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What is the difference between ~> and ->

howardhaoracle

Hi.. 

Please explain the difference between using ~> and ->  ?? When do you use ~>  or ->?

I looked at some Skill codes and I see both are used

 Thanks for your explanation..

Howard

 

Parents

  • What Lawrence says is not strictly correct. Actually you can use the -> and ~> interchangeably except on lists, where they behave differently. With a list, if you use -> then you are treating the list as a disembodied property list where you have a list with a dummy value first (often nil) followed by key/value pairs where the key is a symbol. So for example:

    dpl=list(nil)
    dpl->colour="red"
    dpl->shape="circle"

    then:

     > dpl
    (nil shape "circle" colour "red")
    > dpl->shape
    "circle"
    > dpl->shape="square"
    "square"
    > dpl->shape
    "square"
    > dpl
    (nil shape "square" colour "red")

    If you use ~> on a list, then it effectively does a foreach mapcar over the list, applying the ~> operator on each member of the list and returning a list of the results. This is as Lawrence mentioned above. So doing:

    cv~>nets~>name

    is like doing:

    foreach(mapcar net cv~>nets net~>name)

    but obviously shorter and more to the point.

    So ~> can be used for windows, menu structures, form structures, tables and so on - just not disembodied property lists.

    Regards (and sorry to be pedantic!),

    Andrew.

Reply

  • What Lawrence says is not strictly correct. Actually you can use the -> and ~> interchangeably except on lists, where they behave differently. With a list, if you use -> then you are treating the list as a disembodied property list where you have a list with a dummy value first (often nil) followed by key/value pairs where the key is a symbol. So for example:

    dpl=list(nil)
    dpl->colour="red"
    dpl->shape="circle"

    then:

     > dpl
    (nil shape "circle" colour "red")
    > dpl->shape
    "circle"
    > dpl->shape="square"
    "square"
    > dpl->shape
    "square"
    > dpl
    (nil shape "square" colour "red")

    If you use ~> on a list, then it effectively does a foreach mapcar over the list, applying the ~> operator on each member of the list and returning a list of the results. This is as Lawrence mentioned above. So doing:

    cv~>nets~>name

    is like doing:

    foreach(mapcar net cv~>nets net~>name)

    but obviously shorter and more to the point.

    So ~> can be used for windows, menu structures, form structures, tables and so on - just not disembodied property lists.

    Regards (and sorry to be pedantic!),

    Andrew.

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