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Comment by amyjess | Hacker News Reader

> foo.on_click(lambda: x += 1)

Mutation in lambdas is not compatible with your complaint about "inadequate support for high-level functional programming", as it goes against the principles of FP.

You can't do that in Haskell either, and any FP purist would blanch at a statement like that.

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> You can't do that in Haskell either, and any FP purist

What about us FP pragmatists? Also in some domains I'd argue being a FP purist is the most pragmatic option.

>You can't do that in Haskell either, and any FP purist would blanch at a statement like that.

Obviously you've never met State and/or lens then.

Yes, you can do it -- and no, I never said it should follow pure FP principles.

But if you write a State equivalent of "x += 1" in Python then you can use it in a lambda too.

Are you saying that a non-mutating variant of the above works? For instance:

   foo.on_click(lambda:x func(x, whatever))

yeah, except that the syntax is

  lambda x: func(x, whatever)

In fact, if x is an object that stores a mutable numeric cell, you could even do a mutating:

  lambda x: x.add(1)

Mutation isn't prohibited in Python lambdas, statements (including assignments, which are statements rather than expressions in Python), however, are.

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