
dtonhofer
Functional Programming in Java, Second Edition: All the code for Chapter 8, "Using Tail-Call Optimization", in one class
All the code for Chapter 8, Using Tail-Call Optimization, in one class. But without the part where we later need to “fix the arithmetic overflow”, an ancillary problem that is solely due to the fact that the example recursive function we use is the factorial. Here we use a simple recursive sum instead.
package chapter8.tailcalls;
import org.junit.jupiter.api.Test;
import java.util.function.Function;
import java.util.stream.Stream;
public class Chapter8_TailCallOptimization {
private final static int limit = 70000;
// ---
// The "very slick stack simulator" (VSSS) for optimizable (not necessarily recursive) tail calls
// This is the code "recur/fpij/TailCall.java" on p.142
// with a fix: the .get() on the Stream has been replaced by .orElseThrow()
// If we only use get(), the linter tells us: "Optional.get() without "isPresent()" check".
// ---
@FunctionalInterface
public interface TailCall<T> {
TailCall<T> apply();
default boolean isComplete() {
return false;
}
default T result() {
throw new Error("not implemented");
}
default T invoke() {
return Stream.iterate(this, TailCall::apply)
.filter(TailCall::isComplete)
.findFirst()
.orElseThrow()
.result();
}
}
// "recur/fpij/TailCalls.java" on p.143
public static class TailCalls {
// call() simply exists so that usage has a symmetric look
// (...but I'm not sure this improves understanding)
public static <T> TailCall<T> call(final TailCall<T> nextCall) {
return nextCall;
}
public static <T> TailCall<T> done(final T value) {
return new TailCall<T>() {
@Override
public boolean isComplete() {
return true;
}
@Override
public T result() {
return value;
}
@Override
public TailCall<T> apply() {
throw new Error("not implemented");
}
};
}
}
// ---
// Summing using a recursive call that is not a tail call (avoid if possible, though
// it is not always possible)
// Replaces "recur/fpij/Factorial.java" on page 140.
// ---
private static class SumRecursivelyNaively {
public static long sum(final int number) {
return (number == 1) ? 1 : (number + sum(number - 1));
}
}
// ---
// Summing using a recursive call that is a proper tail call.
// This approach uses an accumulator while going "down/into" the recursion.
// On the way "back up/outo of" the recursion there are only "returns".
// This can be optimized so that only 1 stack frame is used. However, the Java compiler
// (and/or the JVM?) does not do that fully (maybe because it needs to keep track of
// stack frames for debugging?), so we still get stack overflow after some time.
// ---
private static class SumRecursivelyUsingTailCalls {
public static long sum(final int number) {
return sum_inner(1, number);
}
private static long sum_inner(final long accumulator, final int number) {
if (number == 1) {
return accumulator;
} else {
return sum_inner(accumulator + number, number - 1);
}
}
}
// ---
// An application of VSSS - the very sly stack simulator
// Replaces "recur/fpij/Factorial.java" on p.141
// ---
private static class SumRecursivelyWithVSSS {
public static long sum(final int number) {
return sum_inner(1, number).invoke();
}
// Note that this method is *never* called recursively!
public static TailCall<Long> sum_inner(final long accumulator, final int number) {
if (number == 1) {
// Return the "TailCalls" instance that ends the stream
return TailCalls.done(accumulator);
} else {
// "call()" does nothing, and we could just return the closure directly, but it looks nice
return TailCalls.call(
// When called by Stream.iterate(), this closure is supposed to generate&return the
// "next TailCall instance" of the stream
() -> sum_inner(accumulator + number, number - 1)
);
}
}
}
// === TESTING SUPPORT BEGINS ===
private static boolean callSum(final boolean skip, final String name, int n, Function<Integer, Long> sum) {
boolean skipNextTime = skip;
if (!skip) {
try {
long res = sum.apply(n);
// Properly, this test should be in the caller
if (n == limit - 1) {
System.out.println("Reached the end: " + name + "(" + n + ") = " + res);
}
} catch (StackOverflowError err) {
System.out.println("Stack overflow for " + name + "(" + n + ")");
skipNextTime = true;
}
}
return skipNextTime;
}
// Running the three approaches at summing recursively till stack overflow occurs!
// Works best if one reduces the maximum stack size of the JVM,
// options "-Xss1m" or "-XX:ThreadStackSize=1024" (the latter in KiB)
// See https://docs.oracle.com/en/java/javase/17/docs/specs/man/java.html#advanced-runtime-options-for-java
//
// Example output:
//
// Stack overflow for SumRecursivelyNaively.sum(38919)
// Stack overflow for SumRecursivelyUsingTailCalls.sum(58375)
// Reached the end: SumRecursivelyWithVSSS.sum(69999) = 2449965000
@Test
public void runThem() {
boolean skipNaiveVersion = false;
boolean skipTailCallVersion = false;
boolean skipVsssVersion = false;
for (int n = 1; n < limit && !(skipTailCallVersion && skipNaiveVersion && skipVsssVersion); n += 1) {
skipNaiveVersion = callSum(skipNaiveVersion, "SumRecursivelyNaively.sum", n, SumRecursivelyNaively::sum);
skipTailCallVersion = callSum(skipTailCallVersion, "SumRecursivelyUsingTailCalls.sum", n, SumRecursivelyUsingTailCalls::sum);
skipVsssVersion = callSum(skipVsssVersion, "SumRecursivelyWithVSSS.sum", n, SumRecursivelyWithVSSS::sum);
}
}
}
Popular Pragmatic Bookshelf topics

Following the steps described in Chapter 6 of the book, I’m stuck with running the migration as described on page 84:
bundle exec sequel...
New

Title: Design and Build Great Web APIs - typo “https://company-atk.herokuapp.com/2258ie4t68jv” (page 19, third bullet in URL list)
Typo:...
New

Hi everyone!
There is an error on the page 71 in the book “Programming machine learning from coding to depp learning” P. Perrotta. You c...
New

I am working on the “Your Turn” for chapter one and building out the restart button talked about on page 27. It recommends looking into ...
New

I ran this command after installing the sample application:
$ cards add do something --owner Brian
And got a file not found error:
Fil...
New

I found an issue in Chapter 7 regarding android:backgroundTint vs app:backgroundTint.
How to replicate:
load chapter-7 from zipfile i...
New

Is the book’s epub format available to read on Google Play Books?
New

On page 78 the following code appears:
<%= link_to ‘Destroy’, product,
class: ‘hover:underline’,
method: :delete,
data: { confirm...
New

Hi all,
currently I wonder how the Tailwind colours work (or don’t work).
For example, in app/views/layouts/application.html.erb I have...
New

Getting an error when installing the dependencies at the start of this chapter:
could not compile dependency :exla, "mix compile" failed...
New
Other popular topics

Bought the Moonlander mechanical keyboard. Cherry Brown MX switches. Arms and wrists have been hurting enough that it’s time I did someth...
New

If you are experiencing Rails console using 100% CPU on your dev machine, then updating your development and test gems might fix the issu...
New

Create efficient, elegant software tests in pytest, Python's most powerful testing framework.
Brian Okken @brianokken
Edited by Kat...
New

This is going to be a long an frequently posted thread.
While talking to a friend of mine who has taken data structure and algorithm cou...
New

Author Spotlight
Jamis Buck
@jamis
This month, we have the pleasure of spotlighting author Jamis Buck, who has written Mazes for Prog...
New

I am trying to crate a game for the Nintendo switch, I wanted to use Java as I am comfortable with that programming language. Can you use...
New

Programming Ruby is the most complete book on Ruby, covering both the language itself and the standard library as well as commonly used t...
New

I have always used antique keyboards like Cherry MX 1800 or Cherry MX 8100 and almost always have modified the switches in some way, like...
New

I’m able to do the “artistic” part of game-development; character designing/modeling, music, environment modeling, etc.
However, I don’t...
New

Node.js v22.14.0 has been released.
Link: Release 2025-02-11, Version 22.14.0 'Jod' (LTS), @aduh95 · nodejs/node · GitHub
New
Categories:
Sub Categories:
Popular Portals
- /elixir
- /rust
- /ruby
- /wasm
- /erlang
- /phoenix
- /keyboards
- /rails
- /python
- /js
- /security
- /go
- /swift
- /vim
- /clojure
- /emacs
- /haskell
- /java
- /onivim
- /typescript
- /svelte
- /crystal
- /c-plus-plus
- /kotlin
- /tailwind
- /react
- /gleam
- /ocaml
- /flutter
- /elm
- /vscode
- /ash
- /opensuse
- /html
- /centos
- /php
- /deepseek
- /zig
- /scala
- /textmate
- /lisp
- /sublime-text
- /nixos
- /debian
- /react-native
- /agda
- /kubuntu
- /arch-linux
- /django
- /revery
- /ubuntu
- /manjaro
- /spring
- /nodejs
- /diversity
- /lua
- /deno
- /julia
- /slackware
- /c