specification.md

Semantic Language Specification

For an overview about rush's syntax, please consult the grammar.

Semantics

Each rush program consists of an arbitrary amount of functions and global variables. In order to create a valid program, the main function needs to be declared.

Functions

In rush, there cannot be top-level code other than function declarations and globals.

The Main Function

The main function serves as the entry to a rush program, so that code starts executing from here. This concept is very similar to the main function in Rust or in C. The function signature of the main function has to look like this:

fn main() {
    // ...
}

Therefore the main function cannot take any arguments or return a non-unit type value.

Builtin Functions

Exit

fn exit(code: i32) -> !;

The exit function calls the operating system, demanding to quit the program with the specified exit-code.

Types

Notation	Example Value	Size	Values
int	42	64 bit	$- 2 ^{63} \le x \lt 2 ^ {63}$
float	3.1415	64 bit	IEEE float values
char	'a'	8 bit	$0 \le x \le 127$
bool	true	1 bit	true and false
() (unit)	no value	1 bit	no values

Prefix Operators

Operator	Operand Type	Produces (Type)
-	int	int
!	bool, int	same as operand

Infix Operators

Arithmetic Operators

Operator	Operand Types	Produces (Type)
+	int, char, float	same as operands
-	int, char, float	same as operands
*	int, float	same as operands
/	int, float	same as operands
%	int	int
**	int	int

Note: Division by zero using / or % is undefined behavior and may vary per backend.

Bitwise Operators

Operator	Operand Types	Produces (Type)
<<	int	int
>>	int	int
|	int, bool	same as operands
&	int, bool	same as operands
^	int, bool	same as operands

Note: Shifting by a number outside the range 0..=63 is undefined behavior and may vary per backend.

Logical Operators

Operator	Operand Types	Produces (Type)
&&	bool	bool
||	bool	bool
<	int, char, float	bool
<=	int, char, float	bool
>	int, char, float	bool
>=	int, char, float	bool
==	int, float, bool, char	bool
!=	int, float, bool, char	bool

Note: All logical infix operators require values of equal types on their left- and right-hand sides.

Type Cast

The rush language supports conversion between types. The basic syntax looks like this:

value as type

Valid Casts

From	To	Notes
int	int	redundant
int	float
int	bool	res = int != 0
int	char	defined here
float	int	truncate
float	float	redundant
float	bool	res = float != 0.0
float	char	defined here
bool	bool	redundant
bool	int	true = 1 | false = 0
bool	float
bool	char
char	char	redundant
char	int
char	float
char	bool	res = int(char) != 0

A Note on Casting to Char

When casting int or float values to char, any source value $\lt 0$ is transformed into a char with the value $0$. Furthermore, if the source value is $\gt127$, the resulting char will have the value $127$. These limitations are due to chars only containing valid ASCII characters which lie in the range $0 \le x \le 127$.