Hi all,
Reading the documentation on ~datum in syntax/parse, I see:
The ~datum
<file:///usr/local/racket/doc/syntax/stxparse-patterns.html?q=syntax-case#%28form._%28%28lib._syntax%2Fparse..rkt%29._~7edatum%29%29>
form is useful for recognizing identifiers symbolically, in contrast to the
~literal
<file:///usr/local/racket/doc/syntax/stxparse-patterns.html?q=syntax-case#%28form._%28%28lib._syntax%2Fparse..rkt%29._~7eliteral%29%29>
form, which recognizes them by binding.
That makes sense to me. But then I see:
> (syntax-parse
> <file:///usr/local/racket/doc/syntax/Parsing_Syntax.html?q=syntax-case#%28form._%28%28lib._syntax%2Fparse..rkt%29._syntax-parse%29%29>
> (let
> <applewebdata://EC850F88-0C7E-4179-B1EF-C18D24819433/reference/let.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._let%29%29>
> ([define
> <applewebdata://EC850F88-0C7E-4179-B1EF-C18D24819433/reference/define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29>
> 'something-else]) #'(define
> <applewebdata://EC850F88-0C7E-4179-B1EF-C18D24819433/reference/define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29>
> x y))
[((~datum
<file:///usr/local/racket/doc/syntax/stxparse-patterns.html?q=syntax-case#%28form._%28%28lib._syntax%2Fparse..rkt%29._~7edatum%29%29>
define
<applewebdata://EC850F88-0C7E-4179-B1EF-C18D24819433/reference/define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29>)
var:id e:expr) 'yes]
[_
<applewebdata://EC850F88-0C7E-4179-B1EF-C18D24819433/reference/stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29.__%29%29>
'no])
'yes
> (syntax-parse
> <file:///usr/local/racket/doc/syntax/Parsing_Syntax.html?q=syntax-case#%28form._%28%28lib._syntax%2Fparse..rkt%29._syntax-parse%29%29>
> (let
> <applewebdata://EC850F88-0C7E-4179-B1EF-C18D24819433/reference/let.html#%28form._%28%28lib._racket%2Fprivate%2Fletstx-scheme..rkt%29._let%29%29>
> ([define
> <applewebdata://EC850F88-0C7E-4179-B1EF-C18D24819433/reference/define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29>
> 'something-else]) #'(define
> <applewebdata://EC850F88-0C7E-4179-B1EF-C18D24819433/reference/define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29>
> x y))
[((~literal
<file:///usr/local/racket/doc/syntax/stxparse-patterns.html?q=syntax-case#%28form._%28%28lib._syntax%2Fparse..rkt%29._~7eliteral%29%29>
define
<applewebdata://EC850F88-0C7E-4179-B1EF-C18D24819433/reference/define.html#%28form._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._define%29%29>)
var:id e:expr) 'yes]
[_
<applewebdata://EC850F88-0C7E-4179-B1EF-C18D24819433/reference/stx-patterns.html#%28form._%28%28lib._racket%2Fprivate%2Fstxcase-scheme..rkt%29.__%29%29>
'no])
'yes
I’m confused by this. It seems, based on the first sentence I quoted, that in
the second example, in which the syntax being parsed has define bound to
something other than the usual, the use of ~literal should make the first
clause fail to match. And I’d have expected the examples to contrast ~datum and
~literal, rather than exhibit the same behavior.
Could someone please explain this to me?
Thanks,
Jordan
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