I know by definition higher order functions are functions that receive a function as a parameter or return a function.
I want to know if a nested function is considered a higher order function since there are functions defined inside of it, and if it is the case are nested functions that return a dispatch dictionary considered higher order as well?(they may not receive a function but they do return a dictionary which can activate a function but its not a function up until activation with a correct key).
No, a nested function is not higher-order. As you noted, "higher order functions are functions that receive a function as a parameter or return a function." It is "higher-order" because it is a function that operates on functions. Nesting a function does not do that. It simply modifies its scope. Similarly, a closure (which in most languages has many similarities to a nested function), is not itself a higher-order function.
Related
Is there a way in a where clause in Rust to check if a function passed as a parameter takes specified arguments?
If you're defining a function that takes a function argument, that argument has a very specific type associated with it that dictates the arguments. You cannot call that function with something that doesn't match, it just won't compile.
If you're thinking in terms of dynamic languages where the arguments are somewhat subjective, you're assuming you can make a mistake here and call it incorrectly. You can't. It's strictly disallowed.
My use case is this: a function called 'time' that will return how long it takes to run any function you give it.
So the time function needs to know all the parameters to pass into the function when it calls it.
I know how to pass a function into another function, but how can I pass all its parameters, without knowing in advance how many and what type they are, so they can be used when calling the function?
For example, if I pass in an array of all the parameters I need to send, is there some Dart way to call a function by expanding an array into a list of parameters? Or perhaps there's another way to capture and pass a function call, including all parameters, as one executable object?
I'm also interested in knowing if there's a more Dartful way to accomplish what I'm trying to do re: timing function calls.
I believe using a List of parameters with the apply method is the most common way and practical of doing this and I have seen something similar used to pass parameters for JS interop. As far as I know, there isn't a way to expand an array into a list of parameters like you can for javascript. You could of course create your own object to pass arguments, but I think it would add unnecessary complexity and end up being more difficult.
Example of passing parameters to function in dart:js here.
function call
Per MDN, A function call is an expression that passes control and
arguments (if any) to a function and has the form: expression
(expression-listopt)
callback function
A callback function is a lucky function that gets passed into the enclosing higher-order function: The callback function gets executed (called) inside the higher order function, but not necessarily immediately.
https://thenewstack.io/mastering-javascript-callbacks-bind-apply-call/
function call is term related to program syntax. it related to generally programs and programming languages. There are no predefined semantic, just term which used to describe programs.
callback function is term related to program execution semantic. In some kind callback function is function call with scope, which pass as parameter to another function or method, some parameters of callback function can be free variables and callback function executed generally after method or function in which it was passed.
When i have 3 functions in a program, how do i check a specific function name ?
I want to know the name of those function for the sake of function selection.
Let say linear-kernel function, logistic-kernel function, and non-negative function, when i call the program, one of those function is called and i should to check whether it was linear, logistic or non-negative function, so i can execute another function related with the selected function.
I think doing function selection will save my time from repeating the base code. But doing function selection maybe is not the best design that i could use in Clojure.
FYI, at this level, i already use the "meta" keyword to access the function name, but when i create
(defn isKernel [krn]
(if (= (str (:name (meta #'krn))) "logistic-kernel") 1 0))
The compiler cannot resolve the 'krn' var
In Clojure functions are values, just like the number 4. This is a big part of the underpinnings of much of the language (and functional programming in general). Most of the time we store functions in vars though this is not required. functions as values don't have names* So rather than checking to see if the name of a passed function matches a known name, it makes more sense to ask "does this function have the same value as the function stored in the var" as #cgrand points out this can be accomplished simply by calling =.
If you are doing this kind of dispatch there is a good change that protocols are a better tool than rolling your own
*they do have names for the purpose of creating recursive function literals though thats not what I'm getting at here.
I have read the question Difference between method and function in Scala and many articles about differences between method and function. I got a feeling that a 'method' is just a "named function" defined as a method in a class, a trait or an object. A 'function' represents things like the "anonymous function" or "function literal" or "function object" in those articles. An evidence can be found in the book Programming in Scala http://www.artima.com/shop/programming_in_scala_2ed , page 141, section 8.1, "The most common way to define a function is as a member of some object. Such a function is called a method."
However, when I checked the Scala Language Reference http://www.scala-lang.org/docu/files/ScalaReference.pdf, there are concepts like named method. In page 91, Section 6.20 Return expressions: "A return expression return e must occur inside the body of some enclosing named
method or function." You can also find the term "named function" in the same page and other places.
So my question is, in Scala, do method, named method, and named function refer to the same concept? Where do you get the definition of named function?
In code List(1, 2).map(_ + 1), the original expression _ + 1 is a named method, then the method is converted into a function. What kind of function, anonymous function, function object, named function?
In my understanding, Scala only has two types of function: a named function that is a method; an anonymous function that is a function literal. Function literal is compiled into a function object of trait FunctionN for it to be used in the pure object-oriented world of Scala.
However, for a regular named funciton/method such as _ + 1 in the above code, why does Scala transform it into another function object?
At the language level, there are only two concepts,
Methods are fundamental building blocks of Scala. Methods are always named. Methods live in classes or traits. Methods are a construct native to the JVM, and thus are the same in both Scala and Java. Methods in Scala (unlike functions) may have special features: they can be abstracted over type parameters, their arguments can have default values or be implicit, etc.
Function objects are just instances of a function trait (Function1, Function2, ...). The function is evaluated when the apply method on the function object is called. There is special syntax for defining unnamed "anonymous" functions (aka, "function literals"). A function is just a value, and as such can be named (e.g., val f: (Int => Int) = (x => x)). The type A => B is shorthand for Function1[A, B].
In the linked SO question, it was mentioned that some references (like the Scala spec) use the word "function" imprecisely to mean either "method" or "function object". I guess part of the reason is that methods can be automatically converted to function objects, depending on the context. Note, however, that the opposite conversion wouldn't make sense: a method is not a first-class value that lives on the heap with its own independent existence. Rather, a method is inextricably linked to the class in which it is defined.
The answers to the linked question cover this fairly well, but to address your specific queries:
method => The thing you define with the def keyword
named method => The same, all methods have names
named function => a function that has been assigned to a value, or converted from a method. As contrasted with an anonymous function.
The difference between a method and a Function is somewhat like the difference between an int primitive and a boxed Integer in Java.
In general discussion, it's common to hear both described as being "integers". This normally isn't a problem, but you must take care to be precise wherever the distinction is relevant.
Likewise, a method will be automatically converted to a Function (and therefore an object) when your program demands it, much like boxing a primitive. So it's not entirely wrong to refer to a method as being a function.
UPDATE
So how does it work?
When you attempt to pass a method as the argument to e.g. List[A].map, the compiler will generate an inner class (with a synthetic name) that derives Function1[A,B], and an apply method that delegates to the method you originally supplied. An instance of this will then be passed as the actual argument.