Haskell.

This obscure language represents a peculiar corner of the programming language world called functional languages. One of the peculiar things about such languages is that they don’t have variables. Although Haskell isn’t widely known among programmers, those who know of functional languages suspect that they, too, are rather slow

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Variable means "entity that varies". But in Haskell variables are constant, you cant setf them.

First of all, "can't" is a contradiction of "cannot" and thus requires an apostrophe. If you cant even properly grammar, how can you hope to achieve intellectual clarity of ideas?

Then, to your question: in a definition \x -> x * 2 2 is a constant, because it's value cant vary between applications of the function. While the value of x most definitely can, thats why its a variable. Clearly, reading SICP by itself doesnt make make you a better programmer.