAME  Evaluate filename if necessary.
26DA            PUSH AF                  Balance next instruction.
26DC            CP   13
26DE            JP   Z,#276F,NO_PARAMS   Jump with ENTER.
26E1            CP   58,":"
26E3            JP   Z,#276F,NO_PARAMS   Jump with colon.
26E6            CP   204,"TO"
26E8            JP   Z,#2308,TO          Jump with 'TO'.
26EB            CP   170,"SCREEN$"
26ED            JP   Z,#27A5,SCREEN$     Jump with 'SCREEN$'.
26F0            CP   175,"CODE"
26F2            JP   Z,#27C0,CODE        Jump with 'CODE'.
26F5            CP   228,"DATA"
26F7            JP   Z,#281A,DATA        Jump with 'DATA'.
26FA            CP   202,"LINE"
26FC            JP   Z,#275F,LINE        Jump with 'LINE'.
26FF            AND  #DF                 Only capitals.
2701            CP   83,"S"
2703            JR   NZ,#270F,NOT_S      Jump with other than 'S'.
2705            RST  #28,NEXT_C          Next character.
2706            CALL #3148,ST_END_RAM    Confirm end of statement and exit
                                         during syntax checking.
2709            LD   A,5                 Signal '48K Snapshot'.
270B            LD   (#3E05),A
270E            RET                      Finished.

270F NOT_S      CP   75,"K"
2711            JR   NZ,#271D,NOT_K      Jump with other than 'K'.
2713            RST  #28,NEXT_C          Next character.
2714            CALL #3148,ST_END_RAM    Confirm end of statement and exit
                                         during syntax checking.
2717            LD   A,9                 Signal '128K Snapshot'.
2719            LD   (#3E05),A
271C            RET                      Finished.

271D NOT_K      CP   88,"X"
271F            JP   NZ,#1644,REP_0      Give error with other than 'X'.
2722            RST  #28,NEXT_C          Next character.
2723            CALL #25A2,SEPARATOR     Jump if a separator found, there is
2726            JR   Z,#2736,XFILE_1     more.
2728            CALL #1635,TEST_5        There must follow a address if SAVEing.
272B            JP   NZ,#1648,REP_2      Give error if SAVEing.
272E            CALL #3148,ST_END_RAM    Confirm end of statement and exit
                                         during syntax checking.
2731            LD   BC,#3BD6            Load address of execute file.
2734            JR   #273F,XFILE_2       Jump forward.

A separator has been found, so there should follow an address.

2736 XFILE_1    RST  #10,CALBAS          Evaluate address.
2737            DEFW #1C82,EXPT_1NUM
2739            CALL #3148,ST_END_RAM    Confirm end of statement and exit
                                         during syntax checking.
273C            RST  #10,CALBAS          Fetch the address.
273D            DEFW #1E99,FIND_INT2
273F XFILE_2    LD   (#3E13),BC          Store it in FILE_ADDR1
2743            LD   BC,510              Length of execute file on double
2746            LD   A,(#3DDA)           density disks.
2749            AND  #04
274B            JR   Z,#2750,XFILE_3     Jump if double density selected.
274D            LD   BC,254              Otherwise this is the length of the
                                         execute file.
2750 XFILE_3    LD   (#3E11),BC          Store length in LENGTH1_1.
2754            LD   A,3                 File type is 'CODE'.
2756            LD   (#3E10),A           Store it in FILE_TYPE1.
2759            LD   A,11                Signal 'Execute file'.
275B            LD   (#3E05),A           Store in DIR_DESCR1
275E            RET                      Finished.

Now deal with LINE. The +D allows LOAD, VERIFY and MERGE .. LINE to be entered as a
command but the LINE is completely ignored.

275F LINE       RST  #28,NEXT_C          Advance CH_ADD.
2760            RST  #10,CALBAS          Evaluate autostart line number by
2761            DEFW #1C82,EXPT_1NUM     calling 'EXPT_1NUM' in the 'main' ROM.
2763            CALL #3148,ST_END_RAM    Confirm end of statement, and exit
                                         during syntax checking.
2766            RST  #10,CALBAS          Fetch the autostart line number.
2767            DEFW #1E99,FIND_INT2
2769            LD   (#3E17),BC          Store it in AUTOSTART1.
276D            JR   #2772,PROG

If there are no parameters, as with a BASIC program, the syntax checking ends here.

276F NO_PARAMS  CALL #3148,ST_END_RAM    Confirm end of statement, exit when
                                         syntax checking.
2772 PROG       LD   A,(#3E04)
2775            AND  #DF                 Only capitals.
2777            CP   80,"P"              Jump if the device wasn't "P", i.e. no
2779            JR   NZ,#2782,PROG_1     program number was specified.
277B            CALL #1635,TEST_5        'SAVE pn' is not supported, so give an
277E            RET  Z                   error if saving, otherwise return.
277F            JP   #1644,REP_0

2782 PROG_1     XOR  A                   File type is 'BASIC'.
2783            LD   (#3E10),A
2786            LD   A,1                 Signal 'BASIC file'.
2788            LD   (#3E05),A
278B            LD   HL,(23641)          Fetch (E_LINE), the first location past
                                         the variables area.
278E            LD   DE,(23635)          Fetch (PROG), the 'start' of the BASIC
2792            LD   (#3E13),DE          program and store it in FILE_ADDR1
2796            SCF                      Calculate ((E_LINE)-(PROG)-1), i.e. the
2797            SBC  HL,DE               length of the program and its
2799            LD   (#3E11),HL          variables. Store it in LENGTH1_1.
279C            LD   HL,(23627)          Fetch (VARS) and calculate
279F            SBC  HL,DE               (VARS)-(PROG), i.e. the length of the
                                         program without its variables.
27A1            LD   (#3E15),HL          Store it into LENGTH1_2.
27A4            RET                      Finished.

If the token is SCREEN$, the parameters are entered directly into the file header.

27A5 SCREEN$    RST  #28,NEXT_C          Get the next character.
27A6            CALL #3148,ST_END_RAM    Confirm end of statement and exit
                                         during syntax checking.
27A9            LD   HL,6912             The size of the display file is stored
27AC            LD   (#3E11),HL          into LENGTH1_1.
27AF            LD   HL,16384            The startaddress is stored into
27B2            LD   (#3E13),HL          FILE_ADDR1
27B5            LD   A,3                 File type is 'CODE'.
27B7            LD   (#3E10),A
27BA            LD   A,7                 Signal 'SCREEN$'.
27BC            LD   (#3E05),A
27BF            RET

Now deal with CODE, three parameters are needed: "start", "length" and "execute
address". With LOAD there may be none, one, two or three parameters, but with SAVE at
least two parameters must be present.

27C0 CODE       RST  #28,NEXT_C          Update CH_ADD.
27C1            CP   13                  If there are no further parameters,
27C3            JR   Z,#27C9,CODE_1      jump to use '0' as default value.
27C5            CP   58,":"              Jump if there are parameters to be
27C7            JR   NZ,#27D4,CODE_2     evaluated (i.e. the next character is
                                         not a colon).
27C9 CODE_1     CALL #1635,TEST_5        'SAVE .. CODE' has to be followed by at
27CC            JP   NZ,#1648,REP_2      least two numbers, so give an error if
                                         none present.
27CF            RST  #10,CALBAS          A call to the 'main' ROM routine
27D0            DEFW #1CE6,USE_ZERO      'USE_ZERO' is made to use a value of
27D2            JR   #27DC,CODE_3        zero as default.

It's likely that an address follows.

27D4 CODE_2     RST  #10,CALBAS          Use the 'main' ROM routine to evaluate
27D5            DEFW #1C82,EXPT_1NUM     the first parameter.
27D7            CALL #25A2,SEPARATOR
27DA            JR   Z,#27E7,CODE_4      Jump if a separator is present.
27DC CODE_3     CALL #1635,TEST_5        Give an error if there isn't a second
27DF            JP   NZ,#1648,REP_2      number with 'SAVE .. CODE'.
27E2            RST  #10,CALBAS          Otherwise use zero as default.
27E3            DEFW #1CE6,USE_ZERO
27E5            JR   #27EF,CODE_5

The length seems to be present also.

27E7 CODE_4     RST  #10,CALBAS          Evaluate the second parameter.
27E8            DEFW #1C82,EXPT_1NUM
27EA            CALL #25A2,SEPARATOR     Jump if a second separator is found.
27ED            JR   Z,#27F4,CODE_6
27EF CODE_5     RST  #10,CALBAS          Otherwise zero is default.
27F0            DEFW #1CE6,USE_ZERO
27F2            JR   #27F7,CODE_7

There's even an execute address.

27F4 CODE_6     RST  #10,CALBAS          Evaluate the third parameter.
27F5            DEFW #1C82,EXPT_1NUM
27F7 CODE_7     CALL #3148,ST_END_RAM    Confirm end of statement and exit
                                         during syntax checking.
27FA            RST  #10,CALBAS          Fetch the "autoexecute" address from
27FB            DEFW #1E99,FIND_INT2     the calculator stack and store it into
27FD            LD   (#3E17),BC          AUTOSTART1
2801            RST  #10,CALBAS          Fetch the "length".
2802            DEFW #1E99,FIND_INT2
2804            LD   (#3E11),BC          Store it into LENGTH1_1
2808            RST  #10,CALBAS          Fetch the "start".
2809            DEFW #1E99,FIND_INT2
280B            LD   (#3E13),BC          Store it into FILE_ADDR1
280E            LD   A,3                 File type is 'CODE'.
2811            LD   (#3E10),A
2814            LD   A,4                 Signal 'CODE file'.
2816            LD   (#3E05),A
2819            RET                      Finished.

Finally the routine to evaluate DATA parameters.

281A DATA       CALL #163A,TEST_6        Give an error if attempting to MERGE an
281D            JP   NZ,#1660,REP_14     array.
2820            RST  #28,NEXT_C          Next character.
2821            RST  #10,CALBAS          Call LOOK_VARS to look for the array
2822            DEFW #28B2,LOOK_VARS     name.
2824            SET  7,C
2826            JR   NC,#2833,DATA_1     Jump if handling an existing array or
                                         if syntax checking.
2828            LD   HL,#0000            Signal 'using a new array'.
282B            CALL #1630,TEST_4
282E            JR   NZ,#284E,DATA_3     Jump if LOADing the array.
2830            JP   #165A,REP_11        Otherwise give error 'Variable not
2833 DATA_1     JP   NZ,#1644,REP_0      Give error if not an array variable.

NOTE: This test fails to exclude simple strings, but the 'bug' (present in the 'main'
ROM) is corrected at #283E.

2836            RST  #30,SYNTAX_Z
2837            JR   Z,#2860,DATA_5      Jump if syntax is being checked.
2839            CALL #1635,TEST_5
283C            JR   Z,#2843,DATA_2      Jump if LOADing.
283E            BIT  7,(HL)              Give an error if trying to SAVE a
2840            JP   Z,#1644,REP_0       simple string.
2843 DATA_2     INC  HL                  Point to the 'length' of the array.
2844            LD   A,(HL)              Store the length into LENGTH1_1.
2845            LD   (#3E11),A
2848            INC  HL
2849            LD   A,(HL)
284A            LD   (#3E12),A
284D            INC  HL                  Advance to the start of the array.
284E DATA_3     LD   A,C                 Store array name into LSB of LENGTH1_2.
284F            LD   (#3E15),A
2852            LD   A,1                 File type is 'NUM ARRAY'.
2854            BIT  6,C
2856            JR   Z,#2859,DATA_4      Jump if really a numeric array.
2858            INC  A                   File type is 'STR ARRAY'.
2859 DATA_4     LD   (#3E10),A           Store file type into FILE_TYPE1.
285C            INC  A                   Signal: (A=2) 'Numeric array',
285D            LD   (#3E05),A           (A=3) 'String array'.
2860 DATA_5     EX   DE,HL               DE holds 'start' of the array (or #0000
                                         with a 'new' array to be LOADed).
2861            RST  #28,NEXT_C          Next character.
2862            CP   41,")"              Check that the ')' does exist.
2864            JP   NZ,#1648,REP_2      Report an error if not.
2867            RST  #28,NEXT_C          Next character.
2868            CALL #3148,ST_END_RAM    Confirm end of statement and exit
                                         during syntax checking.
286B            LD   (#3E13),DE          Store "start" of the array into
286F            RET                      FILE_ADDR1 and exit.

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