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Comment by gagege | Hacker News Reader

I'm no language designer either, but I would guess that since Crystal wants to be 100% type inferred, they feel that having to type "var" or "let" is just boilerplate.

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Even in type inferred languages they serve some use, namely in avoiding mis-typed variable names. Languages which require "var" make a distinction between the intent of declaring a new variable vs setting the value of an existing variable, and so are able to catch instances where the programmer tries to set a non-existent variable.

Or more tersely use := and = to distinguish them.

That has nothing to do with the scoping. There's no way to know whether "left = right" means "Set 'left' to 'right'" or "Create a new variable 'left', with value 'right'".

How are they different? Both produce the same end result, Python manages this syntax just fine.

"Just fine" is papering over the fact that people get tripped up by this in Python all the time – sometimes you need to use the `global` or `nonlocal` statements to resolve the ambiguity.

https://docs.python.org/3/reference/simple_stmts.html#global

https://docs.python.org/3/reference/simple_stmts.html#nonloc...

Classic example: http://stackoverflow.com/questions/9264763/unboundlocalerror...

If you search for UnboundLocalError on StackOverflow, there are 918 results. Not all of them are due to this particular scoping ambiguity, but many of them are.

It's a mistake even in Python. It makes typos harder to catch. And a visible distinction between variables that change and values that don't makes code much easier to reason about.

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