Yegappan Lakshmanan

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Jul 19, 2019, 1:56:02 AM7/19/19

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I have ported the diff sent by Dave Eggum in 2006 to add support
for conditional assignment using ?=.

The following item in the todo list refers to this:

Add ":let var ?= value", conditional assignment. Patch by Dave Eggum,
2006 Dec 11.

The e-mail thread is here:

https://marc.info/?l=vim-dev&m=116591795423455&w=2

You can view, comment on, or merge this pull request online at:

https://github.com/vim/vim/pull/4695

Commit Summary

Add support for conditional assignment

File Changes

Patch Links:

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Christ van Willegen

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Jul 19, 2019, 2:31:04 AM7/19/19

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Hi,

Op vr 19 jul. 2019 07:56 schreef Yegappan Lakshmanan <vim-dev...@256bit.org>:

I have ported the diff sent by Dave Eggum in 2006 to add support
for conditional assignment using ?=.

The following item in the todo list refers to this:

Add ":let var ?= value", conditional assignment. Patch by Dave Eggum,
2006 Dec 11.

There are one or two places in the patch that include code or comments that implements the .= operator.

Is that intentional?

Christ van Willegen

vim-dev ML

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Jul 19, 2019, 2:31:33 AM7/19/19

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Hi,

Op vr 19 jul. 2019 07:56 schreef Yegappan Lakshmanan <
vim-dev...@256bit.org>:

> I have ported the diff sent by Dave Eggum in 2006 to add support
> for conditional assignment using ?=.
>
> The following item in the todo list refers to this:
>

> - Add ":let var ?= value", conditional assignment. Patch by Dave Eggum,
> 2006 Dec 11.
>

> There are one or two places in the patch that include code or comments
that implements the .= operator.

Is that intentional?

Christ van Willegen

>

Yegappan Lakshmanan

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Jul 19, 2019, 2:39:25 AM7/19/19

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Hi,

Which part of the diff are you referring to? All the changes in the diff
are related to "?=".

Regards,
Yegappan

vim-dev ML

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Jul 19, 2019, 2:40:05 AM7/19/19

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Hi,

On Thu, Jul 18, 2019 at 11:31 PM Christ van Willegen
<cvwil...@gmail.com> wrote:
>
> Hi,
>
> Op vr 19 jul. 2019 07:56 schreef Yegappan Lakshmanan <vim-dev...@256bit.org>:
>>

>> I have ported the diff sent by Dave Eggum in 2006 to add support
>> for conditional assignment using ?=.
>>
>> The following item in the todo list refers to this:
>>
>> Add ":let var ?= value", conditional assignment. Patch by Dave Eggum,
>> 2006 Dec 11.
>

> There are one or two places in the patch that include code or comments that implements the .= operator.
>

Which part of the diff are you referring to? All the changes in the diff
are related to "?=".

Regards,
Yegappan

> Is that intentional?
>
> Christ van Willegen
>

K.Takata

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Jul 19, 2019, 2:43:51 AM7/19/19

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@k-takata commented on this pull request.

In src/eval.c:

> @@ -1487,8 +1488,8 @@ ex_let_const(exarg_T *eap, int is_const)
  * Assign the typevalue "tv" to the variable or variables at "arg_start".
  * Handles both "var" with any type and "[var, var; var]" with a list type.
  * When "nextchars" is not NULL it points to a string with characters that
- * must appear after the variable(s).  Use "+", "-" or "." for add, subtract
- * or concatenate.
+ * must appear after the variable(s).  Use "+", "-", "." or "?" for add,
+ * subtract concatenate or conditionally assign.

s/subtract/subtract,/

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Codecov

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Jul 19, 2019, 3:11:14 AM7/19/19

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Codecov Report

Merging #4695 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@

##           master    #4695      +/-   ##

==========================================

+ Coverage   81.35%   81.35%   +<.01%     

==========================================

  Files         114      114              

  Lines      145212   145219       +7     

==========================================

+ Hits       118130   118136       +6     

- Misses      27082    27083       +1

Impacted Files	Coverage Δ
src/eval.c	`86.34% <100%> (+0.02%)`	⬆️
src/profiler.c	`92.69% <0%> (-0.57%)`	⬇️
src/gui_gtk_x11.c	`57.86% <0%> (-0.1%)`	⬇️
src/window.c	`87.33% <0%> (-0.04%)`	⬇️
src/term.c	`79.16% <0%> (+0.05%)`	⬆️
src/if_xcmdsrv.c	`86.17% <0%> (+0.53%)`	⬆️

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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FUJIWARA Takuya

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Jul 19, 2019, 4:20:55 AM7/19/19

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I usually use get() for this purpose.

let default_value = 42
let g:myplugin_globalvar = get(g:, 'myplugin_globalvar', default_value)

I think get() is enough, but if someone wants this patch,
I want also binary operator for consistency.

let a ?= b
let a = a ? b

It doesn't work (because ? is already used for ternary operator a ? b : c).
so I would like to propose ??=.

let a ??= b
let a = a ?? b

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mattn

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Jul 19, 2019, 4:25:03 AM7/19/19

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Do not merge this.

if !exists("foo")
  let foo = "bar"
endif

This documentation is NOT right. This implementation is:

let tmp = "bar"
if !exists("foo")
  let foo = tmp
endif
unlet tmp

For example, if the RHS (right-hand-side) is calling function, the function is always evaluated even if the operator is "?=".

let foo ?= s:bar()

Because this syntax is below.

let tmp = s:bar()
if !exists("foo")
  let foo = tmp
endif
unlet tmp

i.e. Current implementation does not skip right-hand-side. The 4th argument of set_var_lval is passed as already evaluated value when the set_var_lval will be called. If you want to implement this as your expected, the RHS must not be evaluated.

function s:update()
  let s:foo = 2
  return s:foo
endfunction

"let s:foo = 1
let s:foo ?= s:update()

You need to change all of the part calling set_var_lval.

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Bram Moolenaar

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Jul 19, 2019, 6:18:21 AM7/19/19

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> I usually use `get()` for this purpose.

I also wonder if adding ?= is useful enough. Most languages don't
support this. Wikipedia only mentions its use in regexp.

> ```vim

> let default_value = 42
> let g:myplugin_globalvar = get(g:, 'myplugin_globalvar', default_value)

> ```
>
> ---

>
> I think `get()` is enough, but if someone wants this patch,
> I want also binary operator for consistency.
>

> ```vim

> let a ?= b
> let a = a ? b
> ```
>

> It doesn't work (because `?` is already used for ternary operator `a ? b : c`).
> so I would like to propose `??=`.
>
> ```vim

> let a ??= b
> let a = a ?? b

> ```

Isn't that ?:, the Elvis operator?

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[real standing law in Pennsylvania, United States of America]

/// Bram Moolenaar -- Br...@Moolenaar.net -- http://www.Moolenaar.net \\\
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FUJIWARA Takuya

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Jul 19, 2019, 6:44:53 AM7/19/19

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@brammool

Isn't that ?:, the Elvis operator?

Ah sorry, firstly I see this PR,
I thought let a ?= b is same as let a = a ? a : b (like elvis operator).
My ?? proposal is based on the misunderstanding 😓

In my conclusion, I think ?= is not necessary after all.

Christ van Willegen

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Jul 20, 2019, 9:28:40 AM7/20/19

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Hi Yegappan,

On Fri, Jul 19, 2019 at 8:39 AM Yegappan Lakshmanan <yega...@gmail.com> wrote:
> On Thu, Jul 18, 2019 at 11:31 PM Christ van Willegen
> <cvwil...@gmail.com> wrote:
> >
> > Hi,
> >
> > Op vr 19 jul. 2019 07:56 schreef Yegappan Lakshmanan <vim-dev...@256bit.org>:
> >>
> >> I have ported the diff sent by Dave Eggum in 2006 to add support
> >> for conditional assignment using ?=.
> >>
> >> The following item in the todo list refers to this:
> >>
> >> Add ":let var ?= value", conditional assignment. Patch by Dave Eggum,
> >> 2006 Dec 11.
> >
> > There are one or two places in the patch that include code or comments that implements the .= operator.
> >
>
> Which part of the diff are you referring to? All the changes in the diff
> are related to "?=".

I was thrown off by these lines:

- if (*expr != '=' && !((vim_strchr((char_u *)"+-*/%", *expr) != NULL
+ if (*expr != '=' && !((vim_strchr((char_u *)"+-*/%?", *expr) != NULL
&& expr[1] == '=') || concat))

(That I now see totally misread! I just went "Oooh" when I revisited the patch).

I _thought_ that the original code did not use the '|| concat' in the
second line. I totally missed that there was no + in fron of it, so I
thought it was a change with respect to the original code.

Also, I misread this:

- * must appear after the variable(s). Use "+", "-" or "." for add, subtract
- * or concatenate.
+ * must appear after the variable(s). Use "+", "-", "." or "?" for add,

+ * subtract, concatenate or conditionally assign.

Because the "." was originally after the 'or', I didn't see that it
was in the original code as well...

This should teach me to:

- Read the patch carefully
- Re-read the patch carefully
- Think
- Think harder
- Only _then_ complain on the mailing list about wrong code...

Christ van Willegen

vim-dev ML

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Jul 20, 2019, 9:29:01 AM7/20/19

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Hi Yegappan,

On Fri, Jul 19, 2019 at 8:39 AM Yegappan Lakshmanan <yega...@gmail.com> wrote:
> On Thu, Jul 18, 2019 at 11:31 PM Christ van Willegen
> <cvwil...@gmail.com> wrote:
> >
> > Hi,
> >
> > Op vr 19 jul. 2019 07:56 schreef Yegappan Lakshmanan <vim-dev...@256bit.org>:
> >>

> >> I have ported the diff sent by Dave Eggum in 2006 to add support
> >> for conditional assignment using ?=.
> >>
> >> The following item in the todo list refers to this:
> >>
> >> Add ":let var ?= value", conditional assignment. Patch by Dave Eggum,
> >> 2006 Dec 11.
> >

Bram Moolenaar

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Jul 21, 2019, 8:49:00 AM7/21/19

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I find this operator rather obscure, I can't find it in popular languages.
Also, it's easy enough to use the "if" construct. It's more lines, but it's easier to understand.
I also haven't heard anyone ask for this, and suspect it won't be used much because plugin developers do not know it exists.
Keeping the Vim script language simple is more important, in my opinion.

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Bram Moolenaar

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Jul 21, 2019, 8:49:03 AM7/21/19

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Closed #4695.

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Yegappan Lakshmanan

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Jul 21, 2019, 11:44:24 AM7/21/19

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Hi Bram,

On Sun, Jul 21, 2019 at 5:49 AM Bram Moolenaar
<vim-dev...@256bit.org> wrote:
>
> I find this operator rather obscure, I can't find it in popular languages.
> Also, it's easy enough to use the "if" construct. It's more lines, but it's easier to understand.
> I also haven't heard anyone ask for this, and suspect it won't be used much because plugin developers do not know it exists.
> Keeping the Vim script language simple is more important, in my opinion.
>

In that case, the following item needs to be removed from the todo list:

- Add ":let var ?= value", conditional assignment. Patch by Dave Eggum,
2006 Dec 11.

I found that only Ruby has an operator (||=) for the default assignment.
Other languages are referring to using the ternary operator for this.
In these cases, the operator is used only in the RHS expression.

- Yegappan

vim-dev ML

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Jul 21, 2019, 11:44:48 AM7/21/19

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Hi Bram,

On Sun, Jul 21, 2019 at 5:49 AM Bram Moolenaar
<vim-dev...@256bit.org> wrote:
>
> I find this operator rather obscure, I can't find it in popular languages.
> Also, it's easy enough to use the "if" construct. It's more lines, but it's easier to understand.
> I also haven't heard anyone ask for this, and suspect it won't be used much because plugin developers do not know it exists.
> Keeping the Vim script language simple is more important, in my opinion.
>

In that case, the following item needs to be removed from the todo list:

- Add ":let var ?= value", conditional assignment. Patch by Dave Eggum,
2006 Dec 11.

I found that only Ruby has an operator (||=) for the default assignment.
Other languages are referring to using the ternary operator for this.
In these cases, the operator is used only in the RHS expression.

- Yegappan

Yegappan Lakshmanan

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Jul 21, 2019, 11:49:44 AM7/21/19

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Hi,

On Fri, Jul 19, 2019 at 1:20 AM FUJIWARA Takuya
<vim-dev...@256bit.org> wrote:
>
> I usually use get() for this purpose.
>
> let default_value = 42
> let g:myplugin_globalvar = get(g:, 'myplugin_globalvar', default_value)
>

This example of using the get() function with the g: dictionary to get
either the current value or the default value of a variable should be
mentioned somewhere in the help.

Regards,
Yegappan

vim-dev ML

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Jul 21, 2019, 11:50:10 AM7/21/19

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Bram Moolenaar

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Jul 21, 2019, 12:10:00 PM7/21/19

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Yegappan wrote:

> On Sun, Jul 21, 2019 at 5:49 AM Bram Moolenaar
> <vim-dev...@256bit.org> wrote:
> >
> > I find this operator rather obscure, I can't find it in popular languages.
> > Also, it's easy enough to use the "if" construct. It's more lines, but it's easier to understand.
> > I also haven't heard anyone ask for this, and suspect it won't be used much because plugin developers do not know it exists.
> > Keeping the Vim script language simple is more important, in my opinion.
> >
>
> In that case, the following item needs to be removed from the todo list:
>
> - Add ":let var ?= value", conditional assignment. Patch by Dave Eggum,
> 2006 Dec 11.

I'll remove that.

> I found that only Ruby has an operator (||=) for the default assignment.
> Other languages are referring to using the ternary operator for this.
> In these cases, the operator is used only in the RHS expression.

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Christ out, if possible; Loose "I fart in your general direction"; Lose
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vim-dev ML

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Jul 21, 2019, 12:10:24 PM7/21/19

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Yegappan wrote:

> On Sun, Jul 21, 2019 at 5:49 AM Bram Moolenaar
> <vim-dev...@256bit.org> wrote:
> >
> > I find this operator rather obscure, I can't find it in popular languages.
> > Also, it's easy enough to use the "if" construct. It's more lines, but it's easier to understand.
> > I also haven't heard anyone ask for this, and suspect it won't be used much because plugin developers do not know it exists.
> > Keeping the Vim script language simple is more important, in my opinion.
> >
>
> In that case, the following item needs to be removed from the todo list:
>

> - Add ":let var ?= value", conditional assignment. Patch by Dave Eggum,
> 2006 Dec 11.

I'll remove that.

> I found that only Ruby has an operator (||=) for the default assignment.
> Other languages are referring to using the ternary operator for this.
> In these cases, the operator is used only in the RHS expression.

--
(letter from Mark to Mike, about the film's probable certificate)
For an 'A' we would have to: Lose as many shits as possible; Take Jesus
Christ out, if possible; Loose "I fart in your general direction"; Lose
"the oral sex"; Lose "oh, fuck off"; Lose "We make castanets out of your
testicles"
"Monty Python and the Holy Grail" PYTHON (MONTY) PICTURES LTD

/// Bram Moolenaar -- Br...@Moolenaar.net -- http://www.Moolenaar.net \\\
/// sponsor Vim, vote for features -- http://www.Vim.org/sponsor/ \\\
\\\ an exciting new programming language -- http://www.Zimbu.org ///
\\\ help me help AIDS victims -- http://ICCF-Holland.org ///

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[vim/vim] Add support for conditional assignment using ?= (#4695)

Yegappan Lakshmanan

You can view, comment on, or merge this pull request online at:

Commit Summary

File Changes

Patch Links:

Christ van Willegen

vim-dev ML

Yegappan Lakshmanan

vim-dev ML

K.Takata

Codecov

Codecov Report

FUJIWARA Takuya

mattn

Bram Moolenaar

FUJIWARA Takuya

Christ van Willegen

vim-dev ML

Bram Moolenaar

Bram Moolenaar

Yegappan Lakshmanan

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Yegappan Lakshmanan

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Bram Moolenaar

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