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case statement to catch multiple symbols?

caver456

How should the list clause of a case statement clause be structured so that it matches on any one of a set of symbols?

Example:

case(a
   ('a println("A"))
   ('b println("B"))
   (('c 'd) println("C or D"))
)

a='a  --> the above code prints "A"

a='b  --> the above code prints "B"

a='c'  --> nothing is printed

a='d'  --> nothing is printed

Changing it to match on strings instead of symbols:

case(a
   ("a" println("A"))
   ("b" println("B"))
   (("c" "d") println("C or D"))
)

a="a"  --> the above code prints "A"

a="b"  --> the above code prints "B"

a="c"  --> the above code prints "C or D"

a="d"  --> the above code prints "C or D"

Basically I'd like to mimic the string behavior above, but the variable being tested is a symbol.  What's the proper way to structure the ('c or 'd) clause in this case?

Parents

  • Hi,

    Your mistake, I think, is in including the ' quote before the items, it's not needed as the case statement compares a value/variable against fixed literal target values. From the docs: "Keys are always treated as constants and are never evaluated."  Here's a cut down example based on yours:

    a = 'c => c
case(a (a "A") (b "B") ((c d) "C or D") (t "SomethingElse")) => "C or D"
a ='a => a
case(a (a "A") (b "B") ((c d) "C or D") (t "SomethingElse")) => "A"
a='f => f
case(a (a "A") (b "B") ((c d) "C or D") (t "SomethingElse")) => "SomethingElse"
a='d => d
caseq(a (a "A") (b "B") ((c d) "C or D") (t "SomethingElse")) => "C or D"

    In the symbol situation (I was going to say 'case' but ...) you can use 'caseq' as it can use 'eq' for the equality test rather than 'equal' - 'eq' is a little more efficient if you are working with symbols (just beware that 'eq' can return nil when comparing values that you think are the same but they are not 'pointing to the same object').

    Hopefully this helps you.

    Best regards,

    Lawrence.

Reply

  • Hi,

    Your mistake, I think, is in including the ' quote before the items, it's not needed as the case statement compares a value/variable against fixed literal target values. From the docs: "Keys are always treated as constants and are never evaluated."  Here's a cut down example based on yours:

    a = 'c => c
case(a (a "A") (b "B") ((c d) "C or D") (t "SomethingElse")) => "C or D"
a ='a => a
case(a (a "A") (b "B") ((c d) "C or D") (t "SomethingElse")) => "A"
a='f => f
case(a (a "A") (b "B") ((c d) "C or D") (t "SomethingElse")) => "SomethingElse"
a='d => d
caseq(a (a "A") (b "B") ((c d) "C or D") (t "SomethingElse")) => "C or D"

    In the symbol situation (I was going to say 'case' but ...) you can use 'caseq' as it can use 'eq' for the equality test rather than 'equal' - 'eq' is a little more efficient if you are working with symbols (just beware that 'eq' can return nil when comparing values that you think are the same but they are not 'pointing to the same object').

    Hopefully this helps you.

    Best regards,

    Lawrence.

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