Recs.
Updated
Specs
Pros
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 Compiles to executables or to JavaScript/Node, and other targets.
Idris comes with two code generators out of the box: one for executables, via your platform's C compiler, and one that can produce JavaScript code for the browser or for Node.js. There's an code generator API for writing one's one code generator; a number of third-party projects exist that give you, among others, WebAssembly, Erlang, Java, PHP, Python, Ruby, etc.
Cons
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.