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Pattern synonyms lead to unexhaustive pattern matching

It is not implemented yet, see #8779. I'm not an expect here, but I know that exhaustiveness checks are hard to implement in a lot of cases, like GADT or guards. Probably it is problematic for pattern synonyms too.

Categories : Haskell

Related to : Pattern synonyms lead to unexhaustive pattern matching
In pattern matching, can I use the matched pattern as is?
If I understand your question correctly, you want to use the heading itself on ???'s place, this can be done using the @ pattern: case first :: rest => first match { case head @ Heading(_,_) => buildPairsAcc(rest, acc, head) case Paragraph(_) // ... other cases Note that this can be used on everything that'll pattern match, including lists: case lst @ head::tail => // do s

Categories : Scala
String Pattern Matching Check in c#
You can use Regex, grouping your patterns: using System; using System.Text.RegularExpressions; class Program { static void Main() { // First we see the input string. string input = "/content/alternate-1.aspx"; // Here we call Regex.Match. Match match = Regex.Match(input, @"content/([A-Za-z0-9-]+).aspx$", RegexOptions.IgnoreCase); // H

Categories : C#
Haskell pattern matching do expression compiler warning
Use a case expression instead: do case "" of [] -> undefined -- or whatever else you want to do (x:xs) -> return x Hope that helps.

Categories : Haskell
Pattern matching in .collect: refer to current element?
Use @ to get a reference to the full object that's being matched. val encodedItems = patterns.collect { case item @ ParsedItem(s, p, o, true) => EncodedItem(encode(s), encode(p, item), encode(o)) }

Categories : Scala
map expression in case clause in scala pattern matching
An expression like that looks like an extractor, hence the message about unapply/unapplySeq methods. If you don't want to use an extractor but just want to match against a plain value, you need to store that value in a stable identifier - you can't use an arbitrary expression as a match case: val case1 = config("c1") x match { case case1 => println("1") ... }

Categories : Scala
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