code review 6482056: text/template: allow grouping of pipelines using parentheses

text/template: allow grouping of pipelines using parentheses

Based on work by Russ Cox. From his CL:

        This is generally useful but especially helpful when trying
        to use the built-in boolean operators.  It lets you write:

        {{if not (f 1)}} foo {{end}}
        {{if and (f 1) (g 2)}} bar {{end}}
        {{if or (f 1) (g 2)}} quux {{end}}

        instead of

        {{if f 1 | not}} foo {{end}}
        {{if f 1}}{{if g 2}} bar {{end}}{{end}}
        {{$do := 0}}{{if f 1}}{{$do := 1}}{{else if g 2}}{{$do := 1}}{{end}}{{if $do}} quux {{end}}

The result can be a bit LISPy but the benefit in expressiveness and readability
for such a small change justifies it.

I believe no changes are required to html/template.

Fixes issue 3276.

[r, 2012-08-23 19:42:16]

Hello golang-dev@googlegroups.com,

I'd like you to review this change to
https://code.google.com/p/go/

[r, 2012-08-23 19:43:09]

	Fixes issue 3276.

[adg, 2012-08-24 03:11:30]

LGTM

[rog, 2012-08-24 07:45:18]

On 2012/08/23 19:42:16, r wrote:
> Hello mailto:golang-dev@googlegroups.com,
> 
> I'd like you to review this change to
> https://code.google.com/p/go/

It had to happen some time. It'll be interesting to see how far people take
this.

LGTM.

[minux1, 2012-08-24 09:33:04]

On Fri, Aug 24, 2012 at 3:42 AM, <r@golang.org> wrote:

> Description:
> text/template: allow grouping of pipelines using parentheses
>
> Based on work by Russ Cox. From his CL:
>
>         This is generally useful but especially helpful when trying
>         to use the built-in boolean operators.  It lets you write:
>
>         {{if not (f 1)}} foo {{end}}
>         {{if and (f 1) (g 2)}} bar {{end}}
>         {{if or (f 1) (g 2)}} quux {{end}}
>
>         instead of
>
>         {{if f 1 | not}} foo {{end}}
>         {{if f 1}}{{if g 2}} bar {{end}}{{end}}
>         {{$do := 0}}{{if f 1}}{{$do := 1}}{{else if g 2}}{{$do :=
> 1}}{{end}}{{if $do}}quux {{end}}
>
> The result can be a bit LISPy but the benefit in expressiveness and
> readability
> for such a small change justifies it.
>
the proposal SGTM. i've missed this feature for some time,
and i think a LISPy grammar for a template language is just a perfect fit.
(i like lisp so this view might be biased.)

[r, 2012-08-24 19:37:39]

*** Submitted as http://code.google.com/p/go/source/detail?r=a58536973959 ***

text/template: allow grouping of pipelines using parentheses

Based on work by Russ Cox. From his CL:

        This is generally useful but especially helpful when trying
        to use the built-in boolean operators.  It lets you write:

        {{if not (f 1)}} foo {{end}}
        {{if and (f 1) (g 2)}} bar {{end}}
        {{if or (f 1) (g 2)}} quux {{end}}

        instead of

        {{if f 1 | not}} foo {{end}}
        {{if f 1}}{{if g 2}} bar {{end}}{{end}}
        {{$do := 0}}{{if f 1}}{{$do := 1}}{{else if g 2}}{{$do := 1}}{{end}}{{if
$do}} quux {{end}}

The result can be a bit LISPy but the benefit in expressiveness and readability
for such a small change justifies it.

I believe no changes are required to html/template.

Fixes issue 3276.

R=golang-dev, adg, rogpeppe, minux.ma
CC=golang-dev
http://codereview.appspot.com/6482056