[Haskell-beginners] List comprehension question

[Daniel Fischer]

On Wednesday 23 November 2011, 01:08:26, Lee Short wrote:
>  So hlint suggests that I convert the line
> 
>  checked = if ival==input   then [("checked","checked")]  else []
> 
>  to
> 
>  checked = [("checked","checked") | ival==input]
> 
>  I'm not really sure why this works.  Is there some implicit list being
>  filtered by ival==input?  What's going on?

A list comprehension

[expression | condition]

desugars to

if condition then [expression] else []

IMO, that's one of the places where hlint doesn't suggest an improvement.