enters-a-copy-whose-argument-reads-to-no-bare-symbol-when-deferring.yaml

# SPDX-FileCopyrightText: Copyright (c) 2025 Objectionary.com
# SPDX-License-Identifier: MIT
---
# yamllint disable rule:line-length
# An entry that says 'defer: true' defers only a copy one of whose arguments
# reads to a bare symbol (#1892). Here 'Φ.items.tail' reads to an object that
# knows its 'next', so the lenient join enters the copy as it did before
# (#1885): it morphs its φ, fires what it comes to, and joins two symbols. No
# 'deferred' line is written and no symbol is minted for the copy.
symbolic: |
  - λ: L_fork
    morph:
      𝑛1: $.a
      𝑛2: $.b
    join:
      𝑛3: [𝑛1, 𝑛2]
    lenient: true
    defer: true
    𝑛: ⟦ φ ↦ 𝑛3 ⟧
location: 'Q.y'
input: '⟦ step(tup) ↦ ⟦ φ ↦ tup.next ⟧, items ↦ ⟦ tail ↦ ⟦ next ↦ ⟦ φ ↦ ⟦ λ ⤍ 𝜎1 ⟧ ⟧ ⟧ ⟧, y ↦ ⟦ a ↦ ⟦ λ ⤍ 𝜎2 ⟧, b ↦ Φ.step( tup ↦ Φ.items.tail ), λ ⤍ L_fork ⟧.φ ⟧'
result: '𝜎3:λ'
protocol: |
  𝕄(Φ.y):
    𝔼(L_fork):
      𝑛1·1 := 𝜎2:λ  # 𝕄(ξ.a)
      𝕄(Φ.a🌵1):
        𝑛·1·1 := Φ.step( tup ↦ Φ.items.tail )
      𝑛2·1 := 𝑛·1·1  # 𝕄(ξ.b)
      𝑛2·1 := 𝜎1:λ:φ  # 𝕄(𝑛2.φ)
      𝑛2·1 := 𝑛2·1  # 𝔼(𝑛2)
      𝔻(𝜎3:λ) ∈ { 𝔻(𝜎2:λ), 𝔻(𝜎1:λ) }
      𝑛3·1 := 𝜎3:λ  # [𝑛1, 𝑛2]
      𝑛·1·2 := 𝜎3:λ:φ  # 𝑛
      𝑛·1·3 := 𝜎3:λ:φ  # 𝕄(𝑛·1·2)