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Sep 23, 2017
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Add integer literal's grammar #108

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e560bb6
Add integer literal's grammar
brauliobz Sep 5, 2017
4de83de
Fix: digits should not include underscore
brauliobz Sep 23, 2017
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77 changes: 73 additions & 4 deletions src/tokens.md
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Expand Up @@ -216,16 +216,51 @@ literal_. The grammar for recognizing the two kinds of literals is mixed.

#### Integer literals

> **<sup>Lexer</sup>**
> INTEGER_LITERAL :
> &nbsp;&nbsp; ( DEC_LITERAL | BIN_LITERAL | OCT_LITERAL | HEX_LITERAL )
> INTEGER_SUFFIX<sup>?</sup>
>
> DEC_LITERAL :
> &nbsp;&nbsp; DEC_DIGIT (DEC_DIGIT|`_`)<sup>\*</sup>
>
> BIN_LITERAL :
> &nbsp;&nbsp; `0b` (BIN_DIGIT|`_`)<sup>\*</sup> BIN_DIGIT (BIN_DIGIT|`_`)<sup>\*</sup>
>
> OCT_LITERAL :
> &nbsp;&nbsp; `0o` (OCT_DIGIT|`_`)<sup>\*</sup> OCT_DIGIT (OCT_DIGIT|`_`)<sup>\*</sup>
>
> HEX_LITERAL :
> &nbsp;&nbsp; `0x` (HEX_DIGIT|`_`)<sup>\*</sup> HEX_DIGIT (HEX_DIGIT|`_`)<sup>\*</sup>
>
> BIN_DIGIT : [`0`-`1`]
>
> OCT_DIGIT : [`0`-`7`]
>
> DEC_DIGIT : [`0`-`9`]
>
> HEX_DIGIT : [`0`-`9` `a`-`f` `A`-`F`]
>
> INTEGER_SUFFIX :
> &nbsp;&nbsp; &nbsp;&nbsp; `u8` | `u16` | `u32` | `u64` | `usize`
> &nbsp;&nbsp; | `i8` | `u16` | `i32` | `i64` | `usize`

<!-- FIXME: separate the DECIMAL_LITERAL with no prefix or suffix (used on tuple indexing and float_literal -->
<!-- FIXME: u128 and i128 -->

An _integer literal_ has one of four forms:

* A _decimal literal_ starts with a *decimal digit* and continues with any
mixture of *decimal digits* and _underscores_.
* A _hex literal_ starts with the character sequence `U+0030` `U+0078`
(`0x`) and continues as any mixture of hex digits and underscores.
(`0x`) and continues as any mixture (with at least one digit) of hex digits
and underscores.
* An _octal literal_ starts with the character sequence `U+0030` `U+006F`
(`0o`) and continues as any mixture of octal digits and underscores.
(`0o`) and continues as any mixture (with at least one digit) of octal digits
and underscores.
* A _binary literal_ starts with the character sequence `U+0030` `U+0062`
(`0b`) and continues as any mixture of binary digits and underscores.
(`0b`) and continues as any mixture (with at least one digit) of binary digits
and underscores.

Like any literal, an integer literal may be followed (immediately,
without any spaces) by an _integer suffix_, which forcibly sets the
Expand All @@ -247,15 +282,49 @@ The type of an _unsuffixed_ integer literal is determined by type inference:
Examples of integer literals of various forms:

```rust
123; // type i32
123i32; // type i32
123u32; // type u32
123_u32; // type u32
let a: u64 = 123; // type u64

0xff; // type i32
0xff_u8; // type u8

0o70; // type i32
0o70_i16; // type i16
0b1111_1111_1001_0000_i32; // type i32

0b1111_1111_1001_0000; // type i32
0b1111_1111_1001_0000i32; // type i64
0b________1; // type i32

0usize; // type usize
```

Examples of invalid integer literals:

```rust,ignore
// invalid suffixes

0invalidSuffix;

// uses numbers of the wrong base

123AFB43;
0b0102;
0o0581;

// integers too big for their type (they overflow)

128_i8;
256_u8;

// bin, hex and octal literals must have at least one digit

0b_;
0b____;
```

Note that the Rust syntax considers `-1i8` as an application of the [unary minus
operator] to an integer literal `1i8`, rather than
a single integer literal.
Expand Down