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.
Questions tagged [non-exhaustive-patterns]
85 questions
0
votes
2 answers
Haskell - "Non-exhaustive patterns" error with a function using list
I'm trying to make a function in haskell to know if all the elements in a list of list have the same length. (I've search answers in previous posts but none of them works).
sameLength :: [[t]] -> String
sameLength [] = "Empty list"
sameLength…
Prygan
- 95
- 1
- 9
0
votes
1 answer
Non-exhaustive patterns in function trace'
trace :: String -> Float -> Colour -> [ColouredLine]
trace (c:cs) angle colour
= trace' (c:cs) angle colour (0.0,0.0)
where
trace' "" angle colour intvertex = []
trace' (c:cs) angle colour intvertex
| c == 'R' = trace' cs…
overpro
- 49
- 8
0
votes
1 answer
Non-exhaustive on Haskell recursion
sumAllDigits :: [ Int ] -> Int
sumAllDigits (x:xs)
|(x:xs) == [] = 0
|x >= 10 = sumDigits x + sumAllDigits xs
|x< 10 = x + sumAllDigits xs
REPORT:
*Recursion> sumAllDigits [22,33]
*** Exception:…
overpro
- 49
- 8
0
votes
1 answer
Non-exhaustive pattern in function declaration
I'm having difficulties implementing the following function:
type Tabuleiro = [String]
type Comandos = String
type Comando = String
type Coordenadas = String
novaCoord :: Tabuleiro -> Comandos -> Coordenadas -> Coordenadas
novaCoord l (cmd:xs)…
skills
- 315
- 5
- 17
0
votes
1 answer
Non-exhaustive patterns in function error
In haskel, I got an error and somehow I couldn't find the right solution. There is the error i get and my code:
My code:
data MyTree = Leaf Float | Tree String MyTree MyTree deriving (Show, Eq, Ord)
asgCodeRec1 [] _ = []
asgCodeRec1 (a:b:c) (y:ys)…
Bora
- 1,402
- 16
- 19
0
votes
1 answer
Exception : Pattern Matching failure Haskell
I am trying to implement Standard words function of Haskell. I am using State Monad to solve the problem.
My Code is :
type WorS = ([String],String,String)
words' :: State WorS [String]
words' = do
(lwords, words, x:xs) <- get
…
Deepali Semwal
- 139
- 1
- 2
- 9
0
votes
2 answers
Haskell: Non-exhaustive patterns in function (simple functions)
I am confused as to why the 1st and 3rd versions of this functions give this error whereas the second definition works fine.
-- head and tail
third :: [a] -> a
third [a] = head (tail (tail[a]))
-- Pattern matching
third2 :: [a] -> a
third2…
BradStevenson
- 1,974
- 7
- 26
- 40
-1
votes
1 answer
Non-exhaustive patterns in function Exception in haskell
I have this code:
import Data.Char
foo :: String -> String
foo (x:xs) = if (digitToInt(x)) == 0
then foo xs
else if (digitToInt(x)) /= 0
then replicate (digitToInt(x)) (head $…
nEYncI
- 3
- 2
-1
votes
3 answers
Fatal error: exception Match_failure("main.ml", 8, 15)
Here is my code:
type 'a tree = Empty | N of 'a * 'a tree * 'a tree
let absolute x =
if x > 0 then x
else -x
let rec node = function
| N(_, Empty, Empty) -> 1
| N(_, g, d) -> 1 + node g + node d
let rec balanced = function
…
obla
- 123
- 2
- 7
-1
votes
1 answer
Keep getting matching error in haskell when testing function
this is the function
toRevDigits :: Integer -> [Integer]
toRevDigits 0 = []
toRevDigits x
| x<0 = []
| otherwise = lastDigit x:(toRevDigits (dropLastDigit x))
this is the test
testRevDigits :: (Integer, [Integer]) -> Bool
testRevDigits…
Spencer Josephs
- 21
- 1
- 5