### `++murn`

Maybe transform

Passes each member of `++list` `a` to gate `b`, which must produce a
`++unit`.  Produces a new list with all the results that do not produce
`~`.

Accepts
-------

`a` is a list.

`b` is a gate that produces a unit.

Produces
--------

A unit.

Source
------

    ++  murn                                                ::  maybe transform
      ~/  %murn
      |*  {a/(list) b/$-(* (unit))}
      |-
      ?~  a  ~
      =+  c=(b i.a)
      ?~  c
        $(a t.a)
      [i=u.c t=$(a t.a)]

Examples
--------

    ~zod/try=> =a |=(a=@ ?.((gte a 2) ~ (some (add a 10))))
    ~zod/try=> (murn (limo [0 1 2 3 ~]) a)
    [i=12 t=[i=13 t=~]]



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