Term initialization is partial.

prototype/Doubt/Syntax.swift

@@ -36,33 +36,49 @@ public enum Term: CustomDebugStringConvertible, CustomDocConvertible, CustomStri
 	// MARK: JSON representation.
 
 	/// Constructs a Term representing the `JSON` in a file at `path`.
-	public init(path: String, JSON: Doubt.JSON) {
+	public init?(path: String, JSON: Doubt.JSON) {
+		struct E: ErrorType {}
+		func die<A>() throws -> A {
+			throw E()
+		}
+		do {
 			switch JSON.dictionary?["key.substructure"] {
 			case let .Some(.Array(a)):
-			self = .Roll(.Group(.Roll(.Literal(path)), a.map(Term.init)))
+				self = .Roll(.Group(.Roll(.Literal(path)), try a.map { try Term(JSON: $0) ?? die() }))
 			default:
-			self = .Empty
+				return nil
+			}
+		} catch _ {
+			return nil
 		}
 	}
 
 	/// Constructs a Term representing `JSON`.
-	public init(JSON: Doubt.JSON) {
+	public init?(JSON: Doubt.JSON) {
+		struct E: ErrorType {}
+		func die<A>() throws -> A {
+			throw E()
+		}
+		do {
 			switch JSON.dictionary {
 			case let .Some(d) where d["key.name"] != nil && d["key.substructure"] != nil:
 				let name = d["key.name"]?.string ?? ""
 				let substructure = d["key.substructure"]?.array ?? []
 				switch d["key.kind"]?.string {
 				case .Some("source.lang.swift.decl.class"), .Some("source.lang.swift.decl.extension"):
-				self = .Group(.Literal(name), substructure.map(Term.init))
+					self = .Group(.Literal(name), try substructure.map { try Term(JSON: $0) ?? die() })
 
 				case .Some("source.lang.swift.decl.function.method.instance"), .Some("source.lang.swift.decl.function.free"):
-				self = .Assign(name, .Abstract([], substructure.map(Term.init)))
+					self = .Assign(name, .Abstract([], try substructure.map { try Term(JSON: $0) ?? die() }))
 
 				default:
-				self = .Empty
+					return nil
 				}
 			default:
-			self = .Empty
+				return nil
+			}
+		} catch _ {
+			return nil
 		}
 	}
 }

prototype/doubt-swift/main.swift

@@ -13,7 +13,7 @@ extension Term {
 			.map(Structure.init)
 			.map({ $0.dictionary })
 			.map(toAnyObject)
-			.flatMap({ JSON(object: $0).map { Term(path: path, JSON: $0) } }) else { return nil }
+			.flatMap({ JSON(object: $0).flatMap { Term(path: path, JSON: $0) } }) else { return nil }
 		self = term
 	}
 }