From c96333038485afd78bcd15539dcba89a2d3fb328 Mon Sep 17 00:00:00 2001
From: mehbark <terezi@pyrope.net>
Date: Sun, 8 Dec 2024 21:31:53 -0500
Subject: [PATCH] prepublish

---
 src/lib.rs | 50 ++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 38 insertions(+), 12 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index a8ad3a2..939c2fc 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -15,7 +15,7 @@ use thiserror::Error;
 /// A representation of a term of the
 /// [lambda calculus](https://en.wikipedia.org/wiki/Lambda_calculus), using
 /// [de Bruijn indices](https://en.wikipedia.org/wiki/De_Bruijn_index).
-#[derive(Debug, PartialEq, Eq)]
+#[derive(Debug, Clone, PartialEq, Eq)]
 pub enum LC {
     /// A lambda abstraction; binds a new variable.
     Abs(Rc<LC>),
@@ -111,7 +111,7 @@ impl fmt::Display for LC {
 
 /// A representation of a term of the
 /// [SKI combinator calculus](https://en.wikipedia.org/wiki/SKI_combinator_calculus).
-#[derive(Debug, PartialEq, Eq)]
+#[derive(Debug, Clone, PartialEq, Eq)]
 pub enum SKI {
     /// The S (substitution) combinator.
     ///
@@ -162,12 +162,6 @@ impl fmt::Display for SKI {
     }
 }
 
-#[derive(Debug, PartialEq, Eq)]
-pub enum Iota {
-    Iota,
-    App(Rc<Iota>, Rc<Iota>),
-}
-
 #[derive(Debug, Error, PartialEq, Eq)]
 pub enum SKICompileError {
     #[error("LC term has a free variable")]
@@ -179,9 +173,41 @@ impl TryFrom<LC> for SKI {
     type Error = SKICompileError;
 
     fn try_from(term: LC) -> Result<Self, Self::Error> {
-        if term.has_free() {
-            return Err(SKICompileError::FreeVar);
-        }
-        todo!()
+        use SKI::{App, I, K, S};
+        Ok(match term {
+            LC::Abs(x) => match &*x {
+                LC::Abs(y) => match &**y {
+                    // x
+                    LC::Var(1) => K,
+                    LC::Abs(z) => match z {
+                        LC::App(_, _) => todo!(),
+                        _ => todo!(),
+                    },
+                    _ => todo!(),
+                },
+                LC::Var(0) => I,
+                _ => todo!(),
+            },
+            LC::App(f, x) => {
+                let f: SKI = f.try_into()?;
+                let x: SKI = x.try_into()?;
+                f.app(x)
+            }
+            LC::Var(_) => Err(SKICompileError::FreeVar)?,
+        })
     }
 }
+
+impl TryFrom<Rc<LC>> for SKI {
+    type Error = SKICompileError;
+
+    fn try_from(value: Rc<LC>) -> Result<Self, Self::Error> {
+        (*value).clone().try_into()
+    }
+}
+
+#[derive(Debug, PartialEq, Eq)]
+pub enum Iota {
+    Iota,
+    App(Rc<Iota>, Rc<Iota>),
+}