unison/unison-src/errors/ex1.u

use Optional None Some

foo : Optional a -> [a]
foo = cases
  None -> []
  Some a -> [a]

"hello" `Sequence.cons` foo (Some 3)

-- Sequence.cons has type `a -> [a] -> [a]`
--  `a` was determined to be `Text` because "hello" had type `Text`.
-- Therefore `foo (Some 3)` was checked against `[Text]`
-- but it actually had type `[Nat]`. Use `> why err1` for more detail.
-- type Extractor v loc a = Note v loc -> Maybe a
-- do
--   e <- errorTerm
--   b <- isFunctionCall
--   if b then do
        --


-- in reply to `> why err1`:
-- `foo` has type `Optional a -> [a]`
--   `a` was determined to be `Nat` because
--   `Some 3` has type `Optional Nat`. Use `> why err2` for more detail

-- in reply to `> why err2`:
-- `Some` has type `a -> Optional a`
--   `a` was determinewd to be `Nat` because `3` has type `Nat`

x = 3

and x 4
------------- generic synthesizeApp possibility
-- `and` has type `Boolean -> Boolean -> Boolean`
--    .. (no typevars to explain, so skip)
-- Therefore `3` was checked against `Boolean`,
-- but it actually had type `Nat`.

------------- specialized "and" possibility
-- The arguments to `and` must be of type `Boolean`,
-- but `x` has type `Nat`. Use `> why err1` for more detail.

and 3 4
-- but the literal `3` has type `Nat`.

match 3 with
  3 -> "text"
  4 -> 4.0