!import "prelude" !Local
!import "io" !Local
!import "view" !Local

-- View Contracts inside IO continuations
-- Run with:
--
--   tricu eval demos/viewContracts/io-continuation.tri --io -f decode
--
-- Checked IO evaluation instruments continuation bodies once from source
-- annotations. The IO runtime still executes ordinary interaction-tree actions;
-- the returned continuations already contain the checked-exec guard boundaries.

requireNonEmpty = (xs :
  lazyBool
    (_ : guardFail)
    (_ : guardOk xs)
    (emptyList? xs))

NonEmptyList elem = viewGuarded (viewList elem) requireNonEmpty

acceptNames xs@(NonEmptyList String) =@String "accepted"

useHandler handler@(Fn [(NonEmptyList String)] String) xs@(List String) =@String
  handler xs

-- The IO action yields an empty list. The higher-order boundary requires a
-- handler that accepts NonEmptyList String, so the continuation-internal pure
-- call fails before returning the next IO value.
main = io (bind (pure []) (xs : pure (useHandler acceptNames xs)))