Re: [Factor-talk] Way to check if a mutated element of an array is also a member?

[John B. <mr...@gm...>]

You can curry the sequence into the filter expression (using the fry vocab):

    dup '[ reverse _ member? ] filter

Or, more traditional curry:

    dup [ [ reverse ] dip member? ] curry filter

Or, you can leave it "under" the stack and access it using stack shufflers:

    dup [ reverse over member? ] filter nip

Part of your problem is that "dup reverse swap filter?" isn't doing what
you expect.

To help diagnose those kind of problems you can set a breakpoint like this
(using B):

    dup [ B dup reverse swap member? ] filter

Then you'll can see what inputs the quotation is getting on the stack.










On Tue, Mar 22, 2016 at 10:37 AM, cat stevens <the...@gm...>
wrote:

> Hello!
>
> I've an array:
>
> { "abc" "def" "cba" "fed" "junk" }
>
> I'd like to filter this array by whether the reverse of an element is also
> a member.
>
> In Python, I'd express this as:
>
> >>> array = ["abc", "def", "cba", "fed", "junk"]
> >>> [item for item in array if item[::-1] in array] # [::-1] reverses a
> string
>
> And the result of the list comprehension would be
>
> ['abc', 'def', 'cba', 'fed']
>
> A more functional example would be, e.g:
>
> list(filter(lambda x: x[::-1] in array, array))
>
> For the same result.
>
> How can I do the same thing in Factor? I've tried:
>
> dup [ dup reverse swap member? ] filter
>
> which gives an empty array because the quotation fails for each item.
>
> Regards, cat.
>
>
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