dark overlord of data

Katra emulates a subset of three basic dialects: HP 2000/Access BASIC, GWBasic, and Atari Basic.

For our purposes, there is little difference between these three with the exception of string handling in GWBasic, which uses MID$, LEFT, RIGHT$, etc.

Other differences don't overlap:

You can use either braces or parens to access arrays, so DIM Z(2) and DIM Z[2] work the same.
Use Cat[alog], Gro[up], or Lib[rary] to list HP user group and system folders. Use GET-STTR1 to load from user, GET-*TREK73 to load from group, and GET-$TRADER to load from the system folder.
Use DIR to list the GWBasic root, and GWBASIC "path/to/file" to load a program.
Use FILES to list the Atari root, and ATARI "path/to/file" to load a program.

Katra specific:

Commands and keywords are not case sensitive, but variable names are. So this code:
```
                10 LET X = 10
                20 let x = 42
                30 end
                
```
will set two different variables - 'X' and 'x' to 10 and 42 respectively. ALL of the old prgrams are in upper case, and expect upper case input. I think lower case was invented in the 90's.
Use TRON and TROFF to turn trace on and off. This prints each line to the console as it executes.
Commands vs Keywords: Keywords work can be entered directly or on a line number. Commands can only be entered directly. This means that commands cannot appear in a program.
Use CTRL/C to abort a program. Use CTRL/R to restart.
When you see the '>' prompt, you are in REPL mode.
When you see the '?' prompt, a running program is waiting for input.
You can create new HP programs. They will be saved to local storage in your browser.

Append-filename: Merge basic file into workspace.
Atari "filename": Loads an atari basic game.
Catalog: List user programs.
Del [-from] [, to]: Delete program line number(s).
Execute-filename: Loads filename and executes.
Get-filename: Loads a program from storage.
Group: List group programs.
Gwbasic "filename": Loads an gw basic game.
Library: List system programs.
List [-from] [, to]: To list the program, from and to line numbers.
Purge-filename: Delete program file.
Run: Runs the currently loaded progam.
Save: Saves current program.
Scratch: Erase current variables.
Tron | Troff: Turn debug listing on or off.

Base(n): Sets the low bound array indice - default 0.
Cls: Erases the console area.
Data n, 'string', ...: List data constants.
Def FN<a>(x) = expression: Define a function.
End: Ends the program execution.
For <var> = <expression> To <expression> [Step <expression>]: Head of a For/Next loop.
Goto <line no>: Jump to the line number.
Gosub <line no>: Jump to subroutine at line number.
If <condition> Then line no: If the expression is true, jump to the line number.
Image var [,var...]: List of variables to print.
Input var [,var...]: Input a List of variables.
[Let] var = [var = ] expression: Set variable to expression.
Mat var = <Con|Zer>: Initialize array values.
Next var: Footer of for next loop. Increments var by step.
Print expression [; expression ;]: Print list of expressions.
Purge: Removes the current program from memory.
Read var [, var ...]: Read variables from Data.
Restore: Reset Data to beginning.
Return: Return from a subroutine.
Rem text...: Comments.
Stop: Stops execution.

Enter test to view the contents of the test folder. Enter get-#for to load the test program. Enter list to display the program.

Enter run to run the program, or enter exe-#data to run another test program.

Enter scr to erase the program from ry. Enter list to see that it is gone.

Enter the following code:

        10 LET X = 42
        20 PRINT "THE ANSWER IS";X
        30 END

Enter name-test and then save.

After restarting the browser, enter cat and the program 'test' will be included in the list. Enter exe-test to load and run the saved code.

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