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Questions tagged [non-exhaustive-patterns]

This tag concerns pattern match coverage errors or warnings in functional programming languages with algebraic data types and pattern matching. Questions with this tag can be about why a compiler detects missing patterns or why missing patterns cause an error at run time.

85 questions
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Non-exhaustive pattern matches only because I left off `otherwise =`?

I wrote a simple program in Haskell that plays the guessing game described in The Rust Programming Language book: Here’s how it works: the program will generate a random integer between 1 and 100. It will then prompt the player to enter a guess.…
evanrelf
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Pattern match(es) are non-exhaustive

I'm trying to create a function that eliminates multiples of a given Integer from a list of Integers, in the form multiples x [y], where x is the given Integer, and y is the list. Here's what I have: multiples :: Integer -> [Integer] ->…
Erakura
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Pattern Match Fail when `function [] _ = ...; function _ [] = ...` syntax is omitted

Though disjoint exhausts all possible patterns in its guard conditions, Haskell gives me a PatternMatchFail error when running it. disjoint :: (Ord a) => [a] -> [a] -> Bool disjoint l@(x:xs) r@(y:ys) | null l || null r = True | x == y …
Nicholas Montaño
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Haskell: Fix non-exuastive patterns in function

I have a program that traverses an AST and returns a map of the functions and variables used and how many times they occurred. Here it is: import Data.Map import Language.Haskell.Exts.Syntax increment :: Ord a => a -> Map a Int -> Map a…
user2548080
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Make Compile Fail on Non-Exhaustive Match in Scala 3

Since Scala 2.13, -Wconf compiler flag allows to precisely control over which warnings should be handled as errors. The configuration string for -Wconf however is not always the same when migrating to Scala 3. In particular, I'm struggling to find…
alessandro candolini
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Multiple assignment from a vector to individual variables

In my test suite I am frequently writing code such as val Vector(socialSci, humanities, pureSci, pureApplSci) = foo(someValue) foo obviously returns a (short) Vector but I'd like to have names for each of the values. It's not always four items…
bwbecker
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Non Exhaustive Patterns in function

I'm writing a program in Haskell that can pretty print a table and do basic queries on it. The following function is a snippet of the code which prints a table: printTable :: Table -> [String] printTable table@(header:rows) = [addLine] ++ addHeader…
Felix
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Haskell, Non-exhaustive patterns in function - way for checking this condition

Is there exist any way to check if my code contains: Non-exhaustive patterns in function ? Maybe some flag for compiler ?
user6023611
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Haskell: Non-exhaustive patterns with Sieve of Eratosthenes

I wanted to use this code of Sieve of Eratosthenes from this page: http://en.literateprograms.org/Sieve_of_Eratosthenes_(Haskell)#chunk def:primes_naive Only a bit modified, so it only shows the primes up to a number: primes :: Integral a => a ->…
Rainflow
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Haskell non-exhaustive patterns in function with `otherwise`

I am using the following function: combinations :: Int -> [a] -> [[a]] combinations k xs = combinations' (length xs) k xs where combinations' n k' l@(y:ys) | k' == 0 = [[]] | k' >= n = [l] | null l = [] …
Marcin
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Non-exhaustive pattern in function-Haskell

I've written a function, that Inserts an Element into a binary Tree, but every time I try to run it, I get the a non-exhaustive pattern in function. type Eintrag = (Person, Anschrift, SozNr) data Tree = Nil | Node Eintrag Tree Tree deriving (Eq,…
Irina Avram
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Calculating the length of an array in haskell - non exhaustive patterns error

I've searched around on here and on the net in general and I can't find anything that seems to be answering this question. I've only just starting playing around with Haskell for a module at university and I'm having an issue defining a function to…
leachrode
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Why does Scala 2.10 give 'match may not be exhaustive' warning when matching on singleton types?

In Scala 2.10.0-M4 object X def f(e: Either[Int, X.type]) = e match { case Left(i) => i case Right(X) => 0 } gives: warning: match may not be exhaustive. It would fail on the following input: Right() Is this correct? Surely the match is…
Scott Morrison
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Disable "Non-exhaustive patterns in case" in GHCI

I am reading the paper "Monad Transformers Step by Step" and making my way through the examples. In the eval0 example, there is an intentional non-exhaustive pattern in a case expression: eval0 :: Env -> Exp -> Value eval0 env (Lit i) = IntVal…
Ralph
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Unreachable case except for null in scala

I have the following helper function. I am trying to create a word frequency List. (a,b,a) => [(a,2),(b,1)]: def add_to_lop(c:Char, lop: List[(Char, Int)]):List[(Char, Int)] = { lop match { case List() => List((c,1)) case (c,…
figs_and_nuts
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