setting local variables via eval

11/03/2008, 05h20

thought some here might appreciate this

http://drawohara.com/post/28514698

kind regards

a @ http://codeforpeople.com/
--
share your knowledge. it's a way to achieve immortality.
h.h. the 14th dalai lama

11/03/2008, 07h23

ara howard wrote:
> http://drawohara.com/post/28514698

Nice hack, as usual

Isn't

class Object
def scope
lambda{ }
end
end

enough? You don't need to return binding from the lambda, AFAICT. The
lambda never gets called.

Also, an alternative to mucking with ObjectSpace:

Thread.current[:val] = v
definition = "#{ var } = Thread.current[:val]"

in place of

value = "ObjectSpace._id2ref #{ v.object_id }"
definition = "#{ var } = #{ value }"

Of course, the value of Thread.current[:val] should be saved and
restored. Maybe this makes the hack jruby friendly.

There is one case in which the double_quoted_heredoc is not hygienic,
when a line of @template begins with __template__:

view2 = View.new '__template__'
view3 = View.new view2.render
puts view3.render

But I don't see any hygienic solution (indenting and using <<- doesn't
work, because the interpolated strings might have line breaks). Maybe
ruby needs a heredoc variant that runs to eof.

With these changes, your code becomes:

class Object
def scope
lambda{ }
end
end

class View
def initialize template
@template = template
end

def render locals = {}
old_val = Thread.current[:val]
context = scope
locals.each do |k, v|
var = k
Thread.current[:val] = v
definition = "#{ var } = Thread.current[:val]"
eval definition, context
end
double_quoted_heredoc = ['<<__template__', @template,
'__template__'].join("\n")
eval double_quoted_heredoc, context
ensure
Thread.current[:val] = old_val
end
end

view = View.new '<body> #{ x + y } </body>'

puts view.render(:x => 40, :y => 2) #=> <body> 42 </body>

--
vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407

11/03/2008, 12h28

On Tue, Mar 11, 2008 at 5:20 AM, ara howard <ara.t.howard@gmail.com> wrote:
>
> thought some here might appreciate this
>
> http://drawohara.com/post/28514698
>
> kind regards
>
> a @ http://codeforpeople.com/
> --
> share your knowledge. it's a way to achieve immortality.
> h.h. the 14th dalai lama
>
>
>
>

Ara

Obviously I miss something, but I have the feeling that this
simplification still works, which use cases did I miss?
The idea is crazy of course

class View
def initialize template
@template = template
end

def render locals = {}
context = binding
locals.each do |k, v|
definition = "#{ k } = #{ v }"
eval definition, context
end
double_quoted_heredoc = ['<<__template__', @template,
'__template__'].join("\n")
eval double_quoted_heredoc, context
end
end

view = View.new '<body> #{ x + y } </body>'
puts view.render(:x => 40, :y => 2) #=> <body> 42 </body>

Cheers
Robert

--
http://ruby-smalltalk.blogspot.com/

---
Whereof one cannot speak, thereof one must be silent.
Ludwig Wittgenstein

11/03/2008, 16h48

On Mar 11, 2008, at 12:23 AM, Joel VanderWerf wrote:

> ara howard wrote:
>> http://drawohara.com/post/28514698
>
> Nice hack, as usual

>
> Isn't
>
> class Object
> def scope
> lambda{ }
> end
> end
>
> enough? You don't need to return binding from the lambda, AFAICT.
> The lambda never gets called.

that's what i head originally - but blows up in 1.9 which requires a
binding

>
>
> Also, an alternative to mucking with ObjectSpace:
>
> Thread.current[:val] = v
> definition = "#{ var } = Thread.current[:val]"
>
> in place of
>
> value = "ObjectSpace._id2ref #{ v.object_id }"
> definition = "#{ var } = #{ value }"
>
> Of course, the value of Thread.current[:val] should be saved and
> restored. Maybe this makes the hack jruby friendly.
>

oh very nice. yeah, pushing and popping from Thread.current is very
good

> There is one case in which the double_quoted_heredoc is not
> hygienic, when a line of @template begins with __template__:
>
> view2 = View.new '__template__'
> view3 = View.new view2.render
> puts view3.render
>
> But I don't see any hygienic solution (indenting and using <<-
> doesn't work, because the interpolated strings might have line
> breaks). Maybe ruby needs a heredoc variant that runs to eof.
>

yes. in real code i generate the hdoc in a loop roughly like so

loop {
hdoc =
"__a
#{ rand(2**30).to_i }__b#{ rand(2**30).to_i }__c#{ rand(2**30).to_i }__"

break unless template =~ Regexp.escape(hdoc)
}

etc

great suggestions - the jruby/Thread.current esp.

thx.

a @ http://drawohara.com/
--
sleep is the best meditation.
h.h. the 14th dalai lama

11/03/2008, 16h52

On Mar 11, 2008, at 5:28 AM, Robert Dober wrote:

> Ara
>
> Obviously I miss something, but I have the feeling that this
> simplification still works, which use cases did I miss?
> The idea is crazy of course

>
> class View
> def initialize template
> @template = template
> end
>
> def render locals = {}
> context = binding
> locals.each do |k, v|
> definition = "#{ k } = #{ v }"
> eval definition, context
> end
> double_quoted_heredoc = ['<<__template__', @template,
> '__template__'].join("\n")
> eval double_quoted_heredoc, context
> end
> end
>
> view = View.new '<body> #{ x + y } </body>'
> puts view.render(:x => 40, :y => 2) #=> <body> 42 </body>
>
> Cheers
> Robert

cfp2:~ > cat a.rb
require 'yaml'

locals = {
'K' => 'or any thing else really',
'k' => %w( list of words ),
}

context = binding

locals.each do |k, v|
begin
definition = "#{ k } = #{ v }"

y 'k' => k, 'v' => v, 'definition' => definition

eval definition, context

rescue Object => e
y 'error' => "#{ e.message } (#{ e.class })"
end
end

cfp2:~ > ruby a.rb
---
v:
- list
- of
- words
k: k
definition: k = listofwords

---
error: undefined local variable or method `listofwords' for
main:Object (NameError)

---
v: or any thing else really
k: K
definition: K = or any thing else really

---
error: |-
compile error
b.rb:8: syntax error, unexpected kOR
K = or any thing else really
^ (SyntaxError)

;-))

a @ http://drawohara.com/
--
sleep is the best meditation.
h.h. the 14th dalai lama

11/03/2008, 17h01

On Mar 11, 2008, at 12:23 AM, Joel VanderWerf wrote:

> enough? You don't need to return binding from the lambda, AFAICT.
> The lambda never gets called.

i just realized that

def scope
binding
end

is what i am acually using - sorry for confusion

a @ http://codeforpeople.com/
--
share your knowledge. it's a way to achieve immortality.
h.h. the 14th dalai lama

11/03/2008, 18h52

ara howard wrote:
> yes. in real code i generate the hdoc in a loop roughly like so
>
> loop {
> hdoc = "__a#{ rand(2**30).to_i }__b#{ rand(2**30).to_i }__c#{
> rand(2**30).to_i }__"
>
> break unless template =~ Regexp.escape(hdoc)
> }

Or:

hdoc = "__template"
while /^#{hdoc}/ =~ @template
hdoc.succ!
p hdoc
end
double_quoted_heredoc = ["<<#{hdoc}", @template, hdoc].join("\n")
eval double_quoted_heredoc, context

--
vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407

12/03/2008, 00h27

Robert Dober wrote:
> Obviously I miss something, but I have the feeling that this
> simplification still works, which use cases did I miss?
> ...
> puts view.render(:x => 40, :y => 2) #=> <body> 42 </body>

Try running it with the following:

puts view.render(:context => 40, :y => 2) #=> TypeError

Ara's "scope" method contains no local variables for yours to step on.

Nice trick Ara - I always appreciate your insights. I had to play with
this one a bit before properly understanding it :-)

Clifford Heath.

11/03/2008, 05h20	#1
ara howard Messages: n/a Hébergeur:	setting local variables via eval thought some here might appreciate this http://drawohara.com/post/28514698 kind regards a @ http://codeforpeople.com/ -- share your knowledge. it's a way to achieve immortality. h.h. the 14th dalai lama

11/03/2008, 07h23	#2
Joel VanderWerf Messages: n/a Hébergeur:	Re: setting local variables via eval ara howard wrote: > http://drawohara.com/post/28514698 Nice hack, as usual Isn't class Object def scope lambda{ } end end enough? You don't need to return binding from the lambda, AFAICT. The lambda never gets called. Also, an alternative to mucking with ObjectSpace: Thread.current[:val] = v definition = "#{ var } = Thread.current[:val]" in place of value = "ObjectSpace._id2ref #{ v.object_id }" definition = "#{ var } = #{ value }" Of course, the value of Thread.current[:val] should be saved and restored. Maybe this makes the hack jruby friendly. There is one case in which the double_quoted_heredoc is not hygienic, when a line of @template begins with __template__: view2 = View.new '__template__' view3 = View.new view2.render puts view3.render But I don't see any hygienic solution (indenting and using <<- doesn't work, because the interpolated strings might have line breaks). Maybe ruby needs a heredoc variant that runs to eof. With these changes, your code becomes: class Object def scope lambda{ } end end class View def initialize template @template = template end def render locals = {} old_val = Thread.current[:val] context = scope locals.each do \|k, v\| var = k Thread.current[:val] = v definition = "#{ var } = Thread.current[:val]" eval definition, context end double_quoted_heredoc = ['<<__template__', @template, '__template__'].join("\n") eval double_quoted_heredoc, context ensure Thread.current[:val] = old_val end end view = View.new '<body> #{ x + y } </body>' puts view.render(:x => 40, :y => 2) #=> <body> 42 </body> -- vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407

11/03/2008, 12h28	#3
Robert Dober Messages: n/a Hébergeur:	Re: setting local variables via eval On Tue, Mar 11, 2008 at 5:20 AM, ara howard <ara.t.howard@gmail.com> wrote: > > thought some here might appreciate this > > http://drawohara.com/post/28514698 > > kind regards > > a @ http://codeforpeople.com/ > -- > share your knowledge. it's a way to achieve immortality. > h.h. the 14th dalai lama > > > > Ara Obviously I miss something, but I have the feeling that this simplification still works, which use cases did I miss? The idea is crazy of course class View def initialize template @template = template end def render locals = {} context = binding locals.each do \|k, v\| definition = "#{ k } = #{ v }" eval definition, context end double_quoted_heredoc = ['<<__template__', @template, '__template__'].join("\n") eval double_quoted_heredoc, context end end view = View.new '<body> #{ x + y } </body>' puts view.render(:x => 40, :y => 2) #=> <body> 42 </body> Cheers Robert -- http://ruby-smalltalk.blogspot.com/ --- Whereof one cannot speak, thereof one must be silent. Ludwig Wittgenstein

11/03/2008, 16h48	#4
ara howard Messages: n/a Hébergeur:	Re: setting local variables via eval On Mar 11, 2008, at 12:23 AM, Joel VanderWerf wrote: > ara howard wrote: >> http://drawohara.com/post/28514698 > > Nice hack, as usual > > Isn't > > class Object > def scope > lambda{ } > end > end > > enough? You don't need to return binding from the lambda, AFAICT. > The lambda never gets called. that's what i head originally - but blows up in 1.9 which requires a binding > > > Also, an alternative to mucking with ObjectSpace: > > Thread.current[:val] = v > definition = "#{ var } = Thread.current[:val]" > > in place of > > value = "ObjectSpace._id2ref #{ v.object_id }" > definition = "#{ var } = #{ value }" > > Of course, the value of Thread.current[:val] should be saved and > restored. Maybe this makes the hack jruby friendly. > oh very nice. yeah, pushing and popping from Thread.current is very good > There is one case in which the double_quoted_heredoc is not > hygienic, when a line of @template begins with __template__: > > view2 = View.new '__template__' > view3 = View.new view2.render > puts view3.render > > But I don't see any hygienic solution (indenting and using <<- > doesn't work, because the interpolated strings might have line > breaks). Maybe ruby needs a heredoc variant that runs to eof. > yes. in real code i generate the hdoc in a loop roughly like so loop { hdoc = "__a #{ rand(230).to_i }__b#{ rand(230).to_i }__c#{ rand(2**30).to_i }__" break unless template =~ Regexp.escape(hdoc) } etc great suggestions - the jruby/Thread.current esp. thx. a @ http://drawohara.com/ -- sleep is the best meditation. h.h. the 14th dalai lama

11/03/2008, 16h52	#5
ara howard Messages: n/a Hébergeur:	Re: setting local variables via eval On Mar 11, 2008, at 5:28 AM, Robert Dober wrote: > Ara > > Obviously I miss something, but I have the feeling that this > simplification still works, which use cases did I miss? > The idea is crazy of course > > class View > def initialize template > @template = template > end > > def render locals = {} > context = binding > locals.each do \|k, v\| > definition = "#{ k } = #{ v }" > eval definition, context > end > double_quoted_heredoc = ['<<__template__', @template, > '__template__'].join("\n") > eval double_quoted_heredoc, context > end > end > > view = View.new '<body> #{ x + y } </body>' > puts view.render(:x => 40, :y => 2) #=> <body> 42 </body> > > Cheers > Robert cfp2:~ > cat a.rb require 'yaml' locals = { 'K' => 'or any thing else really', 'k' => %w( list of words ), } context = binding locals.each do \|k, v\| begin definition = "#{ k } = #{ v }" y 'k' => k, 'v' => v, 'definition' => definition eval definition, context rescue Object => e y 'error' => "#{ e.message } (#{ e.class })" end end cfp2:~ > ruby a.rb --- v: - list - of - words k: k definition: k = listofwords --- error: undefined local variable or method `listofwords' for main:Object (NameError) --- v: or any thing else really k: K definition: K = or any thing else really --- error: \|- compile error b.rb:8: syntax error, unexpected kOR K = or any thing else really ^ (SyntaxError) ;-)) a @ http://drawohara.com/ -- sleep is the best meditation. h.h. the 14th dalai lama

11/03/2008, 17h01	#6
ara howard Messages: n/a Hébergeur:	Re: setting local variables via eval On Mar 11, 2008, at 12:23 AM, Joel VanderWerf wrote: > enough? You don't need to return binding from the lambda, AFAICT. > The lambda never gets called. i just realized that def scope binding end is what i am acually using - sorry for confusion a @ http://codeforpeople.com/ -- share your knowledge. it's a way to achieve immortality. h.h. the 14th dalai lama

11/03/2008, 18h52	#7
Joel VanderWerf Messages: n/a Hébergeur:	Re: setting local variables via eval ara howard wrote: > yes. in real code i generate the hdoc in a loop roughly like so > > loop { > hdoc = "__a#{ rand(230).to_i }__b#{ rand(230).to_i }__c#{ > rand(2**30).to_i }__" > > break unless template =~ Regexp.escape(hdoc) > } Or: hdoc = "__template" while /^#{hdoc}/ =~ @template hdoc.succ! p hdoc end double_quoted_heredoc = ["<<#{hdoc}", @template, hdoc].join("\n") eval double_quoted_heredoc, context -- vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407

12/03/2008, 00h27	#8
Clifford Heath Messages: n/a Hébergeur:	Re: setting local variables via eval Robert Dober wrote: > Obviously I miss something, but I have the feeling that this > simplification still works, which use cases did I miss? > ... > puts view.render(:x => 40, :y => 2) #=> <body> 42 </body> Try running it with the following: puts view.render(:context => 40, :y => 2) #=> TypeError Ara's "scope" method contains no local variables for yours to step on. Nice trick Ara - I always appreciate your insights. I had to play with this one a bit before properly understanding it :-) Clifford Heath.

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