local type InputStream = record str: string offset: number refill: function(): string new: function(InputStream, function(): string): InputStream __setRefill: function(InputStream, function(): string) readCurrentCharacter: function(): string advanceOffset: function(): string end local istream_mt = {__index = InputStream} function InputStream:_manageBuffer() if not self.str then self.str = self.refill() self.offset = 1 end if self.offset > #self.str then self.str = self.refill() self.offset = 1 end end local function initial_stream(): string return "DUMMY" end -- constructors function InputStream:new(refill: function(): string): InputStream refill = refill or initial_stream local istream = setmetatable( { string = "", offset = 1, } as InputStream, istream_mt) istream:__setRefill(refill) return istream end -- setters/getters function InputStream:__setRefill(func: function(): string) self.refill = func self:_manageBuffer() end -- function InputStream:curr(): string return self.str:sub(self.offset, self.offset) end function InputStream:next(): string self:_manageBuffer() local current_char = self.str:sub(self.offset, self.offset) self.offset = self.offset + 1 return current_char end return InputStream