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|
--- lam.eval
local eval = {}
local read = require "read"
local type = require "type"
local util = require "util"
local unpack = table.unpack or unpack
function eval.Env (inner, outer)
local mt = {
__type = "Environment",
__index = outer,
}
return setmetatable(inner, mt)
end
function eval.Proc (params, body, env)
local v = {
params = params,
body = body,
env = env,
}
local mt = {
__type = "Procedure",
__call =
function (self, args)
local inner = {}
local p, a = self.params, args
while p.cdr and a.cdr do
inner[p.car] = a.car
p, a = p.cdr, a.cdr
end
-- pp.pp(self.body)
return eval.eval(
self.body,
eval.Env(inner, self.env))
end,
}
return setmetatable(v, mt)
end
local global = {
begin =
function (args)
local a = args
while not type.isNull(a.cdr) do
a = a.cdr
end
return a.car
end,
["+"] =
function (args)
local acc = 0
local car, cdr = args.car, args.cdr
while cdr do
acc = acc + car
car, cdr = cdr.car, cdr.cdr
end
return acc
end,
["-"] =
function (args)
return args.car - args.cdr.car
end,
}
function eval.eval (x, env)
env = env or global
if type.isa(x, "Symbol") then
return env[x]
elseif not type.isList(x) then
return x
else
local op, args = x.car, x.cdr
if op == "quote" then
return args
elseif op == "define" then
env[args.car] = eval.eval(args.cdr.car, env)
return nil
elseif op == "lambda" then
return eval.Proc(
args.car,
type.Cons("begin", args.cdr),
env)
else -- procedure
local proc = eval.eval(op, env)
local params = {}
local a = args
while a.cdr do
table.insert(params, eval.eval(a.car, env))
a = a.cdr
end
return proc(type.List(params))
end
end
end
---
return eval
|
