Learning objective
First-class object: Know that a function is a first-class object in functional programming languages and in imperative programming languages that support such objects. This means that it can be an argument to another function as well as the result of a function call. First-class objects (or values) are objects which may: • appear in expressions • be assigned to a variable • be assigned as arguments • be returned in function calls. For example, integers, floating-point values, characters and strings are first class objects in many programming languages.
Read the explanation, check the common trap, then practise with flashcards and questions.
At a glance
0
Flashcards
0
Questions
Topic
Functional programming paradigm
Subtopic
First-class object
Aqa A Level Computer ScienceFundamentals of functional programming
Study support
Understand this objective
Quick explanation
First-class object: Know that a function is a first-class object in functional programming languages and in imperative programming languages that support such objects. This means that it can be an argument to another function as well as the result of a function call. First-class objects (or values) are objects which may: • appear in expressions • be assigned to a variable • be assigned as arguments • be returned in function calls. For example, integers, floating-point values, characters and strings are first class objects in many programming languages
- This point belongs to Functional programming paradigm, especially First-class object.
- You need to be able to first-class object: Know that a function is a first-class object in functional programming languages and in imperative programming languages that support such objects. This means that it can be an argument to another function as well as the result of a function call. First-class objects (or values) are objects which may: • appear in expressions • be assigned to a variable • be assigned as arguments • be returned in function calls. For example, integers, floating-point values, characters and strings are first class objects in many programming languages.
- Use the linked flashcards and practice questions to check recall, then practise applying the idea in an exam-style answer.
Why it matters
This objective helps connect First-class object to exam-style questions, flashcards, and revision notes for Functional programming paradigm.
Quick student answer
What does it mean for a function to be a first-class object?
Direct answer
It can be used as an argument to another function and returned by a function call
Key terms
- First-class object: An object that may appear in expressions, be assigned to a variable, be assigned as an argument, or be returned in a function call.
- First-class function: A function treated as a first-class object, so it can be passed as an argument to another function and returned as the result of a function call.
Common trap
Assuming first-class objects are only functions: Functions can be first-class objects, but the specification also gives integers, floating-point values, characters and strings as examples of first-class values in many programming languages.
Related questions
Try this as a practice card
Question 1 of 4
Choose an answer, get feedback, then move sideways through the set.
0 of 4 attempted
Flashcard prompts
Flip through the key recall cards
Flashcard 1 of 4
Press Space to flip, arrows to move
Revision tools
Choose how to practise
Flashcards0 linked cards
No objective-specific flashcards are cached for this page. Use the topic hub to revise the surrounding flashcards without triggering a frozen-subject DB fallback.Open topic hub
Practice Questions0 linked questions
No objective-specific practice questions are cached for this page. Use the topic question bank to practise nearby curriculum questions without weakening the egress guard.Open topic questions
Related learning objectives
- Function type: Know that a function, f, has a function type f: A → B (where the type is A → B, A is the argument type, and B is the result type). Know that A is called the domain and B is called the co-domain. Know that the domain and co-domain are always subsets of objects in some data type. Loosely speaking, a function is a rule that, for each element in some set A of inputs, assigns an output chosen from set B, but without necessarily using every member of B. For example, f: {a,b,c,…z} → {0,1,2,…,25} could use the rule that maps a to 0, b to 1, and so on, using all values which are members of set B. The domain is a set from which the function’s input values are chosen. The co-domain is a set from which the function’s output values are chosen. Not all of the co-domain’s members need to be outputs.
Function type
- Function application: Know that function application means a function applied to its arguments. The process of giving particular inputs to a function is called function application, for example add(3,4) represents the application of the function add to integer arguments 3 and 4. The type of the function is f: integer x integer → integer where integer x integer is the Cartesian product of the set integer with itself. Although we would say that function f takes two arguments, in fact it takes only one argument, which is a pair, for example (3,4).
Function application
- Partial function application: Know what is meant by partial function application for one, two and three argument functions and be able to use the notations shown opposite. The function add takes two integers as arguments and gives an integer as a result. Viewed as follows in the partial function application scheme: add: integer → (integer → integer) add 4 returns a function which when applied to another integer adds 4 to that integer. The brackets may be dropped so function add becomes add: integer → integer → integer The function add is now viewed as taking one argument after another and returning a result of data type integer. 92
Partial function application
- Composition of functions: Know what is meant by composition of functions. The operation functional composition combines two functions to get a new function. Given two functions f: A → B g: B → C function g ○ f, called the composition of g and f, is a function whose domain is A and co-domain is C. If the domain and co-domains of f and g are ℝ, and f(x) = (x + 2) and g(y) = y3. Then g ○ f = (x + 2)3 f is applied first and then g is applied to the result returned by f.
Composition of functions