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