[Agda] strange mismatch

[Andrés Sicard-Ramírez]

On 24 May 2017 at 14:35, Sergei Meshveliani <mechvel at botik.ru> wrote:
> On Wed, 2017-05-24 at 22:13 +0300, Sergei Meshveliani wrote:
>> Please, what is wrong here?
>>
>> test1  is type-checked, and  test2  is not
>> (in Agda 2.6.0-207bde6) :
>
>> -----------------------------------------------------------------------
>> open import Relation.Binary.PropositionalEquality as PE using (_≡_)
>>
>> module _ {α} (A : Set α) (zr a : A)
>>   where
>>   data Expression : Set α where
>>                           con  : A → Expression
>>                           _:+_ : Expression → Expression → Expression
>>
>>   f : Expression → Expression → Expression
>>   f (con zr) y        =  y
>>   f x        (con zr) =  x
>>   f x        y        =  x :+ y
>>
>>   test1 :  f (con zr) (con a) ≡ con a
>>   test1 =  PE.refl
>>
>>   test2 :  f (con a) (con zr) ≡ con a
>>   test2 =  PE.refl
>> ------------------------------------------------------------------------
>>
>> How to fix?
>
>
> May be, listing  "zr a"  in parameters does not imply that  a  does not
> match against zr.
> I am not sure.
>
> May be, I have instead to add to  Expression  the constructors
>     zr : Expression
>     a  : Expression,
>
> and this will imply that  a  does not match against zr.

Note that the `zr` in equations

  f (con zr) y        =  y
  f x        (con zr) =  x

is *different* from the `zr` in the parameters.



--
Andrés
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