diff options
Diffstat (limited to 'public/make-memoize.html')
| -rw-r--r-- | public/make-memoize.html | 66 |
1 files changed, 0 insertions, 66 deletions
diff --git a/public/make-memoize.html b/public/make-memoize.html deleted file mode 100644 index 8505bef..0000000 --- a/public/make-memoize.html +++ /dev/null @@ -1,66 +0,0 @@ -<!DOCTYPE html> -<html lang="en"> -<head> - <meta charset="utf-8"> - <title>A memoization routine for GNU Make functions — Luke Shumaker</title> - <link rel="stylesheet" href="assets/style.css"> - <link rel="alternate" type="application/atom+xml" href="./index.atom" name="web log entries"/> -</head> -<body> -<header><a href="/">Luke Shumaker</a> » <a href=/blog>blog</a> » make-memoize</header> -<article> -<h1 id="a-memoization-routine-for-gnu-make-functions">A memoization routine for GNU Make functions</h1> -<p>I'm a big fan of <a href="https://www.gnu.org/software/make/">GNU Make</a>. I'm pretty knowledgeable about it, and was pretty active on the help-make mailing list for a while. Something that many experienced make-ers know of is John Graham-Cumming's "GNU Make Standard Library", or <a href="http://gmsl.sourceforge.net/">GMSL</a>.</p> -<p>I don't like to use it, as I'm capable of defining macros myself as I need them instead of pulling in a 3rd party dependency (and generally like to stay away from the kind of Makefile that would lean heavily on something like GMSL).</p> -<p>However, one really neat thing that GMSL offers is a way to memoize expensive functions (such as those that shell out). I was considering pulling in GMSL for one of my projects, almost just for the <code>memoize</code> function.</p> -<p>However, John's <code>memoize</code> has a couple short-comings that made it unsuitable for my needs.</p> -<ul> -<li>Only allows functions that take one argument.</li> -<li>Considers empty values to be unset; for my needs, an empty string is a valid value that should be cached.</li> -</ul> -<p>So, I implemented my own, more flexible memoization routine for Make.</p> -<pre><code># This definition of `rest` is equivalent to that in GMSL -rest = $(wordlist 2,$(words $1),$1) - -# How to use: Define 2 variables (the type you would pass to $(call): -# `_<var>NAME</var>_main` and `_<var>NAME</var>_hash`. Now, `_<var>NAME</var>_main` is the function getting -# memoized, and _<var>NAME</var>_hash is a function that hashes the function arguments -# into a string suitable for a variable name. -# -# Then, define the final function like: -# -# <var>NAME</var> = $(foreach func,<var>NAME</var>,$(memoized)) - -_main = $(_$(func)_main) -_hash = __memoized_$(_$(func)_hash) -memoized = $(if $($(_hash)),,$(eval $(_hash) := _ $(_main)))$(call rest,$($(_hash)))</code></pre> -<p>However, I later removed it from the Makefile, as I <a href="https://projects.parabola.nu/~lukeshu/maven-dist.git/commit/?id=fec5a7281b3824cb952aa0bb76bbbaa41eaafdf9">re-implemented</a> the bits that it memoized in a more efficient way, such that memoization was no longer needed, and the whole thing was faster.</p> -<p>Later, I realized that my memoized routine could have been improved by replacing <code>func</code> with <code>$0</code>, which would simplify how the final function is declared:</p> -<pre><code># This definition of `rest` is equivalent to that in GMSL -rest = $(wordlist 2,$(words $1),$1) - -# How to use: -# -# _<var>NAME</var>_main = <var>your main function to be memoized</var> -# _<var>NAME</var>_hash = <var>your hash function for parameters</var> -# <var>NAME</var> = $(memoized) -# -# The output of your hash function should be a string following -# the same rules that variable names follow. - -_main = $(_$0_main) -_hash = __memoized_$(_$0_hash) -memoized = $(if $($(_hash)),,$(eval $(_hash) := _ $(_main)))$(call rest,$($(_hash)))</pre> -<p></code></p> -<p>Now, I'm pretty sure that should work, but I have only actually tested the first version.</p> -<h2 id="tldr">TL;DR</h2> -<p>Avoid doing things in Make that would make you lean on complex solutions like an external memoize function.</p> -<p>However, if you do end up needing a more flexible memoize routine, I wrote one that you can use.</p> - -</article> -<footer> -<p>The content of this page is Copyright © 2014 <a href="mailto:lukeshu@sbcglobal.net">Luke Shumaker</a>.</p> -<p>This page is licensed under the <a href="http://www.wtfpl.net/txt/copying/">WTFPL-2</a> license.</p> -</footer> -</body> -</html> |