         }
     }
 
-    // Note: thrown error is always a SymbolError
+    // Note: thrown error is always a LayoutError
     private var _settingUpExpressions = false
     private var _expressionsSetUp = false
     private func setUpExpressions() throws {

    private(set) var _originalExpressions: [String: String]
    var _parameters: [String: RuntimeType]

    private var _setupComplete = false
    private func completeSetup() throws {
        guard !_setupComplete else { return }

        }
        try completeSetup()
        for symbol in expressions.keys {
            try LayoutError.wrap({ try setUpExpression(for: symbol) }, for: self)
        }

        #if arch(i386) || arch(x86_64)
