cyoce / J-uby

J-uby - Ruby with J-like extensions

J-uby aims to augment how Ruby programming with Symbols and Procs works by monkeypatching the aforementioned classes.

Firstly, Symbols are now callable without first calling .to_proc on them. Procs have also gained many more operators.

Tacit programming

Tacit programming is manipulating functions to create other functions without specifying their arguments. A basic example would be a function that adds one to its argument. In Ruby, this would be done with a lambda: ->(x){1+x}. Using the equality (:sym & x).(y) == x.sym(y), we can simplify this lambda to :+ & 1.

Ruby lambdas or expressions can be converted to tacit J-uby code using the following equalities:

sym.(*args) == sym.to_proc.(*args)

(F | G).(*args) == G.(F.(*args))
(F & x).(*args) == F.(x, *args)
(~F).(x) == F.(x,x) # or as many x's as F takes
(~F).(*args) == F.(*args.reverse)
(F + G).(*args) == F.(*args, &G)

F ^ x == F.(x)

F << x == F.(*x)
F.>>(*x) == F.(x)
F.-(x,y) == F.(x).(y)
+F <=> :<< & F

F =~ x == (F.(x) == x)

F / x == x.inject(&F)
F * x == x.map(&F)

F % [G] == F.(&G)

(F**G).(*args) == G.(*args.map(&F))

(F % G).(x)   == F.(x, G.(x))
(F % G).(x,y) == F.(x, G.(y))

(F % [G,H]).(x)   == F.(G.(x), H.(x))
(F % [G,H]).(x,y) == F.(G.(x), H.(y))           # if G and H accept one argument
(F % [G,H]).(x,y) == F.(G.(x,y), H.(x,y))       # if G and H accept 2 arguments

Iteration operators

(F+init).(n) starts an array with init, then applies F to the last init.length entries n times
E.g. fibonacci = :+ + [0,1]

(F**n).(x) iterates F on x n times.

F !~ x iterates F on x until x == F.(x)

Miscellaneous

-:symbol returns the global method by that name. (e.g. (-:puts).("hi") prints "hi")

-array with one argument applies it to the procs in the array. E.g., -[:+ & 1, :* & 2] ^ 4 == [5, 8].

-array with array.length arguments applies each proc to its corresponding argument. E.g., (-[:floor, :ceil]).(1.9, 2.1) == [1,3]

n.- is now the same as n.-@ to save a byte; useful when using a symbol such as :-|(...).

_ is the identity function; for any object o, _[o] == o.

F.& == F.to_proc for any proc F.

D^F is a version of F that can only be used dyadically

M^F is a version of F that can only be used monadically

Aliases

• +some_array == some_array.+ == some_array.length
• +some_string == some_string.+ == some_string.length
• some_number.- == -some_number
• some_number.| == some_number.abs
• Z[any_object] == any_object.to_i
• Q[any_object] == any_object.to_f
• S[any_object] == any_object.to_s
• A[any_object] == any_object.to_a
• H[any_objec] == Hash[any_object]
• _[any_object] == any_object
• int_a !~ int_b == a..b
• some_int.+ == 1..some_int
• some_int.* == 0...some_int
• some_int.to_a == some_int.*
• some_string.to_a == some_string.each_char.to_a
• ~some_string == some_string.reverse
• ~some_array == some_array.reverse

Examples

Join Array with Commas

~:*&?,

(~ :*) & ','                                    # more readable
->(a){ (~ :*).(',', a) }                        # turn `&` into explicit lambda
->(a){ :*.(a, ',') }                            # `(~F).(x,y) == F.(y,x)`
->(a){ a.*(',') }                               # turn symbol call into explicit method call
->(a){ a.join(',') }                            # Array#* is an alias for Array#join

Average of an Array

:/ % [:/ & :+, :size]

->(a){ :/.((:/ & :+).(a), :size.(a)) }          # expand fork to lambda
->(a){ (:+ / a) / a.size }                      # transform `.call`s on procs to method accesses
->(a){ a.reduce(:+) / a.size }                  # expand `F / x` to `x.reduce(&F)`

Haskell-Style foldr from the existing /

Note: as this one is especially complicated, some intermediate steps are omitted

:~|:& &:/|:|&:reverse

(:~ | (:& & :/)) | (:| & :reverse)              # readable
->(f){ (:| & :reverse).((:~ | (:& & :/)).(f)) } # transform to lambda
->(f){ :reverse |  (:/ & ~f) }                  # reduce
->(f){ ->(a){ (:/ & ~f).(:reverse.(a)) } }      # expand `|` into curried lambda
->(f){ ->(a){ ~f / a.reverse } }                # simplify `.call`s

Check if array is all even

:* &:even?|:all?

(:* & :even?) | :all?                           # readable
->(a){ :all?.((:* & :even?).(a))}               # expand | to lambda
->(a){ (:even? * a).all? }                      # simplify explicit symbol calls
->(a){ a.map(&:even?).all? }                    # replace Proc#* with Array#map

Alternative without map

:all?.& &:even?

->(a){ a.all?(&:even?) }