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https://github.com/nanoflite/basic
:tv: A from-scratch BASIC interpreter with a focus on being easy to extend and port.
https://github.com/nanoflite/basic
basic c interpreter
Last synced: 2 months ago
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:tv: A from-scratch BASIC interpreter with a focus on being easy to extend and port.
- Host: GitHub
- URL: https://github.com/nanoflite/basic
- Owner: nanoflite
- License: mit
- Created: 2016-02-22T18:54:30.000Z (almost 9 years ago)
- Default Branch: develop
- Last Pushed: 2023-05-06T10:36:50.000Z (over 1 year ago)
- Last Synced: 2024-07-12T04:37:19.222Z (7 months ago)
- Topics: basic, c, interpreter
- Language: C
- Homepage:
- Size: 380 KB
- Stars: 84
- Watchers: 8
- Forks: 26
- Open Issues: 4
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
- AwesomeInterpreter - basic
README
A from-scratch BASIC interpreter with a focus on being easy to extend and port.
[](https://asciinema.org/a/37018)
# Introduction
This is a BASIC interpreter written from scratch in C. For the moment two architectures are supported, POSIX and AVR XMega via the avr-gcc toolchain.
Most of the common BASIC keywords are supported:
* PRINT expression-list [ ; ]
* IF relation-expression THEN statement
* GOTO expression
* INPUT variable-list
* LET variable = expression
* GOSUB expression
* RETURN
* FOR numeric\_variable '=' numeric\_expression TO numeric_expression [ STEP number ]
* CLEAR, NEW
* LIST
* RUN
* END
* DIM variable "(" expression ")"
* ABS, AND, ATN, COS, EXP, INT, LOG, NOT, OR, RND, SGN, SIN, SQR, TAN
* LEN, CHR$, MID$, LEFT$, RIGHT$, ASC
# Extend
It should be easy to register a new BASIC function, as shown here with a `sleep` function for the XMEGA.
```C
register_function_1(basic_function_type_keyword, "SLEEP", do_sleep, kind_numeric);
...
int do_sleep(basic_type* delay, basic_type* rv)
{
delay_ms(delay->value.number);
rv->kind = kind_numeric;
rv->value.number = 0;
return 0;
}
```
Let's use that new keyword.
```REALbasic
10 INPUT "YOUR NAME?", NAME$
20 CLS
30 FOR I=1 TO LEN(NAME$)
40 PRINT MID$(NAME$,I,1);
50 SLEEP(500)
60 NEXT
70 PRINT
```
# Port
It should be easy to port the interpreter to other architectures. As an example there is a port to an XMega 128A4U included using the [Batsocks breadmate board](http://www.batsocks.co.uk/products/BreadMate/XMega%20PDI%20AV.htm).
# Use
There is a simple REPL for the BASIC interpreter. You can use it in an interactive way, just as you would do on a 80's era computer.
```
_ _
| |__ __ _ ___(_) ___
| '_ \ / _` / __| |/ __|
| |_) | (_| \__ \ | (__
|_.__/ \__,_|___/_|\___|
(c) 2015-2016 Johan Van den Brande
10 PRINT "HELLO"
20 GOTO 10
```
You can give it a BASIC file on the command line.
```
$> basic examples/diamond.bas
*
***
*****
*******
*********
***********
*************
***************
*****************
***************
*************
***********
*********
*******
*****
***
*
```
You can also use the shebang operator to make standalone BASIC scripts
```
#!/usr/bin/env basic
10 RADIUS=10
20 FOR I=1 TO RADIUS-1
30 W=INT(RADIUS*SIN(180/RADIUS*I*3.1415/180))
40 PRINT SPC(RADIUS-W);:FOR J=1 TO 2*W:PRINT "*";:NEXT J:PRINT
50 NEXT I
```
```
$> ./examples/circle.bas
******
**********
****************
******************
********************
******************
****************
**********
******
```
It is easy to embed the interpreter into your own application.
```C
basic_init(2048, 512); // memory size, stack size
basic_register_io(putchar, getchar);
basic_eval("10 PRINT \"HELLO\"");
basic_eval("RUN");
basic_destroy();
```
On OSX/POSIX you can use the 'BASIC\_PATH' environment variable to set the folder used for loading and saving BASIC programs. The 'BASIC\_PATH' defaults to '.'.
BASIC programs are expected to end with '.bas'. You can use LOAD, SAVE, DELETE and DIR.
# Copyright
(c) 2015 - 2016 Johan Van den Brande