tasks a-s

Task/Queue-Definition/R/queue-definition-1.r

@@ -0,0 +1,48 @@
+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()
+}
+l <- list()
+empty()
+# [1] TRUE
+push(3)
+# [[1]]
+# [1] 3
+push("abc")
+# [[1]]
+# [1] 3
+# [[2]]
+# [1] "abc"
+push(matrix(1:6, nrow=2))
+# [[1]]
+# [1] 3
+# [[2]]
+# [1] "abc"
+# [[3]]
+#      [,1] [,2] [,3]
+# [1,]    1    3    5
+# [2,]    2    4    6
+empty()
+# [1] FALSE
+pop()
+# [[1]]
+# [1] 3
+# [[2]]
+# [1] "abc"
+pop()
+# [[1]]
+# [1] 3
+pop()
+# list()
+pop()
+# Error in pop() : can't pop from an empty list

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

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()