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Why is this legal (rocket) scheme?

I was going through htdp and found this somewhere in the beginning: -

Explain why the following sentences are illegal definitions: 1. (define (f 'x) x)

However, it works fine in a racket:

> (define (f 'x) x)
> (f 'a)
3
> (define a 5)
> (f a)
3

Obviously I'm missing something ... what exactly?

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2 answers


Short answer: you shouldn't use the full "#lang racket" language. Languages ​​of instruction eliminate the potentially confusing additional capabilities of the language you encounter.

In this case, your definition is interpreted as a function named f with an optional argument called quotation, which defaults to "x".



Set your language level to Beginner Learner and you will get a much smarter answer.

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This line does not work for me in the Racket: (define (f 'x) x)

. An error is reported define: not an identifier for procedure argument in: (quote x)

.



What language are you using? have you tried to run the above line in the interaction window?

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