SICP Exercise 2.55

Question

Eva Lu Ator types to the interpreter the expression

(car ''abracadabra)

To her surprise, the interpreter prints back quote. Explain.

Answer

It is useful to read the footnotes in SICP, which in this case contain the answer to the question. Footnote 100 gives us the following information:

Thus, we would type (quote a) instead of 'a, and we would type (quote (a b c)) instead of '(a b c). This is precisely how the interpreter works. The quotation mark is just a single-character abbreviation for wrapping the next complete expression with quote to form (quote ⟨expression⟩). This is important because it maintains the principle that any expression seen by the interpreter can be manipulated as a data object.

So the quotation mark is actually translated by the interpreter to quote, which is a function name. Since this is itself being quoted i.e. its string value returned, the return value is simply quote.