From 5a911ff0009d353cd278cc3371d50f54f5742a5c Mon Sep 17 00:00:00 2001
From: pingu <nor@acorneroftheweb.com>
Date: Tue, 25 Nov 2025 19:47:14 +0100
Subject: [PATCH] Baba

---
 3or4/Interpreter/Self.hs | 42 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/3or4/Interpreter/Self.hs b/3or4/Interpreter/Self.hs
index 474da97..b09ea02 100644
--- a/3or4/Interpreter/Self.hs
+++ b/3or4/Interpreter/Self.hs
@@ -5,6 +5,8 @@ module Interpreter.Self where
 import Chi
 import Interpreter.Haskell
 
+-- Task 3
+
 mapExp :: Exp
 mapExp = parse
   "\\f. rec map = \\xs. case xs of \
@@ -57,3 +59,43 @@ substExp =
         \ ; Rec(x, e') -> if (equal x var) Rec(x,e') Rec(x,subst e')\
         \ ; Case(e',bs) -> Case(subst e', map (substBr subst var) bs) \
         \ }"
+
+-- Task 4
+
+lookupExp :: Exp
+lookupExp =
+  subst (Variable "if") ifExp .
+  subst (Variable "equal") equalExp $ parse
+  "\\c. rec lookup = \\xs. case xs of \
+  \ -- TODO: Fix for Nil() \
+  \ { Cons(b,bs) -> \
+  \     case b of \
+  \       { Branch(c', bs, e') -> if (equal c c') Pair(bs,e') (lookup bs) } \
+  \ }"
+
+substsExp :: Exp
+substsExp =
+  subst (Variable "subst") substExp $ parse
+  "rec substs = \\xs. \\vs. \\e'. case xs of \
+  \ { Nil() -> case vs of { Nil() -> e' } \
+  \ ; Cons(x,xs) -> case vs of { Cons(v,vs) -> subst x v (substs xs vs e') }\
+  \ }"
+
+evalExp :: Exp
+evalExp =
+  subst (Variable "map") mapExp .
+  subst (Variable "lookup") lookupExp .
+  subst (Variable "substs") substsExp .
+  subst (Variable "subst") substExp $ parse
+  "rec eval = \\e. case e of \
+  \ { Lambda(x,e) -> Lambda(x,e) \
+  \ ; Apply(e1,e2) -> case eval e1 of \
+  \    { Lambda(x,e) -> eval (subst x (eval e2) e) } \
+  \ ; Rec(x,e) -> eval (subst x Rec(x,e) e) \
+  \ ; Const(c,es) -> Const(c, map eval es) \
+  \ ; Case(e,bs) -> case eval e of \
+  \     { Const(c,vs) -> case lookup c bs of \
+  \        { Pair(xs,e') -> eval (substs xs vs e') } \
+  \     } \
+  \ ; Var(x) -> Var(x) \
+  \ }"