Ken Takata wrote:
> 2016/9/22 Thu 2:37:29 UTC+9 Bram Moolenaar wrote:
> > Christian Brabandt wrote:
> >
> > > Am 2016-09-21 00:00, schrieb Ken Takata:
> > > > Hi Christian,
> > > >
> > > > 2016/9/21 Wed 5:31:26 UTC+9 Christian Brabandt wrote:
> > > >> Hi,
> > > >> I think I found a bug with lambda expressions.
> > > >>
> > > >> I was looking into writing some automated tests and was trying to use
> > > >> the new lambda expressions. However this does not work as expected:
> > > >>
> > > >> Here is an example:
> > > >> #v+
> > > >> let a = ['FOOBAR "word"', 'FOOBAR "word2"']
> > > >> let pat='^FOOBAR\s\+\zs"[^"]\+"'
> > > >> let pat2='^FOOBAR\s\+\("[^"]\+"\)'
> > > >> :echo map(copy(a), 'matchstr(v:val, g:pat)')
> > > >> -> result ['"word"', '"word2"']
> > > >> :echo map(copy(a), {val -> matchstr(val, g:pat)})
> > > >> -> BUG: result ['""', '""'], expected ['"word"', '"word2"']
> > > >> :echo map(copy(a), 'substitute(v:val, g:pat2,
> > > >> ''\=submatch(1)'',"")')
> > > >> -> result ['"word"', '"word2"']
> > > >> :echo map(copy(a), {val -> substitute(val, g:pat2, '\=submatch(1)',
> > > >> '')})
> > > >> -> BUG: result ['0', '1'], expected ['"word", '"word2"']
> > > >> #v-
> > > >
> > > > This is not a bug. map() always passes two arguments (key and val) to
> > > > the
> > > > specified Funcref. So,
> > > >
> > > >> :echo map(copy(a), {val -> matchstr(val, g:pat)})
> > > >
> > > > this should be:
> > > >
> > > > :echo map(copy(a), {key, val -> matchstr(val, g:pat)})
> > > >
> > > > Or you can still use v:val:
> > > >
> > > > :echo map(copy(a), {-> matchstr(v:val, g:pat)})
> > >
> > > Hm, should there be an error when only one argument is given?
> > > Or at least it should be more stressed in the documentatio, that two
> > > arguments are expected.
> >
> > How about extending the example in the help:
> >
> > If {expr2} is a |Funcref| it is called with two arguments:
> > 1. The key or the index of the current item.
> > 2. the value of the current item.
> > The function must return the new value of the item. Example
> > that changes each value by "key-value": >
> > func KeyValue(key, val)
> > return a:key . '-' . a:val
> > endfunc
> > call map(myDict, function('KeyValue'))
> > < It is shorter when using a |lambda|: >
> > call map(myDict, {key, val -> key . '-' . val})
> > < If you do not use "val" you can leave it out: >
> > call map(myDict, {key -> 'item: ' . key})
>
> A similar update might be needed for `:help filter()`.
How about this:
If {expr2} is a |Funcref| it must take two arguments:
1. the key or the index of the current item.
2. the value of the current item.
The function must return |TRUE| if the item should be kept.
Example that keeps the odd items of a list: >
func Odd(idx, val)
return a:idx % 2 == 1
endfunc
call filter(mylist, function('Odd'))
< It is shorter when using a |lambda|: >
call filter(myList, {idx, val -> idx * val <= 42})
< If you do not use "val" you can leave it out: >
call filter(myList, {idx -> idx % 2 == 1})
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