Questions tagged [value-constructor]
10 questions
12
votes
2 answers
What is the difference between value constructors and tuples?
It's written that Haskell tuples are simply a different syntax for algebraic data types. Similarly, there are examples of how to redefine value constructors with tuples.
For example, a Tree data type in Haskell might be written as
data Tree a =…
ely
- 74,674
- 34
- 147
- 228
11
votes
2 answers
Why can't i re-use same value constructor among different data types?
i am new to Haskell and probably missing something really basic here, but i am not able to re-use same value constructor among different data types.
data Colour = Red | Pink | Orange | Yellow
data Fruit = Apple | Orange | Banana
This produces…
user17472
- 139
- 9
8
votes
1 answer
Why am I able to use my value constructor even though I don't export it?
For practice, I'm implementing a queue data type in a module called "Queue". My data type is also called "Queue", as is its only value constructor:
module Queue (Queue, enq, emptyQueue) where
data Queue a = Queue {
inbox :: [a],
outbox ::…
jub0bs
- 60,866
- 25
- 183
- 186
3
votes
3 answers
data type with a default field and that needs a function that works with it
Say, I have a data type
data FooBar a = Foo String Char [a]
| Bar String Int [a]
I need to create values of this type and give empty list as the second field:
Foo "hello" 'a' []
or
Bar "world" 1 []
1) I do this everywhere in my code…
akonsu
- 28,824
- 33
- 119
- 194
2
votes
2 answers
How to define a function that takes natural numbers of a data type and return their sum?
I am still learning how value constructors work. I read a lot about data types and their value constructors. The problem is that I never saw them in practice. For example
data Nat = Zero | Succ Nat
Now if we want to define a functions that takes…
Cara
- 165
- 1
- 4
- 15
1
vote
1 answer
Value constructors in haskell
I have a question about Haskell. I'm new so I don't understand too well, but if anyone could help me I'd really appreciate. I have this exercise from a book that I bought.
Create a type Question with value contructors Sim or Nao. Make a
function…
Marrows
- 127
- 1
- 11
1
vote
0 answers
Define function independent of specific value constructor (templates?)
Is it possible to write a function for generic types (in this case applicatives) without making assumptions about the name of type constructors?
I can write the following:
f :: Maybe a -> Maybe a
f (Just a) = (Just a)
That one works on Maybes and…
lo tolmencre
- 3,804
- 3
- 30
- 60
1
vote
1 answer
Why are types declared in value constructors not types in Haskell?
Suppose I have the following value constructor:
data Shape = Circle Float Float Float | Rectangle Float Float Float Float
Now I can run:
ghci> :t Circle
Circle :: Float -> Float -> Float -> Shape
Now I can write a type declaration
surface :: Shape…
hawkeye
- 34,745
- 30
- 150
- 304
0
votes
1 answer
Working with value constructors in Haskell
I'm quite stuck in this exercise, the program should receive an input like:
dividing (Number 50) (Number 10)
And then output something like:
Number 10
I tried this:
data Number = Ok Double | Error String deriving Show
dividing :: Number ->…
devinho
- 404
- 4
- 18
0
votes
1 answer
Default and value constructed objects have different types
Consider the following code with one variable default constructed and the other one value constructed:
#include
#include
struct A
{
A() : m_() {}
A(int m) : m_(m) {}
int m_;
};
int main()
{
A a, b(), c(5);
…
Erwin411
- 734
- 1
- 7
- 14