Method cond

src/expr/src/interpret.rs:542–544

(&self, cond: Self::Summary, then: Self::Summary, els: Self::Summary)

    }

    fn cond(&self, cond: Self::Summary, then: Self::Summary, els: Self::Summary) -> Self::Summary {
        self.evaluator.cond(cond, then, els)
    }
}

/// A unary function we've added special-case handling for; including: