Context managers

[akovari]

Introduce a new type of with expression. This expression will allow accessing and manipulating local context variables within the expression in the body of the with expression.

Standard library module will be necessary to allow reading/writing context variables.

Syntax

with <expr1> (as <identifier>)?
<expr2>
end

Usecases

• transaction context
• dict/set hasher, seed

Further considerations

• the context needs to be thread-safe and work across threads whenever necessary (such as calling async)
• the distinction between builtin functions context and user library context (so that for example STM TX id cannot be overridden by the user code - either intentionally or by mistake)

[akovari]

@kurobako I'm thinking about something like this:

• I add some kind of ThreadLocal<Dict> that will hold "context variables", which will be accessible anywhere inside of the with <expr2>. The key will be the <identifier> part of the with syntax, or if not provided, then the name has to be returned as the first element of a tuple from <expr>1.

• This ThreadLocal<Dict> is set/removed in Threading.advance.

• There will be an internal and external API to access this ThreadLocal<Dict>, probably in the Context class, so that for example STMBuiltinModule can access them, or anyone implementing functions using them, such as Dict/Set can access them (like the hasher function for instance).

[akovari]

Documented in https://yatta-lang.org/docs/resource-management/