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I am using Ocaml of version 4. When I define interactively some type, the interpreter prints out string representation of the type immediately after that:
# type foo = Yes | No;; <-- This is what I entered
type foo = Yes | No <-- This is what interpreter bounced
But after I type more definitions, sometimes I want to see the text representation of the type again.
In Haskell, I could type ":t foo".
How can I do this in Ocaml?
396
The type 'a is a type variable, and stands for any given type. The reason why sort can apply to lists of any type is that the comparisons (=, <=, etc.) are polymorphic in OCaml: they operate between any two values of the same type. This makes sort itself polymorphic over all list types.
OCaml doesn't have a return keyword — the last expression in a function becomes the result of the function automatically.
Note that :: is technically a type constructor which is why you can use it in both patterns and expressions.
In a terminal window, type utop to start the interactive OCaml session, commonly called the toplevel. Press Control-D to exit the toplevel. You can also enter #quit;; and press return. Note that you must type the # there: it is in addition to the # prompt you already see.
In utop you can use the #typeof directive:
#typeof "list";;
type 'a list = [] | :: of 'a * 'a list
You can put values and types inside double quotes:
let t = [`Hello, `World];;
#typeof "t";;
val t : ([> `Hello ] * [> `World ]) list
P.S. And even better solution would be to use merlin.
157
As far as I know, there is actually no way in Ocaml to retrieve type information under a string form
You'll have to build a pattern matching for each of your type
type foo = Yes | No;;
let getType = function
|Yes -> "Yes"
|No -> "No"
;;
let a = Yes;;
print_string (getType a);;
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