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Recap: numeric separators - stage 3

// Allows including “_” between numbers for readability�//�// - no runtime semantics, ignored�// - only single separator exclusively between numbers �// e.g. _1, 1_ and 1__2 not allowed as numeric separators�// �// Example:

let budget = 1_000_000_000_000; // decimals�let nibbles = 0b1010_0001_1000_0101; // binary�let message = 0xA0_B0_C0; // hex

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Recap: numeric literals extensions - stage 1

// Generalizes bigint built-in, e.g. 1236536253453n�//�// Semantics: 1234_i => �// _i(Object.freeze({string: "1234", number: 1234}))�//�// Examples:

4525_i // imaginary numbers�300_px // pixels�235435.461_m // meters

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Issue

0x123_abc

Is this a numeric separator or an extended literal?

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Alternative 1: different sigil, compatible with resolution mechanism

// two __ , e.g. 0x12_34_56__bytes

NumericLiteral __m

�Pros: works with the resolution mechanism of extensions (identifiers).�Cons: not as ergonomic?

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Alternative 2: different sigil, incompatible with current resolution

// Anything after the ` is taken as the identifier for the extension

// e.g. 0x12_34_ab`bytes, other ideas: ~, $, @, spaces

NumericLiteral `cm��Pros: more ergonomic�Cons: incompatible with the current resolution mechanism (which rely on everything following the literal to be an identifier)

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Alternate 3: Restrict Extensions to Decimals

// Only applies to decimals, disallowed in other numeric literals.

// e.g. 0x12_AB (separator), 123_px (extension), or 1_000_px (both)

DecimalLiteral _px

Pros: desirable/original syntax for extensions.�Cons: inconsistency, unavailable outside decimals.

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Alternate 4: Couple separators and extensions

Numeric Literal Separator champions couple the Numeric Literal Extension proposal and work on making them harmonious. We accept the consequence of additional labor, as well as Stage 3 -> 2 setback.��E.g. use c++’s notation for numeric separators, 1'000'000'000_px; (See annex)

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Alternative	Description	Example	Pros	Cons
Extensions: __�Separators: _	Different sigil for extensions, Same Resolution	12__px 1_000_000	Compatible with both proposals	Ergonomics of extensions
Extension: ' Separators: _	Different sigil for extensions, Different Resolution	12'px, 12 px, 12'px 1_000_000	Ergonomics of extensions	Incompatible with current resolution mechanism
Extensions: _ Separators: _	Restrict to decimal extensions	12_px	Compatible with both proposals	Inconsistency between numeric literals (e.g. 0x12_AB)
Extensions: _ Separators: '	Different sigil for numeric separators	12_px 1’000’000	Compatible with both proposals	Inconsistency with other languages, ergonomics of separators

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Alternative 1?

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Notable Background

C++ uses ` for separators and _ for extensions.

E.g. 0x123`abc.

Con:

This wasn’t C++’s preferred choice. Java, Python, Perl, Ruby, Rust, Julia, Ada, C# uses “_” for separators.
Moves separators to stage 2

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Alternative #2: candidates for extensions

Pick a different sigil:

- __, e.g. 0x123__abc� - space, e.g. 0x123 px� - $, e.g. 0x123$abc

Limit to decimals only:

E.g. 0x123_abc (separator, no extension allowed), 1_000_px (extension allowed)�

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