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## Micro2 programs
A program is a sequence of:
* function declarations
* statements
* TODO: if-else, for, for-in, etc; with no semicolon
Statements are delimited with semicolons (`;`), and are one of:
* expression (e.g. `1+2`)
* function call
* lambda definition
* variable
* variable declaration
* return statement
XXX: do we really want expressions without effects?
## Modules
A `micro2` file must start with the module name.
```
# our main module (this is a comment)
module main
```
The module name is used by the linker.
## Built-in types
### Integers
| Type | Description | Samples |
| --- | --- | --- |
| u8 | unsigned 8-bit | `123; 0xce; 0b10000;` |
| s8 | signed 8-bit | `-123;` |
| u16 | unsigned 16-bit | `65535; 0xffff;` |
| s16 | signed 16-bit | `-4096;` |
Builting functions:
| Function | Description | Samples |
| --- | --- | --- |
| hi | Get the MSB on a 16-bit number | `hi(0xaabb); # 0xaa`|
| lo | Get the LSB on a 16-bit number | `lo(0xaabb); # 0xbb`|
Type conversion is explicit:
```
var a: u8 = 10;
var b: u16 = 10;
a + b; # error: type mismatch
u16(a) + b; # 20: u16
```
### Booleans
| Type | Description | Samples |
| --- | --- | --- |
| bool | boolean | `true; false;` |
### Functions
| Type | Description | Samples |
| --- | --- | --- |
| ([params]) [-> [return]] | functions | `() { return; }` |
Functions can be defined with `def` when they have a name, or as anonymous using the lambda syntax.
```
def add(a: u8, b: u8): u8 {
return a + b;
}
add(2, 8); # 10
```
Anonymous function:
```
# increment the value passed as argument
(a: u8): u8 {
return a + 1;
}(10); # 11
```
Function are higher order functions:
```
def apply(fn: (u8) -> u8, a: u8, b: u8): u8 {
return fn(a, b);
}
apply(add, 2, 10); # 8
# using a lambda
apply((a: u8, b: u8): u8 {
return a + b;
},
2, 8); # 10
# lambdas can be assigned to variables
var double: (u8) -> u8 = (a: u8): u8 {
return a + a;
};
double(10); # 20
```
Anomymous functions can only access local variables (closures aren't supported):
```
def closure(a: u8): () -> u8 {
return (): u8 {
return a; # invalid return, undefined a
};
}
```
Functions are exported by default, unless they are defined as private:
```
# not exported (exported is the default)
private def dec(a: u8): u8 {
return a - 1;
}
```
### Special value: nil
`nil` is a reference not pointing to a value, used for example with variables with type function.
```
# fn doesn't hold a reference
var fn: (u8) -> u8 = nil;
fn(10); # runtime error
```
## Variables
Variable declaration:
```
var a: u8 = 123;
```
Group declaration:
```
var (
a: u8 = 123,
b: u16 = 1234;
);
```
Vaiables must be initialized, there are not default values.
### Constants
Constant are not variables, they don't use memory.
```
const K: u8 = 10;
```
Group declaration:
```
const (
A: u8 = 128,
B: u16 = 4096
);
```
Must be a constant expression and that can be resolved at compilation time.
```
var a: u8 = 1;
const A: u8 = a + 1; # error: unresolved value
```
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