Add lambdas with statements / local functions in imp syntax #562
Description
Currently, in imp syntax there is no way of writing lambdas that have statements in them.
We can raise them to proper top-level functions, but then any captured variables must be passed through additional arguments, which increases the overhead.
But the main problem is that it's very inconvenient to do so. Instead we'd like a way to write lambdas with statements like we can do in Fun syntax.
I'll propose two possible syntaxes here.
def foo:
lambda x:
...
return y
return z
Here lambda x defines a block for a local anonymous function bound to variable x.
I thought of this as just a simple lambda/closure, that can freely capture variables and doesn't get lifted into a separate definition.
Another option is
def foo:
def foo/local(a, b):
...
return c
return foo/local(x, y)
This defines a function that is raised as a top-level. Captured variables are passed as arguments implicitly through a use term, like this
def foo:
use foo/local = foo__local_foo/local(captured1, captured2)
...
return foo/local(x, y)
This allow local functions to be recursive, but adds an overhead compared to just a simple lambda. And if the lambda is affine, it will get floated anyway.
I don't know which is better, need to think more about it.
I think we don't need both syntaxes, but that could also be an option.
Also, note that either syntax could have either of the described behaviours, I just think that they sort of imply intuitively the behaviours i described.