# Lambda and a Proc

**URL:** <https://www.ruby-forum.com/t/lambda-and-a-proc/170464>\
**Category:** Ruby\
**Created:** [June 17, 2009, 8:15pm UTC](https://www.ruby-forum.com/t/lambda-and-a-proc/170464 "2009-06-17T20:15:42Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![aidy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/eada6e/32.png) [@aidy](https://www.ruby-forum.com/u/aidy)\
**Post date:** [June 17, 2009, 8:15pm UTC](https://www.ruby-forum.com/t/lambda-and-a-proc/170464/1 "2009-06-17T20:15:42Z")

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Hi,

I am a bit unsure on what the difference is between a lambda and a  
Proc?

hello = lambda { puts(‘aidy, aidy, aidy’ ) }  
hello.call

hello = Proc.new{ puts(‘aidy, aidy, aidy’ ) }  
hello.call

Cheers

Aidy

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<div class="post-metadata">

**Author:** ![aidy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/eada6e/32.png) [@aidy](https://www.ruby-forum.com/u/aidy)\
**Post date:** [June 17, 2009, 9:18pm UTC](https://www.ruby-forum.com/t/lambda-and-a-proc/170464/2 "2009-06-17T21:18:30Z")

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On Wed, Jun 17, 2009 at 7:15 PM, aidy [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> Cheers
> 
> Aidy

There is a great description of the differences on wikipedia:

[http://en.wikibooks.org/wiki/Ruby\_Programming/Syntax/Method\_Calls#Understanding\_blocks.2C\_Procs\_and\_methods](http://en.wikibooks.org/wiki/Ruby_Programming/Syntax/Method_Calls#Understanding_blocks.2C_Procs_and_methods)

Give that a read.

Ben

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<div class="post-metadata">

**Author:** ![aidy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/eada6e/32.png) [@aidy](https://www.ruby-forum.com/u/aidy)\
**Post date:** [June 17, 2009, 9:34pm UTC](https://www.ruby-forum.com/t/lambda-and-a-proc/170464/3 "2009-06-17T21:34:22Z")

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On Wed, Jun 17, 2009 at 2:15 PM, aidy[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> Hi,
> 
> I am a bit unsure on what the difference is between a lambda and a  
> Proc?
> 
> hello = lambda { puts(‘aidy, aidy, aidy’ ) }  
> hello.call
> 
> hello = Proc.new{ puts(‘aidy, aidy, aidy’ ) }  
> hello.call

Well no differences that affect the above code, but

a return in a lambda block causes the block to evaluate to the value  
of the return, in a proc block it causes a return from the method  
where the block was created.  
rb(main):011:0\> def foo\_lambda  
irb(main):012:1\> lambda {return 42}  
irb(main):013:1\> end  
=\> nil  
irb(main):015:0\> foo\_lambda.call  
=\> 42

irb(main):028:0\> def bar\_lambda  
irb(main):029:1\> p = lambda {return 42}  
irb(main):030:1\> puts “calling p #{p.call}”  
irb(main):031:1\> puts “back from call”  
irb(main):032:1\> p  
irb(main):033:1\> end  
=\> nil  
irb(main):034:0\> bar\_lambda.call  
calling p 42  
back from call  
=\> 42

irb(main):005:0\> def bar  
irb(main):006:1\> p = Proc.new {return 42}  
irb(main):007:1\> p.call  
irb(main):008:1\> puts “after call”  
irb(main):009:1\> end  
=\> nil  
irb(main):010:0\> bar  
=\> 42

rb(main):001:0\> def foo  
irb(main):002:1\> Proc.new {return 42}  
irb(main):003:1\> end  
=\> nil  
irb(main):004:0\> foo.call  
LocalJumpError: unexpected return  
from (irb):2:in `foo' from (irb):4:in `call’  
from (irb):4

And in Ruby 1.9 lambdas raise an ArgumentError when called with the  
wrong number of arguments, a Proc will set missing arguments to nil,  
and ignore extra arguments.

The way I think of this is that lambdas act more like nameless methods.

–  
Rick DeNatale

Blog: [http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/)  
Twitter: [http://twitter.com/RickDeNatale](http://twitter.com/RickDeNatale)  
WWR: [http://www.workingwithrails.com/person/9021-rick-denatale](http://www.workingwithrails.com/person/9021-rick-denatale)  
LinkedIn: [http://www.linkedin.com/in/rickdenatale](http://www.linkedin.com/in/rickdenatale)