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

[Brandon Allbery]

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 <harendra.kumar at gmail.com>
wrote:

> 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 <allbery.b at gmail.com> wrote:
>
>> On Thu, Feb 23, 2017 at 9:05 PM, Harendra Kumar <harendra.kumar at gmail.com
>> > wrote:
>>
>>> 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:
>>>
>>> >> let 1 = 2
>>>
>>> >> 1
>>>
>>> 1
>>>
>>> >>
>>>
>>> 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 at gmail.com
>> ballbery at sinenomine.net
>> unix, openafs, kerberos, infrastructure, xmonad
>> http://sinenomine.net
>>
>
>


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