Initial data commit

Task/Queue-Definition/R/queue-definition-3.r

@@ -0,0 +1,30 @@
+library(proto)
+
+fifo <- proto(expr = {
+   l <- list()
+   empty <- function(.) length(.$l) == 0
+   push <- function(., x)
+   {
+      .$l <- c(.$l, list(x))
+      print(.$l)
+      invisible()
+   }
+   pop <- function(.)
+   {
+      if(.$empty()) stop("can't pop from an empty list")
+      .$l[[1]] <- NULL
+      print(.$l)
+      invisible()
+   }
+})
+
+#The following code provides output that is the same as the previous example.
+fifo$empty()
+fifo$push(3)
+fifo$push("abc")
+fifo$push(matrix(1:6, nrow=2))
+fifo$empty()
+fifo$pop()
+fifo$pop()
+fifo$pop()
+fifo$pop()