date: "2024-11-18"
Categories: ["Development", "ruby", "rubylang"]
Tags: ["Development", "Ruby", "Functional"]
at = -> k, a { a[k] }.curry
get = -> meth, a {a.send(meth)}.curry
first = get.(:first)
last = get.(:last)
to_sym = get.(:to_sym)
to_s = get.(:to_s)
map = -> f, a {a.map(&fn)}.curry
map_k = -> f, h { h.transform_keys(f) }.curry
map_v = -> f, h { h.transform_values(f) }.curry
map_h = -> f, h { h.map(&f).to_h }.curry
Sometimes you want to see the first lines of a file.
first = get.(:first)
lines = get.(:lines)
join_lines = get.(:join)
# extract the first n lines of a string
# returns a string
head = -> n { lines >> first.(n) >> join_lines }
my_string = EOF
line 1
line 2
line 3
line 4
EOF
my_string |> head.(2)
line 1
line 2
grow = -> leaf_factory { -> { Hash.new { |h, k| h[k] = leaf_factory.() } } }
a = grow.(grow.(-> { 0 })).call
a[:user][:age] += 1
a[:user][:score] += 5
puts a.inspect
# => {:user=>{:age=>1, :score=>5}}
require "date"
# generate month calendar struct from a date_in_month
month_calendar = ->(date_in_month) {
year = date_in_month.year
month_number = date_in_month.month
first_day_of_month = Date.new(year, month_number, 1)
last_day = Date.new(year, month_number, -1)
start_date = first_day_of_month - first_day_of_month.wday
end_date = last_day + (6 - last_day.wday)
weeks = (start_date..end_date).each_slice(7).map(&:to_a)
[first_day_of_month, weeks]
}
# year struct
year_calendar = ->(date) {
year = date.year
(1..12).each_with_object({}) do |month_number, hash|
first_day, weeks = month_calendar(Date.new(year, month_number, 1))
hash[first_day] = weeks
end
}
# render to text
render_month_text = ->month, fn = ->date { date.day.to_s.rjust(2) } {
first_day_of_month, weeks = month
month_name = Date::MONTHNAMES[first_day_of_month.month]
year = first_day_of_month.year
month_number = first_day_of_month.month
title = "#{month_name} #{year}"
lines = []
lines << title.center(20)
lines << "Su Mo Tu We Th Fr Sa"
weeks.each do |week|
line = week.map do |date|
if date.month == month_number
fn.(date)
else
" "
end
end.join(" ")
lines << line
end
lines.join("
")
}
red = ->a { "[31m#{a}[0m" }
render_date = ->date { date.day.to_s.rjust(2) }
# Example usage
month = month_calendar.(Date.today); 1
puts render_month_text.(month)
# March 2025
# Su Mo Tu We Th Fr Sa
# 1
# 2 3 4 5 6 7 8
# 9 10 11 12 13 14 15
# 16 17 18 19 20 21 22
# 23 24 25 26 27 28 29
# 30 31
cast_val = ->type_cast, value {
if type_cast.respond_to?(:serialize)
# rails 5
type_cast.serialize(value)
else
# rails 4
type_cast.type_cast_from_database(value)
end
}.curry
cast_row = ->result, rec {
types = result.column_types
rec.map { |k, v|
type = types.fetch(k)
[k, cast_val.(type).(v)]
}.to_h
}.curry
conv_result = ->res {
res.to_a.map(&cast_row.(res))
}
query_db = ->db, sql {
res = db.connection.exec_query(sql)
conv_result.(res)
}.curry
quote = ->db, a { db.connection.quote(a) }.curry
db = IsptDb::Base
q = quote.(db)
query = query_db.(db)
query.(%{select "AccountName" from "Customers" WHERE created_at > #{q.(Time.utc(2023, 3, 3))} limit 10})
### Usage
q = quote.(ISPTBase)
query = query_db.(ISPTBase)
query.(%{select "AccountName" from "Customers" WHERE created_at > #{q.(Time.utc(2023, 3, 3))} limit 10})
require "set"
diff_o = diff_h = diff_a = nil #
# Diff two ruby structure
diff_o = ->a, b {
return true if a == b
if a.is_a?(Hash) && b.is_a?(Hash)
diff_h.(a, b)
elsif a.is_a?(Array) && b.is_a?(Array)
diff_a.(a, b)
else
[a, b]
end
}
diff_h = ->h1, h2 {
return true if h1 == h2
delta = (h1.keys + h2.keys).uniq.each_with_object({}) do |k, diff|
diff[k] = diff_o.(h1[k], h2[k])
end.reject { |k, d| d == true }.to_h
delta.empty? ? true : delta
}
diff_a = ->a1, a2 {
return true if a1 == a2
delta = ([a1.size, a2.size].max).times.reduce({}) do |diff, i|
diff[i] = diff_o.(a1[i], a2[i])
diff
end.reject { |k, d| d == true }.to_h
delta.empty? ? true : delta
}
hash_a = {foo: {bar: 1}, baz: [1,2,3]}
hash_b = {foo: {bar: 2}, baz: [1,2,4]}
p diff_o.(hash_a, hash_b)
# => {:foo=>{:bar=>[1, 2]}, :baz=>{2=>[3, 4]}}
array_a = [1, {foo: "bar"}, [1,2]]
array_b = [1, {foo: "baz"}, [1,3]]
p diff_o.(array_a, array_b)
# => {1=>{:foo=>["bar", "baz"]}, 2=>{1=>[2, 3]}}
# @param [a->a] printer: is a function that takes a string and prints it
# @param [Integer] slice: is the number of elements to process before printing
# @return [Enumerable]: is the collection to process
view_progress = ->printer, slice, enum {
start_time = Time.now
index = 0
obj = Object.new
total = enum.count
obj.define_singleton_method(:each) do |&block|
enum.each do |a|
index += 1
if (index % slice) == 0
elapsed = Time.now - start_time
avg = index / elapsed.to_f
total_time = (total.to_f / avg).to_i
printer.("#{index} / #{total}. Elapsed: #{elapsed.to_i}sec. Rate: #{"%0.2f" % avg} entry/sec. Estimated completion time #{start_time + total_time}")
end
block.call(a)
a
end
end
obj.extend(Enumerable)
obj
}.curry
overwriter = ->a { print("\r" + a) ; a }
my_progress = view_progress.(overwriter)
log = ->a { logger.info(a); a}
my_progress = view_progress.(log)
# Usage
10.times.then(&my_progress.(10)).each{|a| sleep 0.05}
Ruby lambdas can be used for documenting code by adding a name to an algorithm.
users.map { |u| u.first_name = " " + u.last_name }
You can use a lambda to make it a bit more clear.
full_name = -> a { a.first_name + a.last_name }
users.map(&full_name)
In this case & calls the to_proc method on lambda.
Here’s another example:
users.select { |a| a.age > 18 }
It can be refactored to
adult = -> a { a.age > 18 }
users.select(&adult)
You can then reuse this adult lambda in combination with other lambdas.
male = -> a { a.gender == :male }
users.select { |a| adult.(a) && male.(a) }
Lambda can also be used for aliasing a method with a name more close to the current context.
If we look at this code:
key = Digest::MD5.hexdigest(Digest::MD5.hexdigest(login) + Digest::MD5.hexdigest(user.keyword))
It can be hard to read, but lets extract the md5 calculation in a lambda:
md5 = -> str { Digest::MD5.hexdigest(str) }
key = md5.(md5.(login) + md5.(user.keyword))
This makes the code clearer and more concise. The signal to noise ratio is much higher this time.
Another way of doing this would be to create a method on the current class. However this is more code and the md5 method definition would be far from its call location even if the method would be use only on the caller method.
When we say simple we don’t mean less powerful.