Befunge Interpreter

function run(tbl, name, debug, limitx, limity)
    w, h = term.getSize()
    limitx, limity = limitx or w, limity or h

    for _x=0, limitx do
        if not tbl[_x] then tbl[_x] = {} end
        for _y=0, limity do
            if not tbl[_x][_y] then
                tbl[_x][_y] = " "
            end
        end
    end

    local x, y = 0, 0
    local vx, vy = 1, 0
    local stringmode = false
    local stack = {}
    local bExit = false

    local function push(n)
        table.insert(stack, n)
    end
    local function pop()
        if stack[#stack] then
            return table.remove(stack, #stack)
        else
            error((name or "befunge")..": ("..x..", "..y..") Stack is empty!", 0)
        end
    end

    local lastchar = " "
    local lastx, lasty = 1, 1
    local first = true
    local function draw()
        if debug then

            for _x,v in pairs(tbl) do
                for _y,char in pairs(v) do
                    if _x == x and _y == y then
                        term.setBackgroundColor(colors.yellow)
                        lastchar = char
                        lastx, lasty = _x, _y
                    else
                        term.setBackgroundColor(colors.black)
                    end
                    if ((char ~= " ") and first) or (_x==x and _y==y)then
                        term.setCursorPos(_x+1, _y+1)
                        write(char)
                    end
                end
            end

            sleep(0.1)
            term.setBackgroundColor(colors.black)
            term.setCursorPos(lastx+1, lasty+1)
            term.write(lastchar)

            first = false
        end
    end

    local cmds = {
        -- Befunge-93 Instruction List from http://en.wikipedia.org/wiki/Befunge
        ["+"] = function() a = pop() b = pop() push(a+b) end, -- Addition: Pop a and b, then push a+b
        ["-"] = function() a = pop() b = pop() push(a-b) end, -- Subtraction: Pop a and b, then push b-a
        ["*"] = function() a = pop() b = pop() push(a*b) end, -- Multiplication: Pop a and b, then push a*b
        ["/"] = function() a = pop() b = pop() push(a/b) end, -- Integer division: Pop a and b, then push b/a, rounded down. If a is zero, ask the user what result they want
        ["%"] = function() a = pop() b = pop() push(a%b) end, -- Modulo: Pop a and b, then push the remainder of the integer division of b/a. If a is zero, ask the user what result they want
        ["!"] = function() a = pop() if a == 0 then push(1) else push(0) end end, -- Logical NOT: Pop a value. If the value is zero, push 1; otherwise, push zero
        ["`"] = function() a = pop() b = pop() if b>a then push(1) else push(0) end end, -- Greater than: Pop a and b, then push 1 if b>a, otherwise zero
        [">"] = function() vx, vy = 1, 0 end, -- Start moving right
        ["<"] = function() vx, vy = -1, 0 end, -- Start moving left
        ["^"] = function() vx, vy = 0, -1 end, -- Start moving up
        ["v"] = function() vx, vy = 0, 1 end, -- Start moving down
        ["?"] = function() -- Start moving in a random cardinal direction
            local dir = math.random(1, 4)
            if dir == 1 then vx, vy = 1, 0
            elseif dir == 2 then vx, vy = -1, 0
            elseif dir == 3 then vx, vy = 0, -1
            elseif dir == 4 then vx, vy = 0, 1
            end
        end,
        ["_"] = function() a = pop() -- Pop a value; move right if value=0, left otherwise
            if a == 0 then
                vx, vy = 1, 0
            else
                vx, vy = -1, 0
            end
        end,
        ["|"] = function() a = pop() -- Pop a value; move down if value=0, up otherwise
            if a == 0 then
                vx, vy = 0, 1
            else
                vx, vy = 0, -1
            end
        end,
        ['"'] = function() stringmode = not stringmode end, -- Start string mode: push each character's ASCII value all the way up to the next "
        [":"] = function() push(stack[#stack]) end, -- Duplicate value on top of the stack
       ["\\"] = function() a = pop() b = pop() push(a) push(b) end, -- Swap two values on top of the stack
        ["$"] = function() pop() end, -- Pop value from the stack
        ["."] = function()  -- Pop value and output as an integer
            if debug then term.setCursorPos(1, h) end
            write(pop())
            if debug then sleep(0.1) end
        end,
        [","] = function() -- Pop value and output as ASCII character
            if debug then term.setCursorPos(1, h) end
            write(string.char(pop()))
            if debug then sleep(0.1) end
        end,
        ["#"] = function() x, y = x+vx, y+vy end, -- Trampoline: Skip next cell
        ["p"] = function() -- A "put" call (a way to store a value for later use). Pop y, x and v, then change the character at the position (x,y) in the program to the character with ASCII value v
            local _y, _x, v = pop(), pop(), pop()
            tbl[_x][_y] = string.char(v)
            first = true
        end,
        ["g"] = function()
            local _y, _x = pop(), pop()
            push(string.byte(tbl[_x][_y]))
        end, -- A "get" call (a way to retrieve data in storage). Pop y and x, then push ASCII value of the character at that position in the program
        ["&"] = function()  -- Ask user for a number and push it
            if debug then term.setCursorPos(1, h) end
            num = read()
            push(tonumber(num) or 0)
            term.clear()
            first = true
        end,
        ["~"] = function() -- Ask user for a character and push its ASCII value
            if debug then term.setCursorPos(1, h) end
            char = read()
            push(string.byte(string.sub(char, 1, 1)))
            term.clear()
            first = true
        end,
        ["@"] = function() bExit = true end, -- End program
        [" "] = function() end, -- No-op. Does nothing

        ["s"] = function() sleep(0) end -- Sleep, add to avoid "Too Long without Yielding" error
    }

    term.clear()
    while not bExit do
        draw()
        --if not tbl[x] or not tbl[x][y]then
        --  error((name or "befunge")..": ("..x..", "..y..") Instruction does not exist!", 0)
        --end
        local cmd
        if tbl[x] then
            cmd = tbl[x][y] or " "
        else
            cmd = " "
        end
        if stringmode and cmd ~= '"' then -- within ""
            push(string.byte(cmd))
        elseif string.match(cmd, "%d") then -- a number
            push(tonumber(cmd))
        else -- a command
            if cmds[cmd] then
                cmds[cmd]()
            else
                error((name or "befunge")..": ("..x..", "..y..") Unknown instruction!", 0)
            end
        end

        x, y = (x+vx)%80, (y+vy)%20
    end
    print("")
end

function load(path)
    local file = io.open(path, "r")
    local tbl = {}
    local y = 0

    for line in file:lines() do
        for x=1, line:len() do
            if not tbl[x-1] then tbl[x-1] = {} end
            tbl[x-1][y] = string.sub(line, x, x)
        end
        y = y + 1
    end

    return tbl
end

tArgs = {...}
run(load(tArgs[1]), tArgs[1], tArgs[2])