017 fold unresolvable binding

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

Code

// `fold` on a binding whose node kind can't be resolved refuses with the
// same provenance teaching `dispose` gives.
import std/tree

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

pub tor mk { } -> i64
mk = if(true)
    | then -> 1
    | else -> 0

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

input.k

Actual compiler output

error[KORU184]: std/tree:fold(t): can't resolve which node kind 't' is — bind it from a std/tree:mint, a tor returning *X<owned!>, or declare the parameter `*X<...>` for a node-registered X
  --> tests/regression/600_STDLIB/682_TREE/682_017_fold_unresolvable_binding/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

← 016 fold unknown branch 018 fold step chain arm →