moving forward

lisp.lua

@@ -1,25 +1,114 @@
 #!/usr/local/bin/lua-5.1
 
-my={}
-my.read = function (str)
-  local function numberp (char)
-    tmp = string.byte(char)
-    if tmp ~= nil and tmp > 47 and tmp < 58 then
-      return true
-    else
-      return false
+List = {}
+local list_meta = {}
+function List.cons (a, b)
+  return {car=a,cdr=b}
+end
+function List.new (...)
+  l = arg
+  l.c = 1
+  li = List.list(l)
+  setmetatable(li,list_meta)
+  return li
+end
+function List.list(l)
+  if l.c <= l.n then
+    a = l[l.c]
+    l.c = l.c + 1
+    return List.cons(a, List.list(l))
+  else
+    return nil
+  end
+end
+function List.tostring(lst)
+  p = lst
+  buf=""
+  while p ~= nil do
+    buf = buf .. to_s(p.car) 
+    if p.cdr ~= nil then
+      buf = buf .. " "
     end
+    p = p.cdr
+  end
+  return "(".. buf ..")"
+end
+function List.eval(a, b)
+  return Interpreter.apply(Interpreter.eval(List.first(a)),List.map(function (a) return Interpreter.eval(a, b); end,List.rest(a)))
+end
+function List.first(a)
+  return a.car
+end
+function List.rest(a)
+  p = a.cdr
+  if p ~= nil then
+    setmetatable(p, list_meta)
+  end
+  return p
+end
+function List.map(f, lst)
+  if lst ~= nil then
+    return List.cons(f(List.first(lst)), List.map(f, List.rest(lst)))
+  else
+    return lst
+  end
+end
+list_meta.__tostring = List.tostring
+list_meta.__index = List
+
+Symbol = {}
+local symbol_meta = {}
+function Symbol.new (s)
+  m = {name=s}
+  setmetatable(m,symbol_meta)
+  return m
+end
+function Symbol.tostring (s)
+  return s.name
+end
+function Symbol.eval (s)
+  return {primitive = true, name=s.name}
+end
+symbol_meta.__tostring = Symbol.tostring
+symbol_meta.__index = Symbol 
+
+Interpreter = {}
+function Interpreter.to_s(thing) 
+  if thing == nil then
+    return "nil"
+  elseif type(thing) == "number" then
+    return ""..thing
+  else
+    return thing:tostring()
   end
-  for w=1,string.len(str) do
-    if numberp(string.sub(str,w,w+1)) then
-      buf={}
-      while numberp(string.sub(str,w,w+1)) do
-        table.insert(buf, string.sub(str,w,w+1))
-        w = w + 1
-      end
-      print(w)
+end
+function Interpreter.eval(thing, env)
+  if thing == nil then
+    return nil
+  elseif type(thing) == "number" then
+    return thing
+  else
+    return thing:eval(env)
+  end
+end
+function Interpreter.apply(fn, args)
+  if fn.primitive ~= nil then
+    return Interpreter.apply_prim(fn.name, args)
+  end
+end
+function Interpreter.apply_prim(fn, args)
+  if fn == "+" then
+    p = args
+    ac = 0
+    while p ~= nil do
+      ac = ac + List.first(p)
+      p = List.rest(p)
     end
+    return ac
   end
 end
 
-my.read("109")
+l1 = List.new(Symbol.new("+"), 2, 3)
+l2 = List.new(4, 5, 6)
+n = Interpreter.eval(l1, nil)
+print(n)