Initial data commit

Task/Queue-Definition/R/queue-definition-2.r

@@ -0,0 +1,39 @@
+# The usual Scheme way : build a function that takes commands as parameters (it's like message passing oriented programming)
+queue <- function() {
+    v <- list()
+    f <- function(cmd, val=NULL) {
+        if(cmd == "push") {
+            v <<- c(v, val)
+            invisible()
+        } else if(cmd == "pop") {
+            if(length(v) == 0) {
+                stop("empty queue")
+            } else {
+                x <- v[[1]]
+                v[[1]] <<- NULL
+                x
+            }
+        } else if(cmd == "length") {
+            length(v)
+        } else if(cmd == "empty") {
+            length(v) == 0
+        } else {
+            stop("unknown command")
+        }
+    }
+    f
+}
+
+# Create two queues
+a <- queue()
+b <- queue()
+a("push", 1)
+a("push", 2)
+b("push", 3)
+a("push", 4)
+b("push", 5)
+
+a("pop")
+# [1] 1
+b("pop")
+# [1] 3