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Questions tagged [idris2]

27 questions
4
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1 answer

Can I avoid lower-case global variables being shadowed in types?

The following code compiles okay in Idris2: C : Nat C = 2 claim : C = 2 claim = Refl but it fails if C is not capitalized: c : Nat c = 2 claim : c = 2 claim = Refl The error message is Warning: We are about to implicitly bind the following…
haskell looks great
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3
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1 answer

Idris totality check

I am compiling the following simple program using Idris2. import Data.Fin %default total negate : {k:_} -> Fin k -> Fin k subt : {k:_} -> Fin k -> Fin k -> Fin k add : {k:_} -> Fin k -> Fin k -> Fin k mult : {k:_} -> Fin k -> Fin k -> Fin k mult…
haskell looks great
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What does the 0 or 1 before a parameter name mean in Idris?

I've seen it here and there in Idris source code, but I have yet to find an explanation for what it means. The closest I've gotten is finding that it's called RigCount in the syntax reference. But what is it? test : (0 a : b) -> b test x = x -- …
Aron
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How should I sum doubles in Idris?

I don't understand why the following does not work: Main> 2.1 + 2.3 Error: Can't find an implementation for FromDouble Integer. (Interactive):1:1--1:4 1 | 2.1 + 2.3 ^^^ It works with integers, and if I understand the docs correctly, it…
lxnv
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Idris 2 analog to Agda's `rewrite` that also changes types of bindings in the environment

Suppose I have a theorem foo : (n : _) -> (f : Fin (n + 0)) -> ... foo n f = ?goal and it'd really benefit me if I could use f in contexts where Fin n is expected (and I really mean the precise term f instead of, say, replace (plusZeroRightNeutral…
0xd34df00d
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How to deal with "Error: Multiple solutions found"?

I'm trying to build a set datatype. mutual data Set : Type -> Type where Nil : Eq a => Set a (::) : Eq a => (x : a) -> (s : Set a) -> {auto _ : contains x s = False} -> Set a contains : Eq a => a -> Set a -> Bool contains x [] =…
magras
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1 answer

How to use interfaces with parameterized tuple?

I have Coord function that transforms an n-dimensional size to the type of coordinates bounded by given size: Coord [2,3] = (Fin 2, Fin 3). import Data.Fin import Data.List Size : Type Size = List Nat Coord : Size -> Type Coord [] = () Coord s@(_…
magras
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2
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1 answer

How to implement `Show` interface for parameterized tuple?

I have Coord function that transforms an n-dimensional size to the type of coordinates bounded by given size: Coord [2,3] = (Fin 2, Fin 3). import Data.Fin import Data.List Size : Type Size = List Nat Coord : Size -> Type Coord [] = () Coord s@(_…
magras
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Main.case block in case block in _ is not accessible in this context

Walking through the format string example in the TDD of Idris2, and trying to do my own version of a format string. Here is what has worked: data ShowableFmt = NatFmt | CharFmt | DoubleFmt data CallableFmt = ShwFmt ShowableFmt | StrFmt data Fmt =…
Clément Dato
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2 answers

Importing from the contrib library fails

I'm following the TDD book in Idris 2, and the online documentation gives the following advice: For the VList view in the exercise 4 after Chapter 10-2 import Data.List.Views.Extra from contrib library. So I put this import in a source file…
MB-F
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How to write a pure function in idris2 FFI?

The idris2 has the following example for FFI, which adds two integers in C: #include int add(int x, int y) { return x+y; } (small.c) I followed the steps, and after linking: gcc -shared smallc.c -o libsmall.so and indeed the foreign…
thor
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function with no parameter and the main function?

Book "Type-driven Development with Idris" page 52 has 2.5 Summary ... Function types have one or more input types and one output type. The entry point to an Idris program is the main function, which must have type IO (), and be defined in the…
Gqqnbig
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1 answer

Can we express () in terms of a Record in Idris?

Can we express () i.e Unit type in terms of a Record in Idris ?
Rocky
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Why does Idris think my type parameter k is of type Type?

Sorry I couldn't think of a less confusing way to put this. I'm trying to build something like a map that can be safely accessed without returning a maybe, because all of its keys are contained in its type and querying for a key that isn't contained…
Aron
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Updating a dependently typed field without updating what it depends on

I'd like to use record update syntax to update a dependently-typed field without also changing the field it depends on. So I'd like to have Idris 2 evaluate the other field, and realize everything is kosher. Is this doable? Here's a concrete minimal…
Cactus
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