4 ms·

Anyone want to explain that code to someone who doesn't know Ruby?

by spydez 19y ago

wvenable 19y ago
I'm not a ruby programmer and it's not immediately obvious what the result would be. I know a pretty large number of languages to the point where, unless it's LISP, I can look at code in any language and have some idea of what it does. When a languages gets "so cool" that it's cryptic than I no longer see the benefit.
- raganwald 19y ago
  Would (1..100).fold(&:+) be more obvious? How about (1..100).reduce(&:+)? If either one of those makes sense, perhaps it is a question of Matz choosing Smalltalk's names for methods (collect, select, detect, reject, inject). Please let me know if changing the name of the method doesn't help.
  - spydez 19y ago
    A little explanation in your article would've been fine. The non-ruby people in the crowd have no clue what "&:+" does, so you lost us really early on when you neglected to explain your fancy one-liner. 'inject' makes sense (in retrospect), but until it was explained, I had no clue why injecting symbol soup into a range of integers was interesting.
    - raganwald 19y ago
      "I had no clue why injecting symbol soup into a range of integers was interesting." Lisp flavours? "A little explanation in your article would've been fine." Done, thank you.
Xichekolas 19y ago
Sums the first 100 integers. You are basically injecting a function (plus in this case) between each element and evaluating it (to describe in very non-technical sense).
- kcl 19y ago
  The same code in k: +/!100 4950 Or if you insist on 1-indexing: +/1+!100 5050
  - Excedrin 19y ago
    What does '/' mean? Also, why does '+' seem to do different things in the first and second expressions? I suppose '!n' means "array of integers ending at n" which seems like an odd choice since it's neither 'not' nor factorial.
    - kcl 19y ago
      '/' in this case is the adverb 'over'. When applied to a function it causes that function to fold over a list. This is the same as inject as far as I know. You are correct in supposing that !n generates an array of integers from 0 to n-1. It is somewhat of an unusual choice for a symbol. I've always thought of it as a factorial 'on the other side'. I don't know if that's what was intended. The k language compresses many old APL functions into symbols like this. Some make sense, some make less sense. You are after all dependent on your keyboard for the range of symbols you can type. In APL the same function was indicated by a lowercase Greek iota. '+' is being used in two different ways. The first way shows it being used in conjunction with an adverb, so '+/' is like a one-argument function that gets applied to the list at the right, but then '+' is inserted between each of the elements of the list because of '/'. '\' is a very similar adverb. It's called 'scan', and it's like 'over', except intermediate output is produced. It can help illustrate what's going on. !100 0 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 .. +/!100 4950 +\!100 0 1 3 6 10 15 21 28 36 45 55 66 78 91 105 120 136 153 171 190 210 231 253 276.. In the second case, '+' is being used as an infix operator, taking two arguments, 1 and !100, so '+' adds 1 to each element in the list 0 to 99, inclusive. This is simply what happens when you add an atom to a list. Each element in the list gets incremented by the value of the atom. Most verbs in k are like this, in that they do what you want, or maybe, they do what they should do if your preference is for something to occur rather than for an error to be thrown. 5 + 0 1 2 5 6 7 5 + !3 5 6 7 1 2 3 + 4 5 6 5 7 9 1 2 + 4 5 6 'length (an error)
gregwebs 19y ago
The way to write this in ruby without extending the symbol class is (1..100).inject { |acc, n| acc + n } inject is a left fold or a reduce- it applies the function {acc + n} to each element in a list (or array) where acc is the result of the last function application. For such a simple function, all we need is the knowledge that we are adding, which is contained in the symbol '+', representing the addition method. So Ideally we would like to write (1..100).inject( :+ ) The semicolon is how you tell ruby you are using a symbol. Yes, you can write a simple sum function, but the point is that this code is more flexible in a very powerful way- we can use other functions then inject and add. Method calling in Ruby is actually message passing. So instead of calling 1.+ 2 # => 3 You can say 1.send( :+, 2 ) # => 3 So we are not trying to convert a symbol to a proc. What we are trying to do is continually send the message ':+' to inject's built in accumulator, with every member of the list (or array) as an argument. In ruby, the brackets are like a function, but it is actually a closure of class Proc. You can convert a different class to a proc (if it supports it) by calling to_proc. Ruby has a syntactic shortcut, '&' for converting to a proc. Normally it actually makes the code clearer because it is also used when passing Procs onto other methods, and is a nice type annotation. So we can hack this syntactic shortcut to create (1..100).inject( &:+ ) So by defining how '&' works by defining to_proc, we can make it create a closure (or Proc) which sends the ':+' symbol, along with any arguments that are yielded to the Proc. In this case, every value from (2..100) is yielded to the Proc. (1 will be the starting value of the accumulator.) You can accomplish a lot of things with a closure, including this hack. But to me this shows that ruby was not designed as a functional programming language, and how by using Ruby's dangerous flexibility you can manage to warp it towards your needs. After learning more languages, Ruby is starting to become pretty ugly to me, but somehow people keep managing to ignore all its faults, make little hacks like these, and be very productive with it.
- raganwald 19y ago
  "After learning more languages, Ruby is starting to become pretty ugly to me, but somehow people keep managing to ignore all its faults, make little hacks like these, and be very productive with it." When I first saw it, I wondered why anyone would want this irregular little language when they could just use Smalltalk or Scheme. An early rant asked why I have to know the difference between a block and a Proc: why the &^(%*)(& do I have to know when to use a block, when to use a Proc, and how to convert between them???

Anyone want to explain that code to someone who doesn't know Ruby?

by spydez 19y ago

Anyone want to explain that code to someone who doesn't know Ruby?

I'm not a ruby programmer and it's not immediately obvious what the result would be. I know a pretty large number of languages to the point where, unless it's LISP, I can look at code in any language and have some idea of what it does. When a languages gets "so cool" that it's cryptic than I no longer see the benefit.

raganwald 19y ago
Would (1..100).fold(&:+) be more obvious? How about (1..100).reduce(&:+)? If either one of those makes sense, perhaps it is a question of Matz choosing Smalltalk's names for methods (collect, select, detect, reject, inject). Please let me know if changing the name of the method doesn't help.
- spydez 19y ago
  A little explanation in your article would've been fine. The non-ruby people in the crowd have no clue what "&:+" does, so you lost us really early on when you neglected to explain your fancy one-liner. 'inject' makes sense (in retrospect), but until it was explained, I had no clue why injecting symbol soup into a range of integers was interesting.
  - raganwald 19y ago
    "I had no clue why injecting symbol soup into a range of integers was interesting." Lisp flavours? "A little explanation in your article would've been fine." Done, thank you.

Xichekolas 19y ago

Sums the first 100 integers. You are basically injecting a function (plus in this case) between each element and evaluating it (to describe in very non-technical sense).

kcl 19y ago
The same code in k: +/!100 4950 Or if you insist on 1-indexing: +/1+!100 5050
- Excedrin 19y ago
  What does '/' mean? Also, why does '+' seem to do different things in the first and second expressions? I suppose '!n' means "array of integers ending at n" which seems like an odd choice since it's neither 'not' nor factorial.
  - kcl 19y ago
    '/' in this case is the adverb 'over'. When applied to a function it causes that function to fold over a list. This is the same as inject as far as I know. You are correct in supposing that !n generates an array of integers from 0 to n-1. It is somewhat of an unusual choice for a symbol. I've always thought of it as a factorial 'on the other side'. I don't know if that's what was intended. The k language compresses many old APL functions into symbols like this. Some make sense, some make less sense. You are after all dependent on your keyboard for the range of symbols you can type. In APL the same function was indicated by a lowercase Greek iota. '+' is being used in two different ways. The first way shows it being used in conjunction with an adverb, so '+/' is like a one-argument function that gets applied to the list at the right, but then '+' is inserted between each of the elements of the list because of '/'. '\' is a very similar adverb. It's called 'scan', and it's like 'over', except intermediate output is produced. It can help illustrate what's going on. !100 0 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 .. +/!100 4950 +\!100 0 1 3 6 10 15 21 28 36 45 55 66 78 91 105 120 136 153 171 190 210 231 253 276.. In the second case, '+' is being used as an infix operator, taking two arguments, 1 and !100, so '+' adds 1 to each element in the list 0 to 99, inclusive. This is simply what happens when you add an atom to a list. Each element in the list gets incremented by the value of the atom. Most verbs in k are like this, in that they do what you want, or maybe, they do what they should do if your preference is for something to occur rather than for an error to be thrown. 5 + 0 1 2 5 6 7 5 + !3 5 6 7 1 2 3 + 4 5 6 5 7 9 1 2 + 4 5 6 'length (an error)

gregwebs 19y ago

The way to write this in ruby without extending the symbol class is (1..100).inject { |acc, n| acc + n } inject is a left fold or a reduce- it applies the function {acc + n} to each element in a list (or array) where acc is the result of the last function application. For such a simple function, all we need is the knowledge that we are adding, which is contained in the symbol '+', representing the addition method. So Ideally we would like to write (1..100).inject( :+ ) The semicolon is how you tell ruby you are using a symbol. Yes, you can write a simple sum function, but the point is that this code is more flexible in a very powerful way- we can use other functions then inject and add. Method calling in Ruby is actually message passing. So instead of calling 1.+ 2 # => 3 You can say 1.send( :+, 2 ) # => 3 So we are not trying to convert a symbol to a proc. What we are trying to do is continually send the message ':+' to inject's built in accumulator, with every member of the list (or array) as an argument. In ruby, the brackets are like a function, but it is actually a closure of class Proc. You can convert a different class to a proc (if it supports it) by calling to_proc. Ruby has a syntactic shortcut, '&' for converting to a proc. Normally it actually makes the code clearer because it is also used when passing Procs onto other methods, and is a nice type annotation. So we can hack this syntactic shortcut to create (1..100).inject( &:+ ) So by defining how '&' works by defining to_proc, we can make it create a closure (or Proc) which sends the ':+' symbol, along with any arguments that are yielded to the Proc. In this case, every value from (2..100) is yielded to the Proc. (1 will be the starting value of the accumulator.) You can accomplish a lot of things with a closure, including this hack. But to me this shows that ruby was not designed as a functional programming language, and how by using Ruby's dangerous flexibility you can manage to warp it towards your needs. After learning more languages, Ruby is starting to become pretty ugly to me, but somehow people keep managing to ignore all its faults, make little hacks like these, and be very productive with it.

raganwald 19y ago
"After learning more languages, Ruby is starting to become pretty ugly to me, but somehow people keep managing to ignore all its faults, make little hacks like these, and be very productive with it." When I first saw it, I wondered why anyone would want this irregular little language when they could just use Smalltalk or Scheme. An early rant asked why I have to know the difference between a block and a Proc: why the &^(%*)(& do I have to know when to use a block, when to use a Proc, and how to convert between them???