Due to laziness, Haskell types are both inductive and coinductive, or, there is no formal distinguishment between data and codata. All recursive types can contain an infinite nesting of constructors. In languages such as Idris, Coq, Agda, etc. a definition like ones = 1 : ones is rejected by the termination checker. Laziness means that … Read more
Disclaimer: I don’t use Python, so some things I say may be wrong. Python experts, feel free to correct me. Great question. I think the central misconception (if I can’t even call it that; it’s perfectly reasonable how you arrived at the thought process you used) you’re having that prompts you to ask the question … Read more
From the documentation of system() (emphasis/bold mine): The system() library function uses fork(2) to create a child process that executes the shell command specified in command using execl(3) as follows: execl(“/bin/sh”, “sh”, “-c”, command, (char *) 0); system() returns after the command has been completed. During execution of the command, SIGCHLD will be blocked, and … Read more
Let’s do a little trace in our heads of how Haskell will evaluate your expression. Substituting equals for equals on each line, the expression pretty quickly evaluates to True: myAny even [1..] foldr step False [1..] step 1 (foldr step False [2..]) even 1 || (foldr step False [2..]) False || (foldr step False [2..]) … Read more
You can use the second argument of iter(), to call a function repeatedly until its return value matches that argument. This would loop forever as 1 will never be equal to 0 (which is the return value of int()): for _ in iter(int, 1): pass If you wanted an infinite loop using numbers that are … Read more
Very similar to @Eastsun’s, but a bit more intention revealing. Tested in Scala 2.8. scala> val l = List(1, 2, 3) l: List[Int] = List(1, 2, 3) scala> Stream.continually(l.toStream).flatten.take(10).toList res3: List[Int] = List(1, 2, 3, 1, 2, 3, 1, 2, 3, 1) Alternatively, with Scalaz: scala> import scalaz._ import scalaz._ scala> import Scalaz._ import Scalaz._ … Read more
Applying length to unknown lists is generally a bad idea, both practically due to infinite lists, and conceptually because often it turns out that you don’t actually care about the length anyway. You said in a comment: I’m very new to Haskell, so now, don’t infinite structures make my programs very vulnerable? Not really. While … Read more
Functions can access an array-like object called arguments that contains all the arguments that they received function print_my_arguments(/**/){ var args = arguments; for(var i=0; i<args.length; i++){ console.log(args[i]); } }; And you can do the opposite conversion (call a function given a list of arguments) with the apply method: // These are equivalent: print_my_arguments(1,2,3); print_my_arguments.apply(null, [1,2,3]); … Read more
The key here is laziness. If the function you’re using for folding the list is strict, then neither a left fold nor a right fold will terminate, given an infinite list. Prelude> foldr (+) 0 [1..] ^CInterrupted. However, if you try folding a less strict function, you can get a terminating result. Prelude> foldr (\x … Read more