From 9d42904e47c50c5ff2306da04993b2a32bc9cd16 Mon Sep 17 00:00:00 2001
From: Joel Martin <github@martintribe.org>
Date: Thu, 8 Jan 2015 23:25:40 -0600
Subject: Lua: all steps and self-hosting.

Also some misc docs/TODO updates.
---
 lua/step2_eval.lua | 75 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 75 insertions(+)
 create mode 100755 lua/step2_eval.lua

(limited to 'lua/step2_eval.lua')

diff --git a/lua/step2_eval.lua b/lua/step2_eval.lua
new file mode 100755
index 0000000..7487064
--- /dev/null
+++ b/lua/step2_eval.lua
@@ -0,0 +1,75 @@
+#!/usr/bin/env lua
+
+local table = require('table')
+
+local readline = require('readline')
+local utils = require('utils')
+local types = require('types')
+local reader = require('reader')
+local printer = require('printer')
+local List, Vector, HashMap = types.List, types.Vector, types.HashMap
+
+-- read
+function READ(str)
+    return reader.read_str(str)
+end
+
+-- eval
+function eval_ast(ast, env)
+    if types._symbol_Q(ast) then
+        if env[ast.val] == nil then
+            types.throw("'"..ast.val.."' not found")
+        end
+        return env[ast.val]
+    elseif types._list_Q(ast) then
+        return List:new(utils.map(function(x) return EVAL(x,env) end,ast))
+    elseif types._vector_Q(ast) then
+        return Vector:new(utils.map(function(x) return EVAL(x,env) end,ast))
+    elseif types._hash_map_Q(ast) then
+        local new_hm = {}
+        for k,v in pairs(ast) do
+            new_hm[EVAL(k, env)] = EVAL(v, env)
+        end
+        return HashMap:new(new_hm)
+    else
+        return ast
+    end
+end
+
+function EVAL(ast, env)
+    --print("EVAL: "..printer._pr_str(ast,true))
+    if not types._list_Q(ast) then return eval_ast(ast, env) end
+    local args = eval_ast(ast, env)
+    local f = table.remove(args, 1)
+    return f(unpack(args))
+end
+
+-- print
+function PRINT(exp)
+    return printer._pr_str(exp, true)
+end
+
+-- repl
+local repl_env = {['+'] = function(a,b) return a+b end,
+                  ['-'] = function(a,b) return a-b end,
+                  ['*'] = function(a,b) return a*b end,
+                  ['/'] = function(a,b) return math.floor(a/b) end}
+function rep(str)
+    return PRINT(EVAL(READ(str),repl_env))
+end
+
+while true do
+    line = readline.readline("user> ")
+    if not line then break end
+    xpcall(function()
+        print(rep(line))
+    end, function(exc)
+        if exc then
+            if types._malexception_Q(exc) then
+                exc = printer._pr_str(exc.val, true)
+            end
+            print("Error: " .. exc)
+            print(debug.traceback())
+        end
+    end)
+end
-- 
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