Description: GS BASIC: Features and Editing Commands
Header: GS BASIC: Features and Editing Commands


 This article last reviewed: 15 October 1987

 ToolBox Primitives
 ------------------
 GS BASIC includes primitives (built-in, low-level commands) that let the
 user interact with the ToolBox routines. Whereas most other ToolBox routines
 are implemented in external libraries that need to be explicitly called up,
 these commands -- Eventdef, Menudef, and Taskpoll -- are included in GS BASIC
 itself because they bind the ToolBox and BASIC line numbers.

 Eventdef. The structure of Macintosh-like programs, as implemented by the
 Apple II GS and its ToolBox routines, requires that programs be event-driven.
 This means that the heart of a program is a main loop that constantly
 monitors what events -- mouse clicks, keyboard presses, window update events,
 network activity, and so on -- have taken place. Eventdef associates BASIC
 line numbers with these events: whenever one of these events occurs, GS BASIC
 starts running the instructions specified in a table set up by the programmer
 and maintained by Eventdef.

 Menudef. One of the places a mouse click can occur is in the menu bar. When
 this happens, a menu is displayed, letting the user select a menu item. The
 user specifies that a certain function is to be performed. Like Eventdef,
 Menudef associates BASIC line numbers with menu items, so that when a menu
 item is selected, GS BASIC can easily determine what statements to run, and
 run them.

 Taskpoll. Programs shouldn't start fielding events and responding to them
 until all the ToolBox libraries are loaded and the tables that Menudef and
 Eventdef maintain are initialized. The Taskpoll command lets the programmer
 turn off the interrupting feature of GS BASIC and turn them on when ready
 for them.

 Procedures and Functions
 ------------------------
 The most convenient structure of of any program is a procedure, function, or
 subroutine. In most BASICs, including Applesoft, subroutines are implemented
 in a very straightforward fashion. GS BASIC provides a more powerful way to
 specify and call procedures.

 Applesoft lets programmers call subroutines with the GOSUB xxx command, where
 xxx is the line number to which control branches. Statements are then
 executed until a RETURN command is executed, at which time the program
 returns to the line that called the subroutines, and continues from there.

 GS BASIC allows programmers to define specific procedures that are called
 with the PROC command. The PROC command performs the same functions as
 Applesoft's GOSUB, and lets the programmer pass local parameters as well.

 Editing Commands
 ----------------
 GS BASIC has a more powerful line editor than Applesoft's. Access it by
 typing EDIT linnum[-linnum]

   CONTROL-D   delete character to the left of cursor; moves line to left
   CONTROL-F   delete character under the cursor; moves line left
   CONTROL-X   delete entire line
   CONTROL-Y   delete line to left and under cursor
   CONTROL-E   toggle insert mode
   RETURN      accept entire line (even characters to right of cursor)
   DELETE      same as CONTROL-D

 GS BASIC Commands
 -----------------
 _ (underscore)  ERRLIN          LOG(            SCALB(
 ABS(            ERROR           LOG1(           SCALE(
 AND             ERRTOOL         LOG2(           SECONDS@
 ANU(            ERRTXT$(        LOGB%(          SET
 APPEND          EVENTDEF        MENUDEF         SGN(
 AS              EXCEPTION       MID$(           SHOWDIGITS
 ASC(            EXEC            MOD             SIN(
 ASSIGN          EXEVENT@(       NEGATE(         SPACE$(
 ATN(            EXFN            NEW             SPC(
 AUTO            EXP(            NEXT            SQR(
 AUXID@          EXP1(           NORMAL          SRC
 BASIC@(         EXP2(           NOT             STEP
 BDF             FILE(           NOTRACE         STOP
 BREAK           FILTYP(         OFF             STR$(
 BTN(            FILTYP=         ON              SUB$(
 CALL            FIX(            OPEN            SWAP
 CALL%           FN              OR              TAB(
 CAT             FOR             OPUTPUT         TAN(
 CATALOG         FRE             OUTREC          TASKPOLL
 CHAIN           FREMEM(         PDL(            TASKREC%(
 CHR$(           GET             PEEK(           TASKREC@(
 CLEAR           GOSUB           PERFORM         TEN(
 CLOSE           GOTO            PFX$(           TEXT
 COMPI(          GRAF            PI              TEXTPORT
 CONT            HEX$(           POKE            THEN
 CONV(           HLIST           PREFIX          TIME$
 CONV@(          HOME            PREFIX$         TIME(
 CONV#(          HPOS            PRINT           TIMER
 CONV$(          IF              PROC            TO
 CONV%(          IMAGE           PROGNAM$        TRACE
 CONV&(          INDENT          PUT             TXT
 COPY            INIT            QUIT            TYPE
 COS(            INPUT           R.STACK%(       TYP(
 CREATE          INSTR(          R.STACK@(       UBOUND(
 DATA            INT(            R.STACK&(       UCASE$(
 DATE$           INVERSE         RANDOMIZE       UIR(
 DATE(           INVOKE          READ            UNLOCK
 DEF             JOYX(           REC(            UNTIL
 DEL             JOYY(           RELATION(       UPDATE
 DELETE          KBD             REM             USING
 DIM             LEFT$(          REMDR           VAL(
 DIR             LEN(            RENAME          VAR(
 DIV             LET             REP$(           VAR$(
 DO              LIBFIND         RESTORE         VARPTR(
 EDIT            LIBRARY         RESUME          VARPTR$(
 ELSE            LIST            RETURN          VOLUMES
 END             LISTTAB         RIGHT$(         VPOS
 EOF             LOAD            RND(            WHILE
 EOFMARK(        LOCAL           ROUND(          WRITE
 ERASE           LOCATE          RUN             XOR
 ERR             LOCK            SAVE

 Toolbox Definition Files (TDFs)
 -------------------------------
 QuickDraw       ADB             Desk            Dialog
 Event           Font            Intmath         LineEdit
 List            Loader          Locater         Memory
 Menu            MiscTool        NoteSyn         Print
 QDAux           Scheduler       Scrap           StdFile
 Text            Window          Control

 Built-in Constants and Reserved Variables
 -----------------------------------------
 PI          to 20 digits
 LISTTAB     number of spaces between line number and first statement
 INDENT      controls indenting of FOR...NEXT and WHILE...UNTIL loops
 OUTREC      maximum line length
 VPOS        vertical cursor position
 HPOS        horizontal cursor position
 FRE         amount of memory available
 SHOWDIGITS  specifies the number of digits to display for REAL numbers
 KBD         holds value of last key pressed
 ERR         contains error number
 ERRLIN      contains line where error occurred

 Variable Specifications
 -----------------------
 Real:           (+ or - 1.7E38) (less than 1.5E-45 equals 0)
 Double real:    (+ or - 1.7E308) (less than 5.0E-324 equals 0)
 Integer:        (%) (2 bytes) (-32768 to 32767)
 Double integer: (@) (4 bytes) (-2147483648 to 2147483647)
 Long integer:   (&) (8 bytes) (-9223372036854775808 to 9223372036854775807)
 String:         ($) 255 characters
 Arrays:         (!)



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