| use std::ops; | |
| use crate::Expression; | |
| /// Church encoded natural numbers. | |
| pub struct Natural(Expression); | |
| impl Natural { | |
| pub fn expression(&self) -> &Expression { | |
| &self.0 | |
| } | |
| } | |
| impl From<u64> for Natural { | |
| fn from(n: u64) -> Self { | |
| let succ = λ!{n.λ!{f.λ!{x.γ!(f, γ!(γ!(n, f), x))}}}; | |
| let mut e = λ!{f.λ!{x.x}}; | |
| for _ in 0..n { | |
| e = app!({&succ}, {&e}).normalize(false); | |
| } | |
| Natural(e) | |
| } | |
| } | |
| impl Into<u64> for Natural { | |
| fn into(self) -> u64 { | |
| unimplemented!(); | |
| } | |
| } | |
| impl ops::Add for Natural { | |
| type Output = Self; | |
| fn add(self, other: Self) -> Self { | |
| let add = λ!{m.λ!{n.λ!{f.λ!{x.γ!(γ!(m,f),γ!(γ!(n,f),x))}}}}; | |
| Natural(γ!(γ!({add},{self.0}),{other.0}).normalize(false)) | |
| } | |
| } | |
| impl ops::Mul for Natural { | |
| type Output = Self; | |
| fn mul(self, other: Self) -> Self { | |
| let mul = λ!{m.λ!{n.λ!{f.λ!{x.γ!(γ!(m,γ!(n,f)),x)}}}}; | |
| Natural(γ!(γ!({mul},{self.0}),{other.0}).normalize(false)) | |
| } | |
| } | |
| #[cfg(test)] | |
| mod tests { | |
| use super::*; | |
| #[test] | |
| fn add() { | |
| assert_eq!(Natural::from(5).expression(), | |
| (Natural::from(2) + Natural::from(3)).expression()); | |
| } | |
| #[test] | |
| fn multiply() { | |
| assert_eq!(Natural::from(6).expression(), | |
| (Natural::from(2) * Natural::from(3)).expression()); | |
| } | |
| } |
nixpulvis/lalrpop-lambda
