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@mjwillson
mjwillson / tax_bands.hs
Created October 29, 2009 22:35
Pure functional tax bands
infinity = 1.0/0
savingsIncomeTax200910 = [(0, 6475), (0.1, 8915), (0.2, 43875), (0.4, infinity)]
incomeTax200910 = [(0, 6475), (0.2, 43875), (0.4, infinity)]
taxWithBands bands income
= if income <= threshold then
rate * income
else
rate * threshold + taxWithBands loweredRemainingBands remainingIncome
where
@mjwillson
mjwillson / merb_restful_rangeable_collections.rb
Created March 6, 2009 17:14
RESTful way of exposing a collection resource in merb in a pageable / sub-range-fetchable way. Supports HTTP Content-Range
# Drop me a line if you wanna see this as a proper merb plugin.
class Merb::Controller
ITEM_RANGE = /^items=(\d+)-(\d+)$/
RANGE = /^(\d+)-(\d+)$/
# Displays a collection resource (using Merb's display method) while supporting requests for sub-ranges of items in a RESTful fashion.
# This supports a subset of the HTTP/1.1 spec for content ranges, using a custom range unit 'items'. eg:
# GET /collection HTTP/1.1
# Range: items 10-20
@mjwillson
mjwillson / yaml_fixtures.rb
Created November 20, 2008 23:55
Some general-purpose fixture-loading code which supports references and respects dependencies. Quite short as it hooks into yaml.rb to do most of the work
# This is a mixin for Test::Unit::TestCase, for providing tests with a simple facility to load fixtures from
# YAML files. It aims to do as much as possible in a generic way with the YAML library rather than couple
# tightly to a database library.
#
# Fixtures can use arbitrary YAML to represent ruby objects, using !ruby/object:Some::ClassName where needed.
# you will typically need to implement yaml_initialize on the relevant class, in order for this to
# work in the way you desire (we do so here for Sequel::Model; others including ActiveRecord shouldn't be hard)
#
# Data within one fixture can refer to other fixtures by file and name, using the syntax: !fixture file/name.
# this is achieved by adding a special YAML domain type.
@mjwillson
mjwillson / equivalence_relation.rb
Created November 13, 2008 17:05
Simple Ruby class for an extensionally-specified Equivalence Relation with fast lookup
require 'set'
class EquivalenceRelation
def initialize
@equivalence_class_by_member = {}
end
def declare_equivalent(*items)
combined_equivalence_class = items.map {|item| equivalence_class_of(item)}.inject(Set.new) {|accum,set| accum.union(set)}
combined_equivalence_class.each {|member| @equivalence_class_by_member[member] = combined_equivalence_class}
end