In Racket, say you're given this:
'( 'blah 'foo a)
and a is not defined. If you're iterating through the list, how can you test whether the element is a 'symbol (like blah or foo) or if it's an unbound variable, like a?

Question

In Racket, say you're given this:
'( 'blah 'foo a)
and a is not defined. If you're iterating through the list, how can you test whether the element is a 'symbol (like blah or foo) or if it's an unbound variable, like a?

anonymous · Answer

What I'm trying to do is write a list of differentiation rules that uses patterns. So an input matching the pattern '( ('ddx ('plus u v))), where u an v are pattern variables, should be translated to '( ('plus ('ddx u) ('ddx v))). But my "translator" will need to know that 'plus is just a symbol, while u and v are pattern variables.

anonymous · Answer

What about  `(symbol?`  ` )`

anonymous · Answer

The pattern variables won't be symbols, correct?