Robot Script Interpreter

--[[

    Author ayangd

    Thing: robot script interpret
    Description:
        Easily move robot with a line of string.

    Note:
        For ease use, just import this thing by:
            rim = require('<this module>').interpret
        then just do:
            rim('3u4d2(u4(lr))') or whatever movement you want to do
        (rim stands for RobotInterpretMovement)

    Usage:
        - 6 main functions:
            ( u, d, l, r, f, b ), each corresponding to
            ( up, down, left, right, forward, back)
            e.g robot forward twice then up:
                rim('ffu')
        - numbers:
            You can specify repetition of a function, just by specifying a number in front.
            e.g robot forward 4 times then up:
                rim('4fu')
        - subFunction:
            Wrap a snippet of instruction, and do numbers to easily repeat a function pattern.
            e.g robot (forward 4 times then up) 3 times:
                rim('3(4fu)')
        - xternalFunction:
            Call an external function parsed after the script.
            e.g robot forward 4 times and do something else:
                rim('4fx', doSomething)
            P.S it will pass no argument.

]]--
local robot = require('robot')

local interpreter = {}

-- Functions
local funcs = {}
function funcs.u()
    robot.up()
end

function funcs.d()
    robot.down()
end

function funcs.l()
    robot.turnLeft()
end

function funcs.r()
    robot.turnRight()
end

function funcs.f()
    robot.forward()
end

function funcs.b()
    robot.back()
end

-- Interpreter

function interpreter.interpret(s, xf)
    local repetition = 1
    local repeScan = ''
    local subScan = {}
    local scanMode = false
    local innerBrackets = 0
    for cp = 1, #s do
        local c = s:sub(cp, cp)
        if c == '(' then
            if scanMode == true then
                innerBrackets = innerBrackets + 1
                table.insert(subScan, c)
            else
                scanMode = true
            end
        elseif c == ')' then
            if innerBrackets ~= 0 then
                innerBrackets = innerBrackets - 1
                table.insert(subScan, c)
            else
                scanMode = false
                if repeScan ~= '' then
                    repetition = tonumber(repeScan)
                    repeScan = ''
                end
                local subScanRes = table.concat(subScan)
                for repe = 1, repetition do
                    interpreter.interpret(subScanRes, xf)
                end
                repetition = 1
                subScan = {}
            end
        elseif scanMode then
            table.insert(subScan, c)
        elseif tonumber(c) ~= nil then
            repeScan = repeScan .. c
        elseif c == 'x' then
            if repeScan ~= '' then
                repetition = tonumber(repeScan)
                repeScan = ''
            end
            for repe = 1, repetition do
                xf()
            end
        else
            local executed = false
            if repeScan ~= '' then
                repetition = tonumber(repeScan)
                repeScan = ''
            end
            for fn, f in pairs(funcs) do
                if c == fn then
                    executed = true
                    for repe = 1, repetition do
                        f()
                    end
                    repetition = 1
                    break
                end
            end
            if not executed then
                error(string.format('Interpretation failed at %d [unknown char %s].', cp, c), 2)
            end
        end
    end
    if scanMode then
        error('Expected ) at eol.', 2)
    end
    if repeScan ~= '' then
        error('Expected a function to repeat, found eol instead.', 2)
    end
end

return interpreter