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LibJS+js: Support getting last value from "_" variable

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The interpreter now has an "underscore is last value" flag, which makes
Interpreter::get_variable() return the last value if:

- The m_underscore_is_last_value flag is enabled
- The name of the variable lookup is "_"
- The result of that lookup is an empty value

That means "_" can still be used as a regular variable and will stop
doing its magic once anything is assigned to it.

Example REPL session:

> 1
1
> _ + _
2
> _ + _
4
> _ = "foo"
"foo"
> 1
1
> _
"foo"
> delete _
true
> 1
1
> _
1
>
This commit is contained in:
Linus Groh 2020-06-08 12:08:35 +01:00 • committed by Andreas Kling
parent 89004a3a40
commit 5072d4e02d
Notes: sideshowbarker 2024-07-19 05:44:54 +09:00
3 changed files with 13 additions and 2 deletions
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9
Libraries/LibJS/Interpreter.cpp
View file

@ -70,7 +70,9 @@ Value Interpreter::run(const Statement& statement, ArgumentVector arguments, Sco
auto& block = static_cast<const ScopeNode&>(statement);
enter_scope(block, move(arguments), scope_type);
m_last_value = js_undefined();
if (block.children().is_empty())
m_last_value = js_undefined();
for (auto& node : block.children()) {
m_last_value = node.execute(*this);
if (should_unwind()) {
@ -176,7 +178,10 @@ Value Interpreter::get_variable(const FlyString& name)
return possible_match.value().value;
}
}
return global_object().get(name);
auto value = global_object().get(name);
if (m_underscore_is_last_value && name == "_" && value.is_empty())
return m_last_value;
return value;
}
Reference Interpreter::get_reference(const FlyString& name)