Lexical Elements

digit  ::= ['0'-'9']
digit_ ::= digit | '_'
hex_digit  ::= digit | ['a'-'f''A'-'F']
hex_digit  ::= hex_digit | '_'

Identifiers

identifier ::= nondigit (nondigit | digit)*
nondigit   ::= ['_''a'-'z''A'-'Z']

Keywords

Some identifiers are reserved keywords which have a special meaning in an Impala program:

as else enum extern fn for if impl in let mut static struct trait type while with
true false
bool int uint float double
i8 i16 i32 i64
u8 u16 u32 u64
f16 f32 f64

Furthermore, return, continue and break play a special role although they are technically not keywords.

See

[[Function Item]]
[[If Expression]]
[[For Expression]]
[[Function Expression]]
[[While Expression]]

Punctators

This tokens have a special meaning depending on the context they occur in:

[ ] ( ) { } . ->
++ -- & * + - ~ !
/ % << >> < > <= >=
== != ^ | && || 
? : ; ...
= *= /= %= += -= <<= >>= &= ^= |=
, # ##

Literals

Note that you can use underscores to group your integer and float literals.

literal ::= int_literal
          | float_literal
          | char_literal
          | str_literal

Integer Literals

int_literal ::= digit digit_* int_suffix
              | binary_int int_suffix
              | octal_int int_suffix
              | hex_int int_suffix

binary_int ::= '0b' digit_*
octal_int  ::= '0o' digit_*
hex_int    ::= '0x' hex_digit_*

int_suffix ::= /*empty*/
             | 'i' | 'i8' | 'i16' | 'i32' | 'i64'
             | 'u' | 'u8' | 'u16' | 'u32' | 'u64'

Float Literals

float_literal ::= digit digit_* '.' digit_* float_suffix
                | digit digit_* '.' digit_* ['e''E'] digit_* float_suffix
                | hex_float

hex_float     ::= '0x' hex_digit_* '.' digit_* ['p''P'] digit_* float_suffix

float_suffix  ::= /*empty*/
                | 'h' | 'f' | 'f16' | 'f32' | 'f64'

Char Literals

String Literals

Examples

fn main() -> () {
    { let u: u32  = 42u; }
    { let i: i8  = 0i8; }
    { let i: i16 = 0i16; }
    { let i: i32 = 0i32; }
    { let i: i64 = 0i64; }
    { let i: u8  = 0u8; }
    { let i: u16 = 0u16; }
    { let i: u32 = 0u32; }
    { let i: u64 = 0u64; }
    { let f: f32 = 0f32; }
    { let f: f64 = 0f64; }
    { let i: i32 = 0b01; }
    { let i: i32 = 0b0_1111; }
    { let i: i32 = 0b01_; }
    { let i: i32 = 0b01; }
    { let i: i32 = 0o0_1234567; }
    { let i: i32 = 0o01234567_; }
    { let i: i32 = 0x0_123456789abcdef; }
    { let i: i32 = 0x0123456789abcdef_; }
    { let f: f64 = 1e1; }
    { let f: f64 = 1e-1; }
    { let f: f64 = 1e+1; }
    { let f: f64 = 1.7e1; }
    { let f: f64 = 1.8e-1; }
    { let f: f64 = 1.9e+1; }
    { let f: f64 = 1.7e_4; }
    { let f: f64 = 1.8e-_5; }
    { let f: f64 = 1.9e+_6; }
    { let f: f64 = 1.1_2_3_; }
    { let f: f32 = 1.1_2_3_f32; }
    { let f: f32 = 1.1_2_3_e+16f; }
}