When comparing Idris vs Crystal, the Slant community recommends Crystal for most people. In the question“What programming language has the best syntax?” Crystal is ranked 9th while Idris is ranked 17th.
Ranked in these QuestionsQuestion Ranking
Pro Full dependent types
Idris not only has support for type classes, but is a fully dependently typed language, giving you the full power to statically verify your code.
Pro Domain driven design and type driven development
Because of full dependent types in Idris, the programmer can focus more on modelling the domain with types and waste less time fixing common bugs that the type checker will catch. Dependent types help apply type driven development and a lot of code auto generation, making the compiler and type checker an ally in developing working software instead of just getting in the way.
Pro Elegant syntax as Ruby
Pro Fast performance
Pro Has co-routine
Pro Compiles to native binary
Con Not widely used
Con Not widely used
Con Weaker type inference
As type inference is undecidable for dependently-typed languages, Idris cannot offer the full type inference that Haskell supports, and so more type annotations will be needed.
Con Different semantics from Haskell
Idris, while similar to Haskell, has strict semantics, which may cause some confusion if your backend is done in Haskell. If using Idris, it would make sense to do the backend in Idris as well, if not for the fact that Idris currently has fewer libraries available for web development than Haskell.
Con Aruguably no better than a meme language
The elitest attitudes in the community are unwarrented. Not recommendable for production use. Poor error messages, odd compiler errors, poorly documented behavior, etc..
Con Small community
In regards to its age and already past 1.0, the community is still too small.
Con Not cross-platform
No official Windows support.
Con A language only Ruby fans can love
Con Slow compilation
Con No parallelism (yet)
Not actual anymore.