Comment author: @Octachron

Correction:
The compiler simply forgets the name of type variable starting with a capital letter.

Compare

let f (x:'id_arg) = x;;

val f : 'id_arg -> 'id_arg =

with

let f (x:'Id_arg) = x;;

val f : 'a -> 'a =

Comment author: @garrigue

Fixed in trunk at revision 16489.

Didn't know that variable names could start with a capital letter...

Comment author: talex

Might be worth extending the error message in this case with a "- did you mean `A_name"?

Comment author: @gasche

I extended the error message with a hint as you suggest.

Note that while

type t = [ 'Foo | 'Bar ]

(or any combination with a ' and a `)
will get you the hint, just writing

type t = [ 'Foo ]

is caught as a syntax error at an earlier stage, and does not benefit from the same treatment. We're thinking about general improvements on syntax error reporting, so I won't spend time on this error specifically.

Comment author: talex

Thanks!