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

Are pattern matches which produce no bindings useful in any case? Will it be possible or a good idea for the compiler to produce warnings in such cases? This seems to be just a no-op. -harendra On 24 February 2017 at 08:30, Brandon Allbery wrote:

It is, yes. (Literal numbers in patterns occasionally have unexpected type ramifications as a result; and occasionally others, since the compiler rewrites the pattern match into a guard. It's one of those things that Just Works 99% of the time and then makes you tear your hair out.)

On Thu, Feb 23, 2017 at 9:56 PM, Harendra Kumar wrote:

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My first guess was a pattern match, but it sounded a bit odd because there is no explicit constructor in case of numbers. If there were an explicit constructor it would have been easier to imagine this as a pattern match. This seems to be a weird side effect of the special handling of numbers.

-harendra

On 24 February 2017 at 07:37, Brandon Allbery wrote:

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On Thu, Feb 23, 2017 at 9:05 PM, Harendra Kumar < harendra.kumar@gmail.com> wrote:

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Kids have this amazing ability to break any toy in minutes. I gave my seven year old daughter ghci to play with and in a little while she said it is broken:

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let 1 = 2

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1

1

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Earlier, I had explained to her about symbols and assigning values to symbols, and I said numbers are not symbols. But when she came up with this I could not explain what's going on. How can "1 = 2" be a valid equation? Am I missing something fundamental here, or it is just broken?

It's a pattern match. The match fails, but as it produced no bindings it cannot be observed and its success or failure is irrelevant.

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

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