List comprehensions are one of Erlang's most powerful tools: learn how you can write quicksort in two lines in a famous example, and more on how to read and write list comprehensions in Erlang's

2011-04-18 · List is the the most important data type in Erlang, as in every (?) functional programming language. We have seen and used lists in almost every previous post. In this post, I will briefly present the “theory” of lists and then present the Erlang’s lists module and its most important functions.

[A || {A,_,_} <- X ]. This is saying that we want to print element A , where A is taken from the tuple As a simple example, suppose I have a list of numbers L and I want to find the first element that is greater than some specific number X. List comprehension puzzler. Hello, Now this I would not expect: 4> S = "123a456". "123a456" 5> is_integer(S). false 6> [is_integer(I) || I <- Intermediate list comprehensions. An important use of List Comprehensions is to help translate prolog into erlang.

Format Se hela listan på learnyousomeerlang.com A list comprehension is a syntactic construct available in some programming languages for creating a list based on existing lists. It follows the form of the mathematical set-builder notation (set comprehension) as distinct from the use of map and filter functions. 2014-09-19 · to get a list of singleton lists and in Haskell [ [x] | x <- [1,2,3] ] gives the same. Erlang also has a syntax for list comprehension, very similar to Haskell’s: [ [X] || X <- [1,2,3] ] The part X <- [1,2,3] above is called the generator expression.

2021-03-04 Implement an Erlang list comprehension that takes two elements from a list and makes a new list of lists. I have this code pair([], Acc) -> lists:reverse(Acc); pair(L, Acc0) -> [ A, B 2021-04-12 Expression The expression specifies the elements of the result. Example: [I || <– [1, 2, 3]] returns the input list element as is.

I don't think it makes a big difference, as tuples are usually small. On the other hand, the list generated by an unfold can be really big (even infinite, and a list comprehension should handle it without problems, if the resulting list is not used and therefore, not generated).

Basically it’s saying “for each list in the list of matches take the head of the list” – a-gigga-wah? Ok. Let’s go to erl. 7> re:run("foo foo bar", "\\b\\w+\\b", [global,{capture,first,list}]). Erlang: List Comprehension, lists:map/2, lists:foreach/2 To use Tag: erlang The effect between List Comprehension and lists:map/2, the latter's performance seem better form my testing.

2011-04-18

Previous message (by thread): [erlang-questions] Parallel List Comprehension Next message (by thread): [erlang-questions] Inets is alive and kicking ;) Messages sorted by: If so, does it imply that using a list comprehension on a semantically unordered set of elements will involve a useless reversal (like lists:reverse/1) of the resulting list? Thanks in advance for any answer, Best regards, Olivier Boudeville.-----Olivier Boudeville Example. List comprehensions are a syntactic construct to create a list based on existing lists. In erlang a list comprehension has the form [Expr || Qualifier1,, QualifierN].

The left side of `||` can be any expression. The right part, `X <- L` is called a generator, and it extracts each element from `L`, one by one. In addition to the generator, a list comprehension can also have one or more filters.
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Erlang is a concurrent and fault tolerant programming language developed at Ericsson While in more common programming languages, such as C or Java, programmers have to use locks and mutexes to write concurrent applications, Erlang uses a message based, shared nothing approach, in which individual threads of execution called processes execute in a concurrent fashion and communicate via message If so, does it imply that using a list comprehension on a semantically unordered set of elements will involve a useless reversal (like lists:reverse/1) of the resulting list? Thanks in advance for any answer, Best regards, Olivier Boudeville.-----Olivier Boudeville Next message: List comprehension or lists:foldl/3 ? Messages sorted by: [ date ] [ thread ] [ subject ] [ author ] On Fri, 13 Feb 2004 00:56:10 -0500 Shawn Pearce < > wrote: > Which is the more preferred form amongst you hacker types? I’ve already talked about this on Inaka’s blog but I thought the list of Erlang battle-stories I’m building here won’t be complete without the story of incomprehensible list comprehensions. Erlang list comprehension optimization.

1> List = [ List comprehensions are a syntactic feature of functional programming languages like Miranda, Haskell, and Erlang which were later copied into Python.
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That is obviously good when it can be done although there are cases when the list must still be created even if it not wanted, for example if the list comprehension is the last thing done in a function so its value must be returned. There is one strange thing further up in the text: "Lists comprehensions still have a reputation for being slow. . They used to be implemented using funs, which

I’ve already talked about this on Inaka’s blog but I thought the list of Erlang battle-stories I’m building here won’t be complete without the story of incomprehensible list comprehensions. Erlang list comprehension optimization.