lua-haskell-interpreter

A simple interactive lua interpreter implemented in Haskell

Supported Features

• Primitive types
• Variables
• Tables
• Control Structures
• Functions
• Metatables & Metamethods

Limitations

• Input in interactive shell does not support proper cursor movement codes. It is recommended to directly copy complete statement into the shell.
• Only single line statement input is supported. Use do S;S1 end to sequence multiple statements together.
• Float number literals / scientific notations are not supported.
• Combination of features could not work, e.g. non-tail break statement in sequenced statements inside loops.
• Lua implicit table key deduction for array-like syntax is not implemented.

Run interpretor

stack build
stack exec main

Or in GHCi

> :load Main
*Main> main

Lua> print("Hello World")
Lua> quit

Basic operations

a = {}
a[20] = "great"
print(a[20])
k = 20
print(a[k])

do t = {[1] = 99, ["x"]="abc", [#"key"]=true}; print (t) end

Sequence and Control Structure

do a=20;b=40;op="+" end

if a > b then print(a) else print(b) end

if op == "+" then return a + b elseif op == "-" then return a - b else return -1 end

for i=10,1,-3 do print(i) end

do v=0; for i=1,10 do v = v+i end; print(v) end

v = 1

while v do do v=v*2; if v > 5 then break end end end

Functions

function tdouble(v) return 2*v end

print(tdouble(13))

function tmulti(a,b) return a*b end

print(tmulti(13,14))

function tcircum(r) do pi=314;return 2*pi*r/100 end end

print(tcircum(100))

OOP Style

Square inherits methods from Shape while overridding the name method

Shape = {}
function Shape:family() return "Shape" end
function Shape:name() return "Shape" end
function Shape:new() do o={};o["__metatable"]=self; return o end end

Square = Shape:new()
function Square:area() return self.x * self.x end
function Square:name() return "Square" end

function Square:new() do o={};o["__metatable"]=self; return o end end
o = Square:new()
o["x"] = 16
print(o:area())
print(o:name())
print(o:family())

MetaMethod with operator + and -

Point = {}
function Point:square() return self.x^2 + self.y^2 end
function Point:add(p) do o={};o["__metatable"]=self["__metatable"];o["x"]=self.x+p.x;o["y"]=self.y+p.y;return o end end
function Point:sub(p) do o={};o["__metatable"]=self["__metatable"];o["x"]=self.x-p.x;o["y"]=self.y-p.y;return o end end
Point["__add"] = Point.add
Point["__sub"] = Point.sub
function Point:new(x,y) do o={};o["__metatable"]=self;o["x"]=x;o["y"]=y;return o end end

do a = Point:new(3,4); b = Point:new(1,1) end
c = a + b
c.x
c:square()
c = a - b
c.x

Citations & References

UIUC CS421 MP4 & MP5 github

• Code structure
• Parser usage
• Unit tests

Programming in Lua

• Lua features and code examples

Lua-Interpretor github

• Lua binary operators
• Unit tests