52 questions
1
vote
0
answers
61
views
Haskell PatternSynonyms bang strictness annotation
The User Guide comment says this is not allowed, but the explicitly bidir form is
pattern StrictJust a = Just !a
pattern StrictJust a <- Just !a where
StrictJust !a = Just a
Given that the ...
- 2,806
0
votes
2
answers
45
views
Conflicting definitions in pattern synonyms using a parameter more than once
Why can't I define this pattern synonym?
pattern Double a = (a,a)
error:
• Conflicting definitions for ‘a’
Bound at: <interactive>:1:21
<interactive>:1:23
• ...
- 685
2
votes
3
answers
92
views
Factoring out common constants in pattern synonym code?
I had some code like this:
newtype T = T Text
pattern Alice = T "Alice"
This is fine, but I was using "Alice" in other places. So I decided to factor it out like so:
alice :: ...
- 23.1k
2
votes
1
answer
65
views
Using pattern synonyms to abstract implementation of text type
Lets say I have:
newtype Animal = Animal Text
And I want to be able to pattern match on it like so:
f :: Animal -> (Bool, Text)
f = \case
NonHuman s -> (False, s)
Human -> (True, "...
- 23.1k
1
vote
1
answer
55
views
How to merge nodes that represent synonyms?
Suppose I have a graph like this:
Cytoscape graph
The nodes 'lipid nanoparticle' and 'LNP' are synonyms. How can I identify nodes that represent synonyms and merge them in Cytoscape?
I searched ...
- 21
0
votes
1
answer
278
views
How implement updating index by synonyms without closing index?
I need implement search by synonyms, now it possible todo by
closing index, update index by synonym filter, open index. The probem is that users can update synonym dictanory in any time, and it should ...
- 1
4
votes
1
answer
157
views
Why does using PatternSynonyms trigger a non-exhaustive match warning?
I'm following this answer to learn how to pattern match on Sequences. For concreteness, imagine that I'm implementing breadth-first search over a 2-d grid using a Sequence as a queue. Using just ...
- 3,025
0
votes
1
answer
123
views
How to refactor a Haskell data type with fields into a tagged union of records?
In a large code base, I want to refactor a data type that has constructors with fields into a simple tagged union of records, mainly to better support -Wincomplete-record-updates. It is important ...
- 309
5
votes
0
answers
126
views
Explicit type variable instantiation for pattern synonyms?
Suppose, I have the following code
data F a where
F :: Typeable a => F a
asType :: forall b a. Typeable b => F a -> Maybe (a :~: b, F b)
asType e@F{} = case eqT @b @a of
Just Refl -> ...
- 4,482
2
votes
1
answer
318
views
How to explicitly import 'Fn' pattern from Test.QuickCheck?
Haskell's Test.QuickCheck module exports pattern Fn, which I have been using.
When I import it with:
import Test.QuickCheck
it works fine. However, when I import it with:
import Test.QuickCheck (Fn)
...
- 6,170
2
votes
0
answers
103
views
Generating shingles with synonyms in Elasticsearch
I have a file of alternate spellings for the terms in my index. I want to produce bigrams containing those alternate spellings for particular terms. For example, I have biriyani, biryani, briyani in ...
- 21
4
votes
1
answer
241
views
Pattern synonyms as overloadable 'smart constructors'
There's a fine tradition of including 'smart constructor' methods in an interface (class):
class Collection c a where
empty :: c a
singleton :: a -> c a
-- etc
It would be nice to supply ...
- 2,806
8
votes
1
answer
108
views
Why does my pattern block an error on both sides?
To start off this whole thing I'm working with a pattern synonym defined as follows:
{-# Language PatternSynonyms #-}
pattern x := y <- x @ y
This allows me to run multiple pattern matches across ...
- 4,074
4
votes
1
answer
165
views
Why are recursive pattern synonyms accepted?
This question (from 5 years ago) asks 'Why are all recursive pattern synonyms rejected?' and its example is still rejected. The User Guide says "Pattern synonyms cannot be defined recursively.&...
- 2,806
3
votes
1
answer
150
views
Can a pattern synonym have a different type signature in each direction, like numeric literals do?
Consider the numeric literal 1. It has a different type depending on whether it's used on the left or right of the equals sign. In f True = 1, 1 has type Num p => p. But in f 1 = True, 1 has type (...
1
vote
2
answers
151
views
Design options for constructor constraints: GADT compare PatternSynonym Required
(This is a follow-up to this answer, trying to get the q more precise.)
Use Case Constructors to build/access a Set datatype. Being a set, the invariant is 'no duplicates'. To implement that I need an ...
- 2,806
4
votes
1
answer
188
views
Pattern synonyms signature: Required vs Provided constraints
I think I get it with the "unusual form" of constraints. Just checking ...
The examples in that section for Provided constraints (the second one) all seem to involve GADTs/existentials ...
- 2,806
3
votes
1
answer
550
views
Writing a pattern synonym to hide a constructor
Consider the following:
module MyModule (
A(FortyTwo), -- Note we don't expose PrivateA
B(P) -- Nor PrivateB
) where
pattern FortyTwo = A 42
newtype A = PrivateA Int
data B = PrivateB Int Int
...
- 23.1k
5
votes
1
answer
233
views
No-fun/puzzlement with pattern synonyms as functions
With PatternSynonyms (explicitly bidirectional form), the pattern-to-expr equations in effect form a function but spelled upper-case (providing you end up with an fully saturated data constr of the ...
- 2,806
0
votes
1
answer
124
views
Identifying synonymous rows of a text column in a dataframe using R
Suppose ABC is a dataframe as given below:
ABC <- data.frame(Column1 = c(1.222, 3.445, 5.621, 8.501, 9.302),
Column2 = c(654231, 12347, -2365, 90000, 12897),
...
- 351
0
votes
0
answers
102
views
Patterns and View patterns: am I doing this right
I want to achieve
{-# LANGUAGE PatternSynonyms, ViewPatterns #-}
pattern Just2 :: (Num a, Eq a) => a -> a -> Maybe (a, a)
-- Just2 0 0 ≡ Nothing
-- Just2 x y ≡ Just (x, y)
I think I've ...
- 2,806
0
votes
1
answer
300
views
extracting synonyms using wordnet
I am currently working on my thesis and implementing the solution in R language. i have to find synonyms using word-net dictionary library. i get the synonyms against single word but when i try to get ...
7
votes
1
answer
323
views
Writing a COMPLETE pragma for a polymorphic pattern synonym?
I have the following code and I don't know what should feed at ??. Or cannot polymorphic patterns make complete?
{-# LANGUAGE PatternSynonyms #-}
{-# LANGUAGE ViewPatterns #-}
module Data.Tuple....
- 701
3
votes
2
answers
149
views
Can I capture values from a pattern synonym?
Assuming a pattern:
pattern P :: [Int]
pattern P <- a:_
Can I somehow use a in the function f?
f :: [Int] -> Int
f P = a
The code above generates an error of Not in scope: 'a'.
- 39.3k
0
votes
1
answer
1k
views
Replacing a word by randomly selected synonyms in a string?
I have found the following code in Python that is doing the same work but it only replaces with manually selected synonym.
import nltk
from nltk.corpus import wordnet
synonyms = []
string="i love ...
-1
votes
1
answer
175
views
How to update/save oracle synonyms in database with Python/Django
I am writing a web in Python, I would like to save or update oracle synonyms as select * from synonyms into local database, so the local python program can use those values at regular intervals, I was ...
- 626
3
votes
1
answer
352
views
How to find similar noun phrases in NLP?
Is there a way to identify similar noun phrases. Some suggest use pattern-based approaches, for example X as Y expressions:
Usain Bolt as Sprint King
Liverpool as Reds
- 89
1
vote
0
answers
156
views
Pattern synonyms deriving read?
Pattern synonyms provide a shorthand way to express a value; also they can provide an abstract name to avoid a client module breaking into the data decl. Here's a not very useful one, as an example ...
- 2,806
12
votes
1
answer
1k
views
Haskell: "Qualified name in binding position" error with Map.empty
I'm trying to create a pattern synonym for a newtype with an empty map.
{-# Language PatternSynonyms #-}
import qualified Data.Map as Map
newtype StoreEnv = StoreEnv (Map.Map Int String)
...
- 133
2
votes
1
answer
209
views
Use literal numbers in Fin patterns
On one hand, I can use #_ to construct Fins from literals:
open import Data.Fin
data I'mFinnish : Set where
Mk : Fin 5 → I'mFinnish
foo : I'mFinnish
foo = Mk (# 3)
On the other hand, I can use ...
- 27.6k
2
votes
1
answer
551
views
Using ViewPatterns and PatternSynonyms to simply pattern matches
Lets say I have a GADT for a language like so (my actual language is much more complex, about 50 constructors, but this is a simplified example):
data Expr t where
Add :: Expr t -> Expr t -> ...
- 23.1k
5
votes
1
answer
243
views
How can I write this pattern synonym without ambiguous type errors?
Using ViewPatterns and Data.Typeable, I’ve managed to write a function that allows me to write something resembling case analysis on types. Observe:
{-# LANGUAGE GADTs, PatternSynonyms, RankNTypes, ...
- 43.8k
7
votes
3
answers
2k
views
Haskell pattern matching on vectors
Is it possible to use list style pattern matching on vectors?
ie
import qualified Data.Vector as V
f :: V.Vector a -> a
f (x:xs) = x
gives an error
- 2,021
3
votes
1
answer
104
views
Manually specifying ismorphisms for unidirectional pattern synonym
There probably isn't a way to do this, but I just wanted to ask just in case.
I have a data type that's a simple tuple like this:
data Tup a = T a a
I have a pattern synonym like this:
pattern (:?)...
- 13.6k
6
votes
1
answer
1k
views
How to Pattern Match an Empty Vector in Haskell?
Say I want to implement the length function for lists using pattern matching, then I could do something like this:
length' :: (Num b) => [a] -> b
length' [] = 0
length' (_:xs) = 1 + length' ...
- 1,366
8
votes
1
answer
153
views
Pattern synonym can't unify types within type-level list
I'm getting an error when trying to define a pattern synonym based
on a GADT that has a type-level list.
I managed to boil it down to this example:
{-# LANGUAGE GADTs #-}
{-# LANGUAGE KindSignatures ...
- 88.9k
1
vote
2
answers
294
views
How would we take the last value of a list using colon notation?
Say we have a list in the parameter and pattern match on its head and tail separately so we use x:xs. This means that the inputs are split into a value x and a list xs.
So whatever is before the ...
- 1,189
1
vote
1
answer
2k
views
How to pattern match the end of a list?
Say I wanted to remove all zeros at the end of a list:
removeEndingZeros :: (Num a, Eq a) => [a] -> [a]
removeEndingZeros (xs ++ [0]) = removeEndingZeros xs
removeEndingZeros xs = xs
...
- 365
6
votes
1
answer
223
views
Why are all recursive pattern synonyms rejected?
{-# LANGUAGE PatternSynonyms, ViewPatterns #-}
data Quun = Foo | Bar | Oink Quun
fooey :: Quun -> Bool
fooey Foo = True
fooey (Oink Yum) = True
fooey _ = False
pattern Yum <- (fooey -> ...
- 121k
4
votes
2
answers
687
views
Haskell - Using a constant in pattern matching
Let's say I have the following code (text in <> is a shorthand, not actually part of the code):
data A = <something>
defaultA :: A
defaultA = <Really complicated expression of type A&...
- 5,402
3
votes
1
answer
328
views
Constants in Haskell and pattern matching [duplicate]
How is it possible to define a macro constant in Haskell? Especially, I would like the following snippet to run without the second pattern match to be overlapped.
someconstant :: Int
someconstant = 3
...
- 2,479
11
votes
2
answers
736
views
Pattern matching on a private data constructor
I'm writing a simple ADT for grid axis. In my application grid may be either regular (with constant step between coordinates), or irregular (otherwise). Of course, the regular grid is just a special ...
- 3,116
4
votes
1
answer
350
views
Why can't I pattern match against a ratio in Haskell?
I'm trying to pattern match against a ratio:
isValid :: Ratio Int -> Bool
isValid (num % den) = ...
However, this yields:
Parse error in pattern: num % den
Interestingly, the Data.Ratio package ...
- 1,581
10
votes
1
answer
242
views
Combining patterns
Consider the following data type and pattern synonyms:
{-# LANGUAGE PatternSynonyms, NamedFieldPuns #-}
data Foo = Foo {
a :: Int
, b :: String
, c :: Maybe Bool
}
pattern Bar a b <...
- 131
12
votes
2
answers
2k
views
Pattern matching Data.Sequence like lists
I am using Data.Sequence instead lists for better performance. With lists we can do the following
foo :: [Int] -> Int
foo [] m = m
foo (x:xs) m = ...
How can this be accomplished with Data....
- 1,335
12
votes
1
answer
389
views
A list whose "Nil" carries a value?
Does some standard Haskell library define a data type like this
data ListWithEnd e a = Cons a (ListWithEnd e a)
| End e
That is a list whose terminating element carries a value ...
- 63.3k
5
votes
2
answers
367
views
How to handle lots of constants in Haskell?
I’m working on a library allowing a developper to control a Minitel (the french
videotex terminal).
I have a lot of constant values and I would like to know the best way to manage
them with Haskell. ...
- 1,755
17
votes
1
answer
833
views
Pattern synonyms lead to unexhaustive pattern matching
I've managed to construct the following "minimal" example that shows my problem.
Provided the PatternSynonyms extension is enabled
data Vec = Vec Int Int
pattern Ve x y = Vec x y
f :: (Vec, Vec) -&...
- 4,392
3
votes
2
answers
225
views
Haskell type synonym issue
This gives me the following error
Not in scope: data constructor Blah
Why? I thought that I can use the type synonym everywhere I can use Person
data Person = Person { weight :: Int, height :: ...
- 203
5
votes
2
answers
2k
views
Haskell constructor aliases
Is there a way to have something equivalent to creating "constructor aliases" in Haskell? I'm thinking similar to type aliases where you can give the type a different name but it still behaves in ...
- 71.3k