refl | Provides a Refl encoding in Rust
kandi X-RAY | refl Summary
kandi X-RAY | refl Summary
Provides a refl encoding which you can use to provide a proof witness that one type is equivalent (identical) to another type. You can use this to encode a subset of what GADTs allow you to in Haskell.
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Community Discussions
Trending Discussions on refl
QUESTION
The PLFA exercise: what if we write the arithmetic more "naturally" in Quantifiers chapter (https://plfa.github.io/Quantifiers/) ?
...ANSWER
Answered 2021-Apr-24 at 06:48∃-even′ ⟨ zero , refl ⟩ = even-zero
∃-even′ ⟨ suc m , refl ⟩ rewrite +-identityʳ m
| +-suc m m
= even-suc (∃-odd′ ⟨ m , help1 m ⟩)
∃-odd′ ⟨ m , refl ⟩ rewrite +-suc (2 * m) 0
| +-identityʳ m
| +-identityʳ (m + m)
| dbl≡2* m
= odd-suc (∃-even′ ⟨ m , refl ⟩)
QUESTION
I have trouble understanding this syntax. I didn't find the answer to my quesion in the Agda tutorial manual. The only thing I found was that (x : A) -> (y : A) -> B
sugars to (x : A)(y : A) -> B
which sugars into (x y : A) -> B
, but this isn't the whole story.
What troubles me is that type declaration:
map : {A B : Set} -> (A -> B) -> List A -> List B
is fine, while
map : {A B : Set} (A -> B) -> List A -> List B
is not.
Version with arrow between arguments
singleton : {A : Set} -> (x : A) → List A
is fine, while the same expression without arrow
singleton : {A : Set}(x : A) → List A
is still fine.
The version with ':' between arguments
...ANSWER
Answered 2021-Apr-20 at 19:00while
QUESTION
I'm working in Cubical agda and trying to build up some common utilities for later proofs. One of these is that for any type A
it is the 'same' as the type Σ A (\_ -> Top)
where Top
is the type with one element. And the issue is how to best expose this 'sameness' from the utility library. I can expose it as an equivalence, a path or an isomorphism, and maybe multiple ones.
I originally exposed it as just a path: top-path : Path A (Σ A (\_ -> Top))
which is built up using glue types from an underlying top-equiv : A ≃ Σ A (\_ -> Top)
. But when trying to use this in later proofs I found out that transporting along this path did not compute as I expected. My expectation was that it composed with fst
to the identity, but in practice I found that it sometimes left in transp
and prim^unglue
terms. This was not the case if I used a particular concrete type for A, or if I used a similar construction using the equivalence.
Example:
...ANSWER
Answered 2021-Apr-08 at 06:41In the agda/cubical
library we do tend to export the equivalence (or the iso) along with the path, because of issues like the one you mention.
The reason for those extra transp
calls is that transport for Glue
has to work in the general case where they might actually be required.
fst (prim^unglue a)
should reduce away if you ask for the normal form though.
QUESTION
Now I know, it's possible to express quantifiers via dependent types. So I wrote a simple realization for this "for all (a, b: N): exists (c: N): c = a + b":
...ANSWER
Answered 2021-Mar-17 at 17:40For Nat
comparison you can use Data.Nat
's GT
(greater than), GTE
(greater-equal than), LT
(less than), LTE
(less-equal than). So GT c a
and LT c b
for c > a
and c < b
.
For and
you can just put both proofs into a tuple: (GT c a, LT c b)
. If, for example, you would have wanted to or
them, you could use Either (GT c a) (LT c b)
.
Thus:
QUESTION
I am creating android application using Aide (mobile ide). My project has no errors but when I run the app, during building APK it displays an error dialog with message :
'Packaging error: com.blankj.utilcode.util.ReflectUtil sSReflectException: java.lang.refle ct.InvocationTargetException '.
This has happened when I added these two libraries in my project:
Dexter library : to handle runtime permission in android
KingsMentor library : to scan barcode or QR code
Please help me how do I fix it?
...ANSWER
Answered 2021-Jan-22 at 12:15Now I know where the actual bug is.
If the same happens to you then kindly note that it is due to the 3rd party library that you are using in your project.
So the solution is to remove that library from your project and try another one , moreover try to code from scratch for that task if possible instead of using such libraries.
It happens because those libraries use another library or libraries.
Hope it helps you.
Happy coding :)
QUESTION
I am trying to make a function which searches for a type in a parameter pack, then creates a lambda which invokes another function with that type as a template parameter e.g.:
...ANSWER
Answered 2021-Jan-19 at 07:21Function parameters are variables. Not variable templates; just regular old variables. And a non-template variable cannot be given template parameters.
You cannot pass a function template anywhere. You can only pass a particular instantiation of a function template. The closest you can get to what you want is to pass a type that has a templated operator()
overload, but unless you can provide the template parameters through deduction, the only way to invoke it is via fn.operator()(params)
. So you may as well have given it a meaningful name.
QUESTION
I want to convert my java map into a Scala immutable map, I have a sample code that works correctly with Scala 2.12 but fails with Scala 2.13.
Setup
untitled14\build.sbt
ANSWER
Answered 2021-Jan-15 at 13:30Found the solution on my own just use $less$colon$less$.MODULE$.refl()
instead of Predef.>conforms()
QUESTION
I have a function filter'
:
ANSWER
Answered 2021-Jan-08 at 02:40filter' ... (x ∷ filter' ... xs) | x ≡ᵇ id)
means that the evaluation of
this function is stuck on the test x ≡ᵇ id
.
To have it reduce, you would typically use with x ≡ᵇ id
. But you've already
done that! Yes, but the with
you used targeted the inner filter
that was
stuck at the time. Once it got unstuck, it computed enough to emit x ∷ _
and
that got the outer filter
stuck on the second test (that happens to be equal
to the first one).
The idiomatic way to deal with this is via the inspect
idiom
that will allow you to, in a single with
, get your hands on not only the
result of x ≡ᵇ id
but also a proof that the result was computed from this
expression. Once you reach the point where the outer filter
is stuck, you
can simply rewrite
by this equation and you should then be able to see
the function compute just enough that it will be possible to call the
induction hypothesis.
QUESTION
I defined allButLast
this way:
ANSWER
Answered 2020-Nov-30 at 09:24I suggest the following solution:
QUESTION
I have the function:
...ANSWER
Answered 2020-Nov-16 at 21:33I suggest the following solution:
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