Add InputStream type.

InputStream.tl

@@ -0,0 +1,48 @@
+local type InputStream = record
+	str: string
+	offset: number
+	refill: function(): string
+end
+
+local istream_mt = {__index = InputStream}
+
+function InputStream:_manageBuffer()
+	if self.offset > #self.str then
+		self.str = self.refill()
+		self.offset = 1
+	end
+end
+
+
+
+-- constructors
+function InputStream:new(): InputStream
+	return setmetatable(
+		{
+			string = "",
+			offset = 1
+		} as InputStream,
+		istream_mt)
+end
+
+-- setters/getters
+function InputStream:setRefill(func: function(): string)
+	self.refill = func
+end
+
+-- 
+function InputStream:readCurrentCharacter(): string
+	self:_manageBuffer()
+	return self.str:sub(self.offset, 1)
+end
+
+function InputStream:advanceOffset(): string
+	self.offset = self.offset + 1
+	self:_manageBuffer()
+	return self.str:sub(self.offset, 1)
+end
+
+return InputStream
+
+
+