# xBASIC

xBASIC is designed to be a very simple language. The goal of this library is to make it easy to add
user-defined logic to your Rust project.

Features:

- Gracefully handles bad or malicious code.
- Allows setting a compute time limit. 
- Allows calling xBASIC functions from Rust
- Allows calling Rust functions from xBASIC
- Allows defining custom IO, which `PRINT` and `INPUT` work with
- Entirely safe rust

TODO:

- Arrays
- Better standard library(string lengths, type conversions, etc)

A basic interpreter is also included in this project. It can be started with `cargo run`. It possesses a REPL, but can also run files.

## Syntax

As mentioned already, xBASIC is a very simple language. Like other BASIC languages, it is designed to be easy
for beginners to understand.

### Printing

```
print "hello world" // "hello world"
print "hello" "world" // "hello world"
print 5 "+" 3 "=" 5 + 3 // "5 + 3 = 8"
```

`PRINT` will automatically concatenate multiple expressions together.

### Reading

```
input a // Read in a line, store it in a
input b // Read in another line, store it in b
```

### Variables

```
a = 3
print a // "3"
print b // "0"
```

All variables are implicitly initialized to 0.

### Comparisons

```
a = 3
print a = 3 // "true"
print not a = 3 // \"false\"
print a < 3 // "false"
print a > 3 // "false"
print a <= 3 // "true"
print a >= 3 // "true"
```

Note that `a = 3` is an assignment when used as a statement, and a comparison when used as an expression.

### IF statements

```
if 3 = 3 then
    print "hello world" // runs
end if

if not a then
    print "hello world" // runs, because a is implicitly 0
end if

if b = 2 then
elseif b = 3 then
elseif b = 4 then
else
end if
```

Truthy values are `true` and all numbers other than 0. It is an error to attempt to evaluate the truthiness of a string.

### WHILE statements
```
a = 0
while a < 10
    print a // prints 0 1 2 3 4 5 6 7 8 9, each on a newline
    a += 1
wend
```

### FOR statements
```
for x = 10 to 20
    print x // prints 10 11 12 13 14 15 16 17 18 19 20, each on a newline
next x
```

### Functions

```
print a("hello", "world") // "helloworld"

function a(b, c)
    return b + c
end function
```

Functions can be defined before or after they are called. Return values can be specified with `return`,
otherwise they will implicitly return 0. Recursion is also allowed.

For more examples, check out the `examples` directory.