Example of a WordPress plugin written in a point-free style using PHP Functional Programming Utils

comment-hash.php

<?php

/*
Plugin Name: Comment Hash
Description: Sign comments with a sha256 hash to prevent tampering
Author: Dave Ross
Version: 1.0
Author URI: http://davidmichaelross.com/
*/

// Leaving out the boilerplate that loads & sets up PHP Functional Programming Utils
// See https://github.com/daveross/functional-programming-utils

/**
 * Call a function $fn on $value if $index is odd
 * This is the only function actually written for this plugin
 */
$call_if_index_odd = function( $fn, $value, $index ) {
  return ( 0 === $index % 2) ? $value : $fn( $value );
};

/**
 * Hooks a function into the 'pre_comment_content' filter
 */
$add_pre_comment_content_filter = partially_apply( 'add_filter', 'pre_comment_content' );

/**
 * Returns the sha256 hash of a value
 */
$sha256 = partially_apply( 'hash', 'sha256' );

/**
 * Call $sha256 if $index is odd (uses $call_if_index_odd)
 */
$sha256_if_index_odd = partially_apply( $call_if_index_odd, $sha256 );

/**
 * Implode an array of strings into a single string, separated by spaces
 */
$array_to_string = partially_apply( 'implode', ' ' );

/**
 * Start filling an array from the beginning
 * @param int $count
 * @param mixed $value
 * @return array
 */
$array_fill_from_beginning = partially_apply( 'array_fill', 0 );

/**
 * Creates an array with the same value twice
 * @param mixed
 * @return array
 */
$value_twice_in_array = partially_apply( $array_fill_from_beginning, 2 );

/**
 * Calls array_map for a two-element array, passing an extra parameter with the current $index
 * @param Callable $fn
 * @param Array $a
 * @return Array
 */
$map_over_two_array_entries_with_indexes = partially_apply_right( 'array_map', range( 0, 1 ) );

/**
 * Given a two-element array, call $sha256 on the second element
 * @param Array $a
 * @return Array
 */
$map_sha256_on_second_entry = partially_apply( $map_over_two_array_entries_with_indexes, $sha256_if_index_odd );

/**
 * Append a sha256 hash to the end of a string
 * @param string $x
 * @return string
 */
$append_comment_hash = compose( $array_to_string, $map_sha256_on_second_entry, $value_twice_in_array );

// Register $append_comment_hash as a filter for comment contents
$add_pre_comment_content_filter( $append_comment_hash );