change block to Proc

[moba1]

Contents of change

Changed following methods which received &block to receive Proc.

• value_or
• fmap
• bind
• map_or

Reason

In the current code, following code can not run correctly:

Left.new(1).fmap {|x| x + 1}

The cause lies with Crystal compiler can't infer function type(compiler can't infer T of &block : T -> U).
So instead of receiving a &block, change it to receive a Proc.
As a result, value_or(&block : ->U) was deleted because it became impossible to overload.

[alex-lairan]

In Crystal a Block is like a Proc, but with a simpler syntax.

Why not allow both ?

Edit : sorry, I've read the reason.
Maybe there is a way to have both worlds. I will try myself today.

[alex-lairan]

I tried and got this :

icr(0.26.1) > require "./src/monads"
 => ok
icr(0.26.1) > left = Monads::Left.new(5)
 => Monads::Left(Int32){5}
icr(0.26.1) > left.fmap { |x| x * 2 }
 => Monads::Left(Int32){5}
icr(0.26.1) > left.fmap(->(x : Int32) { x * 2 })
 => Monads::Left(Int32){5}
icr(0.26.1) > right = Monads::Right.new(5)
 => Monads::Right(Int32){5}
icr(0.26.1) > right.fmap { |x| x * 2 }
 => Monads::Right(Int32){10}
icr(0.26.1) > right.fmap(->(x : Int32) { x * 2 })
 => Monads::Right(Int32){10}

And for Crystal 0.28

icr(0.28.0) > require "./src/monads"
 => ok
icr(0.28.0) > left = Monads::Left.new(5)
 => Monads::Left(Int32){5}
icr(0.28.0) > left.fmap { |x| x * 2 }
 => Monads::Left(Int32){5}
icr(0.28.0) > left.fmap(->(x : Int32) { x * 2 })
 => Monads::Left(Int32){5}
icr(0.28.0) > right = Monads::Right.new(5)
 => Monads::Right(Int32){5}
icr(0.28.0) > right.fmap { |x| x * 2 }
 => Monads::Right(Int32){10}
icr(0.28.0) > right.fmap(->(x : Int32) { x * 2 })
 => Monads::Right(Int32){10}

Can you give me your errors ?

[moba1]

I implement following code :

class Left(E) < Either(E, Nil)
  def fmap(&block : T -> U) forall T, U
    self
  end
end

This code was implemented for the purpose of enabling execution of the same block with Right(T) and Left(E):

# a is Left(String) or Right(Int32)
a.fmap {|x| x + 1}

But, if a is Left (String), Crystal can't run this correctly under the current code.
Also, in the above implementation, Crystal can't infer what type comes to fmap first argument, and Crystal compiler has bug in type inference: T == Nil.
As a result, Crystal can't infer type T correctly even with the above implementation, and return error: undifned method '+' for Nil.

[moba1]

I asked Forum whether Crystal can infer T from &block : T-> U under the code that returns self like the above.
Then I got answer that T should not be able to infer in the above code.

[alex-lairan]

Got it !

I opened an issue : #26