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Document mapping a term into a diff.

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Rob Rix 2015-10-23 11:40:03 -04:00
parent 180cc41f6c
commit 383b20bb31
1 changed files with 3 additions and 0 deletions
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prototype/Doubt/Interpreter.swift
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@ -42,6 +42,9 @@ public struct Interpreter<Term: CofreeType> {
/// Diff `a` against `b`, if comparable. /// Diff `a` against `b`, if comparable.
private func recur(a: Term, _ b: Term) -> Diff? { private func recur(a: Term, _ b: Term) -> Diff? {
// If both terms are equal, we don’t need to bother diffing.
//
// In that case, zip the two terms together (to pair their annotations), and then map the resulting `Term` (which, since the terms are equal, will be non-nil) into a `Diff`.
if equal(a, b) { return hylo(Diff.Roll, Cofree.eliminate)(Term.zip(a, b)!) } if equal(a, b) { return hylo(Diff.Roll, Cofree.eliminate)(Term.zip(a, b)!) }
guard comparable(a, b) else { return nil } guard comparable(a, b) else { return nil }