016 fold unknown branch

✓ Passing Passing: the compiler rejects this program as expected.

Code

// An arm the fold does not answer refuses: `| node` and `| null` are the
// whole vocabulary.
import std/tree

std/tree:node(Node) { item: i64, left: ?Node }

pub tor mk { } -> *Node<owned!>
mk = if(true)
    | then |> std/tree:mint(Node) { item: 1, left: null }: h -> h
    | else -> null

mk(): t
|> std/tree:fold(t, as: i64): c
    | node n -> n.item + n.left
    | leaf -> 0
|> std/tree:dispose(t): _

input.k

Actual compiler output

error[KORU184]: std/tree:fold(t): the 'leaf' arm is not one a fold answers — `| node <name> -> <expr>` and `| null -> <expr>` are the whole vocabulary
  --> tests/regression/600_STDLIB/682_TREE/682_016_fold_unknown_branch/input.k:13:1

Must contain:

KORU184

Flows

flow ~node click a branch to expand · @labels scroll to their anchor

node (Node, source: item: i64, left: ?Node)

subflow ~mk click a branch to expand · @labels scroll to their anchor

if (true)

flow ~mk click a branch to expand · @labels scroll to their anchor

Test Configuration

MUST_ERROR

← 015 fold bare binding 017 fold unresolvable binding →