Feature #9401: Yet another syntax for literal anonymous functions (lambdas)

• Status: Open
• Assignee: -
• Target version: -

[alexeymuranov (Alexey Muranov)]

Please do not be angry at me and just close this proposal if it does not look interesting. It comes from my aesthetic dissatisfaction with the ->(x){ ... } literal anonymous function notation and from my amateurish interest in lambda calculus.

Here is a yet another syntax for literal anonymous functions (lambdas) that i propose:

f = {\ x => x*x }
f[1] # => 1
f[2] # => 4

It looks a bit like a hash on purpose: i think that a hash is a "function in extension" and a lambda is a "function in intension" (see, for example, in these notes). The backslash stands for "lambda", like in Haskell.

[alexeymuranov (Alexey Muranov)]

An anonymous "function" (not really a function) without arguments would be like this:

timer = {\=> Time.now }

---

Maybe there is no need to make it look so much like a hash, so the following looks to me like a good option either:

f = {\ x -> x*x }
timer = {\-> Time.now }

[alexeymuranov (Alexey Muranov)]

I have realized that the backslash may conflict with explicit line continuation. In that case, "almost any" symbol would work to distinguish a "lambda" from a hash. For example: {^ x => x*x }. (I've read that initially Church wrote x̂ -- "x-hat", and not λx.)

[nobu (Nobuyoshi Nakada)]

What about (^x) {x*x}?

[alexeymuranov (Alexey Muranov)]

Nobuyoshi Nakada wrote:

What about (^x) {x*x}?

I think, my initial attempt was closer to lambda calculus notation (λx(x*x)) or (λx.x*x), to its modern variant x ⟼ x*x, to Haskell \x -> x*x, to Ruby block syntax {|x| x*x }, and to Ruby hash syntax { 2 => 2*2 }.

Another option: make it openly similar to the block syntax: {\|x| x*x } or {^|x| x*x }. Other options:

• {<x> x*x }, {<> Time.now },
• {<x>=> x*x },
• {|x|=> x*x },
• {|x|> x*x } be a proc and {|x|-> x*x } be a lambda.

Also, a double backslash would not conflict with a line break:

• {\\ x => x*x }, {\\=> Time.now }.

Sorry, i cannot choose myself the best syntax, i just do not like ->(x){ ... } (strange placement of the "arrow", and it looks like a method call with a block, but the block parameters are mysteriously missing from the block and are found outside in parentheses, where arguments would be expected).

Edited 2014-04-03

[hsbt (Hiroshi SHIBATA)]

• Project changed from 14 to Ruby master