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But stack languages generally do evaluate left to right.

I don't see why you couldn't do right to left. Makes no semantic difference.

But the original post has a snippet that should not only be evaluated right to left, but also bottom to top. Unless their indentation implies hidden parens.

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Yeah, I mean right-to-left, in response to the question the article asks: Why have I never seen... ...a stack language that evaluates right-to-left?

it's because the tokens are evaluated in the order they are consumed by the parser. But now that I think about it, the tokens only look left-to-right because that's how the text is displayed. So what's really happening is that tokens are evaluated in FIFO, and there's no reason the tokens for (a b +) couldn't be written as (+ b a).

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