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Language evolution overview proposal #2

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Language evolution overview proposal
nikic Feb 14, 2020
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Add string interpolation as an example of a lexer change
nikic Feb 18, 2020
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Fix link
nikic Feb 18, 2020
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Clarify that "supported forever" only applies to Rust
nikic Feb 18, 2020
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Fix typo
nikic Feb 19, 2020
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Replace dot-file with underscore-file
nikic Feb 19, 2020
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Mention new file extension possibility
nikic Feb 19, 2020
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Add string interpolation as an example of a lexer change
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nikic committed Feb 18, 2020
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6 changes: 6 additions & 0 deletions rfcs/0000-language-evolution.md
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Expand Up @@ -50,6 +50,12 @@ This RFC is interesting in that it not only adds new errors, but also changes be

A [`function_and_const_lookup='global'`](https://wiki.php.net/rfc/use_global_elements) declare has been proposed and declined recently. While this particular proposal was declined, we may still wish to consider other name resolution changes that bring the rules for functions/constants and classes in line.

## String interpolation changes

The [arbitrary expression interpolation](https://wiki.php.net/rfc/arbitrary_expression_interpolation) RFC proposes to introduce the `"foo #{1 + 1} bar"` syntax for interpolating arbitrary expressions. This poses a minor backwards-compatibility break, because currently `#{}` is allowed inside strings and does not have special meaning. A backwards-compatibility break could be avoided by making the syntax opt-in. It would even be possible to use the `"foo {1 + 1} bar"` syntax, though whether that is a good idea is a different question.

This example is interesting, because it involves a change to the PHP lexer, while all the previous examples involved changes to the compiler or runtime.

# Approaches

Three general approaches (more in terms of philosophy than technical detail) have been discussed in the past and are summarized here.
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