# Does Haskell have pattern matching?

## Does Haskell have pattern matching?

Overview. We use pattern matching in Haskell to simplify our codes by identifying specific types of expression. We can also use if-else as an alternative to pattern matching. Pattern matching can also be seen as a kind of dynamic polymorphism where, based on the parameter list, different methods can be executed.

## How do you do pattern matching in Haskell?

You do that by putting a name and an @ in front of a pattern. For instance, the pattern xs@(x:y:ys). This pattern will match exactly the same thing as x:y:ys but you can easily get the whole list via xs instead of repeating yourself by typing out x:y:ys in the function body again.

**What is pattern matching in Haskell explain with example?**

In a functional language, pattern matching involves checking an argument against different forms. A simple example involves recursively defined operations on lists. I will use OCaml to explain pattern matching since it’s my functional language of choice, but the concepts are the same in F# and Haskell, AFAIK.

### What is a record in Haskell?

Records are an extension of sum algebraic data type that allow fields to be named: data StandardType = StandardType String Int Bool –standard way to create a product type data RecordType = RecordType — the same product type with record syntax { aString :: String , aNumber :: Int , isTrue :: Bool }

### What is Fmap in Haskell?

You can think of fmap as either a function that takes a function and a functor and then maps that function over the functor, or you can think of it as a function that takes a function and lifts that function so that it operates on functors. Both views are correct and in Haskell, equivalent.

**What is a type in Haskell?**

In Haskell, every statement is considered as a mathematical expression and the category of this expression is called as a Type. You can say that “Type” is the data type of the expression used at compile time.

## What is a data type in Haskell?

From HaskellWiki. In Haskell, types are how you describe the data your program will work with.

## What is FST in Haskell?

Type: (a,b) -> a. Description: returns the first item in a tuple.

**Is Fmap a functor?**

The expression fmap (*2) is a function that takes a functor f over numbers and returns a functor over numbers. That functor can be a list, a Maybe , an Either String, whatever. The expression fmap (replicate 3) will take a functor over any type and return a functor over a list of elements of that type.

### What are the various types of pattern matching algorithm?

Single-pattern algorithms

Algorithm | Preprocessing time | Matching time |
---|---|---|

Boyer–Moore | Θ(m + k) | Ω(n/m) at best, O(mn) at worst |

Two-way algorithm | Θ(m) | O(n) |

Backward Non-Deterministic DAWG Matching (BNDM) | O(m) | O(n) |

Backward Oracle Matching (BOM) | O(m) | O(mn) |

### How do you specify a type in Haskell?

Haskell has three basic ways to declare a new type:

- The data declaration, which defines new data types.
- The type declaration for type synonyms, that is, alternative names for existing types.
- The newtype declaration, which defines new data types equivalent to existing ones.

**How do you find type in Haskell?**

If you are using an interactive Haskell prompt (like GHCi) you can type :t and that will give you the type of an expression. e.g. or e.g.

## How do you declare data types in Haskell?

By using record syntax to create this data type, Haskell automatically made these functions: firstName, lastName, age, height, phoneNumber and flavor.

- ghci> :t flavor.
- flavor :: Person -> String.
- ghci> :t firstName.
- firstName :: Person -> String.

## What kind of functions are FST and SND?

The types of fst and snd . Functions like fst and snd , which can handle arguments of any type are called (parametric) polymorphic functions.

**What is curry in Haskell?**

From HaskellWiki. Currying is the process of transforming a function that takes multiple arguments in a tuple as its argument, into a function that takes just a single argument and returns another function which accepts further arguments, one by one, that the original function would receive in the rest of that tuple.

https://www.youtube.com/watch?v=xkFjSuiI8x8