meaning of: line, =

[Rustom Mody]

On Friday, February 6, 2015 at 6:40:23 PM UTC+5:30, Devin Jeanpierre wrote:
> Sorry for late reply, I somehow missed this email.
> 
> On Thu, Feb 5, 2015 at 8:59 AM, Rustom Mody wrote:
> > The reason I ask: I sorely miss haskell's pattern matching in python.
> >
> > It goes some way:
> >
> >>>> ((x,y),z) = ((1,2),3)
> >>>> x,y,z
> > (1, 2, 3)
> >
> > But not as far as I would like:
> >
> >>>> ((x,y),3) = ((1,2),3)
> >   File "<stdin>", line 1
> > SyntaxError: can't assign to literal
> >>>>
> >
> > [Haskell]
> >
> > Prelude> let (x, (y, (42, z, "Hello"))) = (1, (2, (42, 3, "Hello")))
> > Prelude> (x,y,z)
> > (1,2,3)
> 
> Yeah, but Haskell is ludicrous.
> 
> Prelude> let (x, 2) = (1, 3)
> Prelude>
> 
> Only non-falsifiable patterns really make sense as the left hand side
> of an assignment in a language without exceptions, IMO. Otherwise you
> should use a match/case statement. (Of course, Python does have
> exceptions...)

Also its good to see the full context of your example:

Prelude> let (x, 2) = (1, 3)
Prelude> x
*** Exception: <interactive>:2:5-19: Irrefutable pattern failed for pattern (x, 2)

Prelude> 


So I am not sure what you find ludicrous.
Haskell is a lazy language. 
This is lazy behavior. What else can it be?

[Does not make me a great fan of laziness -- which is another matter]