12.3.1 Haskell

• Haskell is a statically typed, purely functional programming language
• Lazy evaluation in Haskell means expressions are evaluated only when their values are needed.
• Haskell uses type inference to often infer the types of variables and expressions
• In Haskell, data is immutable, meaning it cannot be changed once created.
• The functional paradigm in Haskell makes programs easier to reason
• Static typing in Haskell reduces runtime type errors.
• Lazy evaluation in Haskell improves performance
• What does the Haskell function `doubleMe x = x + x` do?

  Doubles the input
• Haskell is a purely functional programming language, meaning programs are composed of pure functions
• Haskell's static typing checks types at compile time.
• Haskell is a statically typed language where types are checked at compile
• Haskell programs are composed of pure functions.
• What are three other key features of Haskell besides static typing and pure functions?

  Lazy evaluation, type inference, immutable data
• Order the Haskell features from most to least frequently mentioned in the study material.

  1️⃣ Functional paradigm

  2️⃣ Static typing

  3️⃣ Lazy evaluation
• Lazy evaluation improves performance by evaluating expressions only when needed.
• Lazy evaluation ensures that expressions are evaluated only when their values are needed.
• What is the result of the Haskell expression `doubleMe 5` where `doubleMe x = x + x`?

  $10$
• Haskell's type inference allows it to often infer the types of variables and expressions
• Match the Haskell feature with its benefit:

  Immutable data ↔️ Prevents unexpected side effects

  Type inference ↔️ Simplifies code
• What does the Haskell function `doubleMe x = x + x` do?

  Doubles its input
• A type signature like `Int -> Int` means the function takes an integer and returns an integer.
• What are the three types of expressions in Haskell?

  Value, function, operators
• The expression 2 + 3</latex> in Haskell evaluates to $5$.
• Declarations in Haskell introduce new identifiers
• What does the declaration $x =$$5$ in Haskell do?


  Assigns value 5 to x
• Steps to define a function in Haskell

  1️⃣ Declare the function name

  2️⃣ Specify the type signature

  3️⃣ Define the function parameters

  4️⃣ Write the function expression
• What does the function $doubleMe :: Int - > Int$ do?


  Doubles an integer
• A type signature $Int - > Int$ means the function takes an integer and returns an integer.
• A single-line comment in Haskell starts with --
• What type does Haskell infer for $x =$$42$?


  `Int`
• Pure functions in Haskell always return the same output for the same input.
• Haskell uses lazy evaluation, which means expressions are evaluated only when their values are needed
• What is one benefit of static typing in Haskell?

  Fewer runtime errors
• Haskell can automatically infer the types of variables and expressions.
• What is the functional paradigm in Haskell focused on?

  Pure functions
• The function $doubleMe :: Int - > Int$ in Haskell doubles an integer
• Single-line comments in Haskell start with `--`.
• What type does Haskell infer for $y =$$3.14$?


  `Double`
• Recursion in Haskell ensures pure functional behavior by not modifying state.
• To define a recursive function in Haskell, you need a base case and a recursive step