Re: [Haskell-cafe] What does "1 = 2" mean in Haskell?

Without a binding it is useless at top level, but if you strictify the pattern it can be useful in `let` (possibly as a sanity check where you want the program to abort if it fails). I don't recall offhand if it desugars usefully in list comprehensions, but if so it would work as a filter. There may also be other specialized use cases; general syntax tends to get reused a lot in Haskell, so making this case a syntax error could make it difficult to support actually useful cases. :) (Also I'm sure someone overly clever could figure out some way to abuse it. :) On Thu, Feb 23, 2017 at 10:41 PM, Harendra Kumar wrote:

On 24 February 2017 at 08:45, Brandon Allbery wrote:

...

Literally the only use I've seen for this was a CCC puzzle. However, it is the trivial case of something that is more useful: pattern matching the result of an expression (say, a Data.Map.lookup when you know the key exists).

Can you explain how that will be useful (without a binding)? Will the pattern match be ever actually tried when there is no binding?

-harendra

-- brandon s allbery kf8nh sine nomine associates allbery.b@gmail.com ballbery@sinenomine.net unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net