Problem at matching 'None'

[angelpopov]

I am am trying to create function that returns error message if function params differ.

  (declare ha ( (Optional Shard) -> Shard -> (Optional String)))
  (define (ha old-shard shard)
    (match old-shard
      ((Some old) (if (== old shard) None
                      (Some (mconcat (make-list "Expected" (into old) " received:" (into shard))))))
      ( None None)))

CL-USER> (coalton:coalton-toplevel   
(coalton:declare ha (
 (coalton:Optional coalton:integer) coalton:-> coalton:integer coalton:-> (coalton:Optional coalton:String)))
  (coalton:define (ha old-shard shard)
    (coalton:match old-shard
      ((coalton:Some old) (coalton:if coalton:true coalton:None
                      (coalton:Some "err")))
      ( coalton:None coalton:None)))
)

but get

 10 |        (COALTON:NONE COALTON:NONE))))
    |         ^^^^^^^^^^^^ Expected type '(COALTON:OPTIONAL COALTON:STRING)' but got '(COALTON:OPTIONAL COALTON:INTEGER)'

Seems that type of None was not inferred correctly, so tried to specify the expected type

CL-USER> (coalton:coalton-toplevel 
  (coalton:declare ha (
   (coalton:Optional coalton:integer) coalton:-> coalton:integer coalton:-> (coalton:Optional coalton:String)))
  (coalton:define (ha old-shard shard)
    (coalton:match old-shard
      ((coalton:Some old) (coalton:if coalton:true coalton:None
                      (coalton:Some "err")))
      ( coalton:None (coalton:the (coalton:Optional coalton:String) coalton:None))))
)

but then

    |
 11 |         (COALTON:THE (COALTON:OPTIONAL COALTON:STRING) COALTON:NONE)))))
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Declared type '(COALTON:OPTIONAL COALTON:STRING)' does not match inferred type '(COALTON:OPTIONAL COALTON:INTEGER)'
   [Condition of type COALTON-IMPL/TYPECHECKER/BASE:TC-ERROR]

What I am missing?

[angelpopov]

Oh, it matches on (None) - in brackets.

  (declare ha ( (Optional Shard) -> Shard -> (Optional String)))
  (define (ha old-shard shard)
    (match old-shard
      ((Some old) (if (== old shard) None
                      (Some (mconcat (make-list "Expected" (into old) " received:" (into shard))))))
      ( (None) None)))

[stylewarning]

Yes that's correct. Constructor patterns are always wrapped in parens.