From 1d5041ff7bf92458d6d07ac6a03f2747dce9b9b1 Mon Sep 17 00:00:00 2001
From: Case Duckworth
Date: Thu, 21 Mar 2024 22:34:12 -0500
Subject: Refactor eval

Localize stuff and also break out specials
---
 eval.lua | 75 +++++++++++++++++++++++++++++++++++++++++-----------------------
 1 file changed, 48 insertions(+), 27 deletions(-)

diff --git a/eval.lua b/eval.lua
index 9b1c315..39a5bbe 100644
--- a/eval.lua
+++ b/eval.lua
@@ -1,13 +1,12 @@
 --- lam.eval
 
-local eval = {}
 local base = require "base"
 local type = require "type"
 local isNull, isList, isa, List, Cons =
 	type.isNull, type.isList, type.isa, type.List, type.Cons
 local unpack = table.unpack or unpack
 
-function eval.Env (inner, outer)
+local function Env (inner, outer)
 	local mt = {
 		__type = "Environment",
 		__index = outer,
@@ -25,7 +24,7 @@ function eval.Env (inner, outer)
 	return setmetatable(inner, mt)
 end
 
-function eval.Proc (params, body, env)
+local function Proc (params, body, env)
 	local v = {
 		params = params,
 		body = body,
@@ -42,18 +41,51 @@ function eval.Proc (params, body, env)
 					p, a = p.cdr, a.cdr
 				end
 				local b = self.body
-				local e = eval.Env(inner, self.env)
+				local e = Env(inner, self.env)
 				while not isNull(b.cdr) do
-					eval.eval(b.car, e)
+					eval(b.car, e)
 					b = b.cdr
 				end
-				return eval.eval(b.car, e)
+				return eval(b.car, e)
 			end,
 	}
 	return setmetatable(v, mt)
 end
 
-function eval.eval (x, env)
+local specials = {
+	quote =
+		function (args, env)
+			return args.car
+		end,
+	define =
+		function (args, env)
+			rawset(env, args.car, eval(args.cdr.car, env))
+			return nil
+		end,
+	lambda =
+		function (args, env)
+			return Proc(args.car, args.cdr, env)
+		end,
+	["set!"] =
+		function (args, env)
+			env[args.car] = eval(args.cdr.car, env)
+			return nil
+		end,
+	["if"] =
+		function (args, env)
+			local test, conseq, alt =
+				args.car, args.cdr.car, args.cdr.cdr.car
+			if eval(test)
+			then return eval(conseq)
+			else return eval(alt)
+			end
+		end,
+}
+-- Aliases
+specials.lam = specials.lambda
+specials.def = specials.define
+
+local function eval (x, env)
 	env = env or base.env
 	if isa(x, "Symbol") then
 		return env[x]
@@ -61,29 +93,14 @@ function eval.eval (x, env)
 		return x
 	else
 		local op, args = x.car, x.cdr
-		if op == "quote" then
-			return args.car
-		elseif op == "define" or op == "def" then
-			rawset(env, args.car, eval.eval(args.cdr.car, env))
-			return nil
-		elseif op == "set!" then
-			env[args.car] = eval.eval(args.cdr.car, env)
-		elseif op == "lambda" or op == "lam" then
-			return eval.Proc(args.car, args.cdr, env)
-		elseif op == "if" then
-			assert(not isNull(args.cdr), "Malformed 'if'")
-			local test, conseq, alt =
-				args.car, args.cdr.car, args.cdr.cdr.car
-			if eval.eval(test)
-			then return eval.eval(conseq)
-			else return eval.eval(alt)
-			end
+		if specials[op] then
+			return specials[op](args, env)
 		else		-- procedure
-			local proc = eval.eval(op, env)
+			local proc = eval(op, env)
 			local params = {}
 			local a = args
 			while a.cdr do
-				table.insert(params, eval.eval(a.car, env))
+				table.insert(params, eval(a.car, env))
 				a = a.cdr
 			end
 			return proc(List(params))
@@ -92,4 +109,8 @@ function eval.eval (x, env)
 end
 
 ---
-return eval
+return {
+	Env = Env,
+	Proc = Proc,
+	eval = eval,
+}
-- 
cgit 1.4.1-21-gabe81