diff --git a/lama-spec.pdf b/lama-spec.pdf
index 46874c8e7..98ea3fa3e 100644
Binary files a/lama-spec.pdf and b/lama-spec.pdf differ
diff --git a/runtime/runtime.c b/runtime/runtime.c
index 7dc479224..45fde2475 100644
--- a/runtime/runtime.c
+++ b/runtime/runtime.c
@@ -1512,7 +1512,7 @@ extern void __gc_root_scan_stack ();
 /* ======================================== */
 
 //static size_t SPACE_SIZE = 16;
-static size_t SPACE_SIZE = 64 * 1024 * 1024;
+static size_t SPACE_SIZE = 256 * 1024 * 1024;
 // static size_t SPACE_SIZE = 128;
 // static size_t SPACE_SIZE = 1024 * 1024;
 
diff --git a/spec/06.standard_library.tex b/spec/06.standard_library.tex
index 6d0f51ef2..3bf2dd7a5 100644
--- a/spec/06.standard_library.tex
+++ b/spec/06.standard_library.tex
@@ -94,6 +94,45 @@ program start time.}
 
 \descr{\lstinline|fun time ()|}{Returns the elapsed time from program start in microseconds.}
 
+\section{Unit \texttt{Data}}
+\label{sec:data}
+
+Generic data manupulation.
+
+\descr{\lstinline|infix =?= at < (x, y)|}{A generic comparison operator similar to \lstinline|compare|, but capable of handling cyclic/shared data structures.}
+\descr{\lstinline|infix === at == (x, y)|}{A generic equality operator capable of handling cyclic/shared data structures.}
+
+\section{Unit \texttt{Random}}
+\label{sec:random}
+
+Random data structures generation functions.
+
+\descr{\lstinline|fun randomInt ()|}{Generates a random representable integer value.}
+
+\descr{\lstinline|fun randomString (len)|}{Generates a random string of printable ASCII characters of given length.}
+
+\descr{\lstinline|fun randomArray (f, n)|}{Generates a random array of \emph{deep} size \lstinline|n|. The length of the array is chosen randomly, and \lstinline|f| is intended to be an element-generating function which takes the size of the element as an argument.}
+
+\descr{\lstinline|fun split (n, k)|}{Splits a non-negative integer \lstinline|n| in \lstinline|k| random summands. Returns an array if length \lstinline|k|. \lstinline|k| has to be non-negative.}
+
+\newsavebox\strubox
+
+\begin{lrbox}{\strubox}
+\begin{lstlisting}
+    structure (100,
+               [[2, fun ([x, y]) {Add (x, y)}],
+                [2, fun ([x, y]) {Sub (x, y)}]],
+               fun () {Const (randomInt ())}
+              )    
+\end{lstlisting}  
+\end{lrbox}
+
+\descr{\lstinline|fun structure (n, nodeSpec, leaf)|}{Generates a random tree-shaped data structure of size \lstinline|n|. \lstinline|nodeSpec| is an array of pairs \lstinline|[$k$, $f_k$]|, where $k$ is a non-negative integer and $f_k$ is a function which takes an array of length $k$ as its argument. Each pair describes a generator of a certain kind of interior node with degree $k$. \lstinline|leaf| is a zero-argument function which generates the leaves of the tree. For example, the following code
+
+\usebox\strubox
+
+can be used to generate a random arithmetic expression of size 100.}
+
 \section{Unit \texttt{Array}}
 \label{sec:array}
 
@@ -308,6 +347,27 @@ fresh list if images in the same order.}
 \descr{\lstinline|fun filter (f, l)|}{Removes all values, not satisfying the predicate "\lstinline|f|", from the list "\lstinline|l|". The function
 "\lstinline|f|" should return integers, treated as booleans.}
 
+\section{Unit \texttt{Buffer}}
+\label{sec:std:buffer}
+
+Mutable buffers.
+
+\descr{\lstinline|fun emptyBuffer ()|}{Creates an empty buffer.}
+
+\descr{\lstinline|fun singletonBuffer (x)|}{Creates a buffer from a single element.}
+
+\descr{\lstinline|fun listBuffer (x)|}{Creates a buffer from a list.}
+
+\descr{\lstinline|fun getBuffer (buf)|}{Gets the contents of a buffer as a list.}
+
+\descr{\lstinline|fun addBuffer (buf, x)|}{Adds an element \lstinline|x| to the end of buffer \lstinline|buf| and returns the updated buffer. The buffer \lstinline|buf| can be updated in-place.}
+
+\descr{\lstinline|fun concatBuffer (buf, x)|}{Adds buffer \lstinline|x| to the end of buffer \lstinline|buf| and returns the updated buffer. The buffer \lstinline|buf| can be updated in-place.}
+
+\descr{\lstinline|infixl <+> before + (b1, b2)|}{Infix synonym for \lstinline|concatBuffer|.}
+
+\descr{\lstinline|infix <+ at <+> (b, x)|}{Infix synonym for \lstinline|addBuffer|.}
+
 \section{Unit \texttt{Matcher}}
 
 The unit provides some primitives for matching strings against regular patterns. Matchers are immutable structures which store
diff --git a/src/version.ml b/src/version.ml
index 86effb8bc..a234ecfdc 100644
--- a/src/version.ml
+++ b/src/version.ml
@@ -1 +1 @@
-let version = "Version 1.00, 6f9d0850c, Fri Aug 7 21:40:51 2020 +0300"
+let version = "Version 1.00, 94e4b1626, Mon Aug 10 20:55:10 2020 +0300"
diff --git a/stdlib/Buffer.lama b/stdlib/Buffer.lama
new file mode 100644
index 000000000..4e19e9c93
--- /dev/null
+++ b/stdlib/Buffer.lama
@@ -0,0 +1,66 @@
+-- Buffer.
+-- (C) Dmitry Boulytchev, JetBrains Research, St. Petersburg State University, 2020
+--
+-- This unit provides a simple add-to-the-end buffer implemetation.
+
+import List;
+
+-- Creates an empty buffer
+public fun emptyBuffer () {
+  {}
+}
+
+-- Creates a buffer with one element x
+public fun singletonBuffer (x) {
+  local y = singleton (x);
+
+  [y, y]
+}  
+
+-- Creates a buffer from a list x
+public fun listBuffer (x) {
+  foldl (addBuffer, emptyBuffer (), x)
+}
+
+-- Adds x to the end of buffer buf
+public fun addBuffer (buf, x) {
+  case buf of
+    {} -> local y = singleton (x);
+          [y, y]          
+  | [head, last] ->
+          last[1] := singleton (x);
+          [head, last[1]]
+  esac
+}
+
+-- Adds the contents of buffer x to the end of buffer buf
+public fun concatBuffer (buf, x) {
+  case buf of
+    {}           -> x
+  | [head, last] ->
+       case x of
+         {}     -> buf
+       | [h, l] ->
+           last[1] := h;
+           [head, l]
+       esac
+  esac
+}
+
+-- Infix synonym for concatBuffer
+public infixl <+> before + (b1, b2) {
+  concatBuffer (b1, b2)
+}
+
+-- Infix synonym for addBuffer
+public infix <+ at <+> (b, x) {
+  addBuffer (b, x)
+}
+
+-- Gets the contents of the buffer buf (as a list)
+public fun getBuffer (buf) {
+  case buf of
+    {}        -> {}
+  | [head, _] -> head
+  esac
+}
diff --git a/stdlib/List.lama b/stdlib/List.lama
index c2dc5143f..4ed5f856e 100644
--- a/stdlib/List.lama
+++ b/stdlib/List.lama
@@ -79,12 +79,20 @@ public fun flatten (l) {
 
   fun append (x) {
     local new = x : {};
-
+    
     curr [0][1] := new;
     curr [0] := new    
   }
+
+  fun traverse (l) {
+    case l of
+      _ : _ -> iter (traverse, l)
+    | {}    -> skip
+    | _     -> append (l)
+    esac
+  }
   
-  iter (fun (x) {iter (append, x)}, l);
+  traverse (l);
   
   res [1]
 }
diff --git a/stdlib/Makefile b/stdlib/Makefile
index 69403a61e..e6ce887f0 100644
--- a/stdlib/Makefile
+++ b/stdlib/Makefile
@@ -16,6 +16,8 @@ Array.o: List.o
 
 Ostap.o: List.o Collection.o Ref.o Fun.o Matcher.o
 
+Buffer.o: List.o
+
 Expr.o: Ostap.o
 
 %.o: %.lama
diff --git a/stdlib/Random.lama b/stdlib/Random.lama
index a6d325fea..257f4683c 100644
--- a/stdlib/Random.lama
+++ b/stdlib/Random.lama
@@ -28,13 +28,12 @@ public fun randomString (len) {
 -- Generates a random array of (deep) size n. f is element-generation
 -- function which takes the size of the element
 public fun randomArray (f, n) {
-  mapArray (f, split (n))  
+  mapArray (f, split (n, random (n + 1)))  
 }
 
--- Splits a number in a random sequence of summands
-public fun split (n) {
-  local k = random (n) + 1,
-        a = makeArray (k),
+-- Splits a number n in a random sequence of k summands
+public fun split (n, k) {
+  local a = makeArray (k),
         m = n;
 
   for local i = 0;, i < k, i := i + 1
@@ -49,3 +48,22 @@ public fun split (n) {
 
   a
 }
+
+-- Generates a (recursive) data structure of size n. nodeSpec is an array of pairs [n, fn] where
+-- fn gets an array of values of length n and generates some node; leaf is a fucntion without
+-- arguments which create a leaf.
+public fun structure (n, nodeSpec, leaf) {
+  local k = nodeSpec.length;
+
+  fun rec (n) {
+    if n <= 1
+    then leaf ()
+    else
+      local ns = nodeSpec [random (k)];
+      
+      ns [1] (mapArray (rec, split (n, ns [0])))
+    fi
+  }
+
+  rec (n)
+}
\ No newline at end of file
diff --git a/stdlib/regression/test30.lama b/stdlib/regression/test30.lama
index c3807915d..35c059e60 100644
--- a/stdlib/regression/test30.lama
+++ b/stdlib/regression/test30.lama
@@ -24,7 +24,7 @@ fun genCyclicArrays (n, eq, cross) {
         x -> [x, clone (x)]
       esac           
     else
-      local a     = split (n),
+      local a     = split (n, random (n+1)),
             b     = mapArray (id, a),
             index = initArray (random (a.length + 1), fun (_) {random (a.length)});