Kalkulator

-- This program is public domain. Do whatever you want with it.

local expr

local spacechars = " \t\n\r"

local function skipspaces()
 while spacechars:find(expr:sub(1, 1),1,true) ~= nil and expr:len() > 0 do
  expr = expr:sub(2)
 end
end

local function acceptch(ch)
 skipspaces()
 if expr:sub(1,1) == ch then
  expr = expr:sub(2)
  return true
 else
  return false
 end
end

local function acceptnum()
 skipspaces()
 -- I'm sure there's a better way
 for len = expr:len(), 1, -1 do
  local success, n = pcall(tonumber, expr:sub(1, len))
  if success and n ~= nil then
   expr = expr:sub(len + 1)
   return n
  end
 end
 return nil
end

local alpha = "_abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
local alnum = alpha .. "0123456789"

local function acceptident()
 local n = 0
 skipspaces()
 if alpha:find(expr:sub(1, 1),1,true) == nil then return nil end
 while alnum:find(expr:sub(n+1, n+1),1,true) ~= nil and expr:len() > n do
  n = n + 1
 end
 local ident = expr:sub(1, n)
 expr = expr:sub(n+1)
 return ident
end

local function parse_error(s)
 error(s and ("parse error: " .. s) or "parse error")
end

local expression_root

local math_functions = {
abs = math.abs,
acos = math.acos,
asin = math.asin,
atan = math.atan,
atan2 = math.atan2,
ceil = math.ceil,
floor = math.floor,
cos = math.cos,
sin = math.sin,
tan = math.tan,
cosh = math.cosh,
sinh = math.sinh,
tanh = math.tanh,
-- math.deg, math.rad
exp = math.exp,
ln = math.log,
log = math.log10,
pow = math.pow,
min = math.min,
max = math.max,
sqrt = math.sqrt,
random = math.random
}

local math_constants = {
pi = math.pi,
e = math.exp(1),
inf = math.huge,
nan = math.huge - math.huge
}

local function call_function(id, arglist)
 if math_functions[id] == nil then
  error("no such function: " .. id)
 end
 return math_functions[id](unpack(arglist))
end

local function get_constant(id)
 return math_constants[id] or error("no such constant: "..id)
end

local function num_or_brackets()
 if acceptch("(") then
  local n = expression_root()
  if not acceptch(")") then parse_error("non-matching parentheses") end
  return n
 elseif acceptch("-") then
  return -expression_root()
 else
  local id = acceptident()
  if id ~= nil then
   if not acceptch("(") then
    return get_constant(id)
   elseif acceptch(")") then
    return call_function(id, {})
   else
    local arglist = {}
    local done = false
    while not done do
     table.insert(arglist, expression_root())
     if acceptch(")") then
      done = true
     elseif not acceptch(",") then
      parse_error("expected , or )")
     end
    end
    return call_function(id, arglist)
   end
  else
   local n = acceptnum()
   if n == nil then parse_error("expected number or bracketed expression") end
   return n
  end
 end
end

local function division()
 local n1 = num_or_brackets()
 while acceptch("/") do
  n1 = n1 / num_or_brackets()
 end
 return n1
end

local function multiplication()
 local n1 = division()
 while acceptch("*") do
  n1 = n1 * division()
 end
 return n1
end
local function subtraction()
 local n1 = multiplication()
 while acceptch("-") do
  n1 = n1 - multiplication()
 end
 return n1
end
local function addition()
 local n1 = subtraction()
 while acceptch("+") do
  n1 = n1 + subtraction()
 end
 return n1
end
expression_root = addition

local function parse(e)
 expr = e
 local success, result = pcall(expression_root)
 if success and expr ~= "" then
  print("Garbage after expression?")
 end
 if success then
  print("Answer: " .. tostring(result))
 else
  print(result)
  print("Near: " .. (expr == "" and "end of expression" or expr))
 end
end

local function mainloop()
 local quitting = false
 print("")
 print("Kalkulator by Hogohin v1.0")
 print("")
 print("Wpisuj rownania i zatwierdz enter")
 print("Wpisz 'wyjdz' aby wyjsc")
 print("")
 while not quitting do
  local line = io.read()
  if line == "wyjdz" then
   quitting = true
  else
   parse(line)
   print("")
  end
 end
end

mainloop()