How can I ask for the type class of a variable?

Question

I'm trying to learn ReasonML, and I'm doing some koans to help me with that task. One of the koans I'm trying to code is about asking for the type of a list after converting it to an array. I know that there are operators in some languages like Haskell (:t) where we can ask for the type of a variable. Is there any equivalent to :t for ReasonML? Or it shouldn't make sense to check if Array.of_list returns an array because the compiler ensures that...

Answer 1

I don't know much about Reason, but utop (an improved OCaml REPL) provides the #typeof directive to inspect the type of an expression:

let a = 42;;
val a : int = 42

#typeof "a";;
val a : int

Note that this is only a REPL tool. In OCaml, types are not available on runtime: they are stripped during compilation. You can learn more about the OCaml compilation process here.

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As pointed out by @Rizo in the comments, there also is the #show directive, which is even available in the standard OCaml REPL:

let a = 43;;
val a : int = 43

#show a;;
val a : int