First class functions

• an essential feature of functional language

• Functions are described as first-class when they can be treated like any other value: that is to say,

  • they can be dynamically assigned to a name or symbol at runtime

  • they can be stored in data structures

  • passed in via function arguments

  • returned as function return values

• Similar to how pointers work

• Also called Lambdas

  • lambdas are unnamed/annoymous functions

  • The point of a lambda function is where you need a function in that place and only there; since it is not needed anywhere else you simply define it right there. It doesn’t need a name.

    • If you did need to reuse it somewhere else then you would consider defining it as a named function and referencing it by name instead

• As function/lambda is passed as a variable (or is function form)

  • it is not called immediately

  • it can be called/invoked by whoever it was passed to

• First-class functions are also the means for achieving asynchronous I/O

  • allows to make non-blocking function call

  • you pass it a reference to a function for it to call you back on when it is done