Andrew Kesterson
cdaefcc941
Organised the way the C128 Programmer's Reference Guide is: the language first, then each hardware area, then the reference sections. One markdown file per chapter. The verb and function references are generated from the interpreter's own dispatch table, with an assertion that every row is described, so they cannot drift out of step with what the program accepts. 98 verbs and 30 functions. Every example was run before it was written down, which caught three claims that were wrong: a whole FOR loop on one line prints nothing rather than looping once, MID and INSTR count from zero where a C128 counts from one, and a multi-line DEF returns a value the caller has to assign away. Chapter 13 is the list a BASIC 7.0 programmer needs -- roughly sixty documented differences, including the two known FOR defects and the fact that drawing does not survive a frame. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
2.4 KiB
2. Getting started
The prompt
Run basic with no arguments and you get a prompt:
$ ./build/basic
READY
READY is printed whenever the interpreter is waiting for you, which is at startup
and after a program stops.
Anything you type with a line number is stored as part of a program. Anything you type without one runs immediately:
PRINT 2 + 2
4
READY
Your first program
10 PRINT "WHAT IS YOUR NAME"
20 INPUT "> " N$
30 PRINT "HELLO, " + N$
RUN
Type LIST to see it back, RUN to run it again, and NEW to throw it away.
Line numbers
Lines are stored under their numbers and run in numeric order, so the gaps are what let you insert later:
10 PRINT "FIRST"
30 PRINT "THIRD"
20 PRINT "SECOND"
LIST
10 PRINT "FIRST"
20 PRINT "SECOND"
30 PRINT "THIRD"
Typing a line number with nothing after it deletes that line. DELETE 20-40 removes a
range, and RENUMBER tidies the whole program up — it rewrites every GOTO and
GOSUB to match, so it will not break your branches.
AUTO 10 turns on automatic numbering so you do not have to type them; AUTO 0 turns
it off again.
Several statements on one line
Statements are separated by colons:
10 A# = 1 : B# = 2 : PRINT A# + B#
There is one important limit: block structures do not work inside a single line.
10 FOR I# = 1 TO 3 : PRINT I# : NEXT I#
prints nothing at all. The loop body is skipped entirely, because the interpreter skips
forward a line at a time looking for the NEXT and never finds one on the line it is
already past. Write loops across several lines:
10 FOR I# = 1 TO 3
20 PRINT I#
30 NEXT I#
The same applies to DO/LOOP.
Running a file
$ ./build/basic program.bas
The file is read, stored, and run. It is exactly the same as typing the program in and saving yourself the trouble.
You can also pipe a program in:
$ echo '10 PRINT "HI"
RUN' | ./build/basic
Saving and loading
DSAVE "myprogram.bas"
DLOAD "myprogram.bas"
SAVE and LOAD are the same verbs under their other names. VERIFY "myprogram.bas"
compares what is in memory against the file and prints OK if they match.
Stopping
QUIT ends the interpreter. STOP stops a program and returns you to the prompt,
where CONT resumes it from where it stopped. END also stops the program, but does
not arm CONT.
In the SDL build, closing the window stops the program too.