Is Scheme a functional programming language?

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Scheme is a functional programming language sharing many features with languages of the Lips family. Scheme was among the first languages to support functional programming. Parts of schema end in “!”, commonly called a bang.
So, what’s a functional programming language? These are languages that with a design to deal with symbolic computations as well as list processing applications. This language is based on mathematical functions and can be categorized into pure functional languages (functional paradigms only) and Impure Functional Languages (functional and imperative programming).
Functional programming in Scheme means trying to avoid programming side effects, i.e., there is not much changing of the variable values after assigning them. And these are the parts ending in a bang, hinting that you are on the wrong track unless you know what you are doing.
Scheme isn’t a purely functional programming language. Reason? It allows side effects but only discourages them. So it is not a computational analog of a mathematical function. Instead, everything appears as just an expression. A scheme program appears as a single long, complicated expression.
Scheme has a lexical scope, i.e., when the procedures are defined, the code will define how they behave rather than where they are called. While lexical scopes are shared among all programming languages, Scheme was among the first languages to consistently use Lexical. This gave rise to closures, which are widely implemented in a lot of interpreted languages.
Like other functional programming languages, the Scheme is very efficient. Users get the benefits of working with a bug-free environment, thanks to the lack of state support. Besides, there is efficient parallel programming due to the lack of mutable state. That implies that no state-changes issues are absent in Scheme. Therefore, it’s possible and easy to program functions to work parallel with the instructions.
And with the independent units that can run concurrently, the entire structure is efficient.

Is Scheme a functional programming language

Scheme programming language

Being a high-level programming language, Scheme is one of the easiest programming languages you can use. Besides being statistically scoped, Scheme is a tail-recursive language whose design has exceptionally simple and straightforward semantics and various ways to carry out expressions. 

Experts term it as a very expressive language because of the ease of reading its syntaxes, though not as effortless as those of Ruby. By now, you know that Scheme uses data structures such as strings, vectors, tuples, numeric parts, and characters. But it is its rich data set that makes it a versatile programming language. Any program written in Scheme is portable across multiple platforms.  

What’s Scheme language?

Though an easy language, the Scheme is not beginner-friendly. Its basic interpreter is DrRacket, formerly called PLT Scheme. Dissi other programming languages, Scheme has few syntaxes, making a distinct set called syntactic forms. 

As one of the foremost programming languages to include first-class procedures like lambda calculus, Scheme proved the practicality of block structure and static scope rules in a dynamically typed language. Keep in mind; Scheme was the first LISP language to:

  • differentiate procedures from symbols and lambda expressions
  • use one lexical environment for all the variables 
  • to evaluate the operator position of a procedure call similar to an operand position

So, Scheme relies wholly on the procedure calls to express iterations, and this emphasizes that tail-recursive procedure calls are typically go-to’s which pass arguments.

Scheme is prominent in writing text editing programs. Optimizing and analyzing app-based compilers, developing operating systems, writing drivers for graphic cards, etc. Scheme is useful in creating numerical applications and developing programs for calculating huge financial-based tasks in the commercial sphere. Its recent application is the development of virtual reality (VR). 

You can easily port all applications written in Scheme across different platforms on various architectures. Why? The machine dependencies are entirely hidden from programmers. 

Become au fait with Scheme in the grander scheme of things.  Click here.

Is Scheme purely functional?

Scheme allows side effects; as such, it isn’t a purely functional programming dialect. Side effects simply mean changing other attributes of the program that are not contained within the functions, such as using the I/O streams or changing the global variable values. 

A pure function’s return doesn’t have other dependencies or effects on the overall program as it is only based on its inputs. Ideally, pure functions are similar to mathematical functions in terms of concept – for a given input, any pure function must return only one possible value. 

However, it might behave like a mathematical function returning that same value for other inputs. Besides, its inputs solely determine the input and not any additional value stored in the global state. 

Take the examples below:

  1. Pure function, i.e., no side effects, always returns the same output for the same input.

def add_1(x):

    return x + 1

  1. Impure function, i.e., it always doesn’t return the same value for the same input because its output relies on the input value (x) and the internally computed random value. 

import random

def f(x):

    if random.randint(1, 2) == 1:

        return x + 1

    return x + 2

As earlier stated, side effects are signs of impure functions even if they return a similar value for similar input. In this case, it modifies the value of the global variable, as in the case below. 

y = 1

def f(x):

    global y

    y += 1

    return x + 1

A programmer with a purely functional programming language doesn’t consider evaluating programs because eager evaluation typically returns a similar result to a lazy review. 

The side effects in Scheme are what makes it to be categorized as an impure functional programming language. The simplest side effects involve input and output (I/O).

What is Scheme language used for?

Schema is a dialect for implementing other programming languages. Or, it’s you may use it as a friendly language for transformational programming. Simply put, you can use Scheme to create programs that write programs or creating programs that can be easily customized or extended.

Ideally, the Scheme has attractive features to implement many things, including scripting, constructing new languages, and carrying out application-specific programming environments.

Note that Scheme systems are interactive. As a result, they allow to create and test parts of programs incrementally. That makes it much similar to BASIC or Tcl, but it stands out for being a more expressive language and far cleaner. 

The impressive thing about Scheme is that it can be compiled. As such, you can create a program that runs faster. So, you can make programs that run faster, like the C programming language. Though not as quickly as a C language, Scheme cannot be far much slower when used with a good Scheme compiler. 

Typical applications of Scheme include:

  • Writing text editing programs
  • Analyzing and optimizing application based compilers
  • Writing drivers for graphics cards
  • Developing operating systems 
  • Developing numerically based applications
  • Writing programs to calculate large finance based tasks 
  • Development of VR (virtual reality)

The application of the Scheme goes far, much beyond this. Scheme differs from other interactive languages for its decent design. It’s just not just a collection of parts to fulfill programming needs. Instead, the program was designed as a general-purpose language from the outset, combining the top features of the earlier two languages. 

Simply put, Scheme is a radicle version of Lisp – it carries the best features of Algol and Lisp. The ability to port Scheme applications across various platforms on different architectures makes it a flexible programming program. Beyond that, you can compile scheme language to C using Gambit-C, free software made up of an interpreter and compiler. 

What is a functional programming language?

A functional language is a declarative programming paradigm that creates programs by application of sequential functions instead of statements. As such, the design of these programs is meant to operate symbolic computations as well as list process applications. Practically, its basis is mathematical functions. 

Click here if programming languages is your thing.

Each function in functional programming takes an input value and returns a consistent output value, i.e., the output is not affected by the program’s state. The entire function completes one operation, and you can compose them In a sequence to complete a complex procedure. 

The result of functional programming is a modular code – programmers can reuse practical program functions across the programs. Besides, it can be returned, called, and passed as a parameter. 

When solutions have little physical means and can be easily expressed in functions, that when you can, functional programming becomes a suitable tool. Unlike object-oriented programs that model the real world, practical programs are perfect for mathematical expressions and functions in which the end or intermediate values have no physical correlation. 

Types of functional programming:

  • Pure Functional − it supports functional paradigms only
  • Impure Functional − it supports the functional and imperative programming styles – for instance, LISP.

Functional Programming Features

  • The mathematical support functions – functional programming support mathematical functions using recursion and conditional expression to perform computations.
  • Its supports lazy evaluation qualities and high order functions 
  • Lacks support for flow Controls such as loop and conditional statements 
  • They support common concepts, including Abstraction, Inheritance, Encapsulation, and Polymorphism.

What are the advantages of using functional programming languages?

  • Easy debugging: few factors affect pure functions; therefore, it’s effortless to locate bugged sections. 
  • Bugs-Free Code: there are side effects in functional programs since it doesn’t support the state. That makes it easy to write error-free codes. 
  • Nested Function support 
  • Lazy Evaluation − supports Lazy Constructs such as Lazy Maps, Lazy Lists, etc.

Is Scheme a scripting language?

Scheme is a versatile language that packs many features often found in interpreted languages – for instance, first-class functions, closures, and advanced meta-programming. But still, you can easily compile the Scheme. 

Remember, the implementation of programming languages is by compilers or interpreters and, in some cases, a mix of both. All languages, to some extent, are a mix of both, and the difference between the two is almost an invisible line. 

An interpreter is a bit slow as it reads the program’s source text, analyses it, and then executes it as it moves. A lot of time is spent on analyzing the character strings to understand what they mean.

A compiler reads the source text of a program and then translates it into machine code. It’s the machine code that will execute the program as it runs. 

Typically, a compiler doesn’t analyze each expression whenever it encounters. Instead, they analyze once and then record actions, which an interpreter would take. Simply put, a compiler may work as an interpreter, i.e., it pretends to interpret a program, and it records what an interpreter would do. 

A scripting language/scripts is simply a series of commands, w can be executed without needing compilations. That means that a scripting language is interpreted. Keep in mind; not all programming languages are scripts, but all scripting languages are programming languages.

Scheme has both an interpreter and compiler. But its ability to support features primarily found in interpreted languages makes it a scripting language. However, the difference between interpreted languages and schemes is how Scheme presents the most complex operations as simpler expressions. This is reduced task implementation in Scheme and gives the programmers the ability to extend a language with similar features. 

Scheme built-in functions

As a variant of LISP, Scheme shares a lot with the Lisp programming language. It was Lisp’s first dialect, whose implementation required the use of tail call optimization. This placed placing a solid emphasis on recursive algorithms and functional programming. 

Scheme’s design philosophy is a minimalist one – it specifies a small standard core and provides robust tools to extend the language. Owing to its structure and versatility, Scheme has greater application in artificial intelligence. 

The standard features include:

  • Syntax – schemes syntax is based on S-expression, i.e., a parenthesized list in which the operands follow the operator just as in Lisp. For instance, the expression “4 plus 5 times 5” is written in Scheme as (+ 4 (* 5 5)).
  • The use Lambda keyword – Scheme utilizes the lambda to show anonymous functions. Again, this is similar to Lisp. For instance, two represent an unknown function adding up two numbers; you can write it as the statement below (lambda (x y) (+ x y)).
  • Lexical scope — unlike Lisp, Scheme is statistically scoped and not dynamically scoped. It is easy to identify variables within the Scheme just by looking at its source code for the program. A unit code binds all variables within Scheme. Ideally, within the nested group functions, inner functions have access to variables and other parent scope sources. 
  • Variables and procedures have a shared namespace – that means that the same primitives that operate on variables can operate on functions and processes. 
  • Hygienic macros — the macros within Scheme are hygienic. These macros offer much flexibility to the programmer allowing extended programs functionality without interfering with its native syntax. 
  • Delayed evaluation – delayed evaluation within Scheme allows the implementation of asynchronous programming techniques like promises and futures.
  • Can natively evaluate its code 
  • Can redefine its standard procedures and functions.

Scheme vs. Racket

Both Racket and Scheme are descendants of Lisp. So, the core ideas in Racket are similar to those in Lisp. The same applies to Scheme, but Scheme is the origin of Racket. 

Scheme has not much built into the language, which helps programmers view things like object-oriented programming as not magical. Instead, they view them as patterns for organizing code. Typically, every aspect within Scheme is constructed from a minute set of primitives composed intuitive and natural. 

Since Scheme doesn’t accord many aspects a special status, it keeps programmers in an open-minded state. The result of this is allowing programmers to sample out different programming languages and paradigms.

On the other hand, Racket has a big bang approach and is very similar to Clojure, meaning you will encounter many (). Compared to Scheme, Racket is much easier to learn as it doesn’t try to be a pure language but has almost anything that a programmer needs. For instance, you can easily insert pictures into your programming and if you want to develop programs, use the DrRacket function. Besides, it has a package manager, which allows you to add libraries to your programs. 

Both languages boast an easy pickup syntax. But this is commonly an opinion. All Lisp languages were built to write programs, and that means they have a small syntax. Racket features a smaller syntax called Student Racket that eases the entire process. Again, the syntax is suitable for functional programming just as in Scheme, though it looks different from the mainstream languages. 

The unique thing about Racket is that it allows carrying out imperative habits and still encourage functional programming. The syntax you use to define a function is almost similar to the function that describes a variable. Additionally, in Racket, you’ll find a set of built-in high-order functions. 

Scheme has almost the same qualities since they are both LISP languages. The limitation for both languages is that they limit the uses for real-world experience. 

Scheme atom function

In Scheme, a function can be defined as an object bound to a name through define just like other values. However, there is a slightly different but equivalent syntax for defining functions – lambda is specified implicitly for function definition. 

On the other hand, the modern consideration of an atom is an element that is not a cons-pair and is also not null. So, it includes Numbers, Booleans, Strings, Symbols, and Characters.

Several authors use the term atom to denote a datum, not a “cons” pair. However, modern practices may require that you invert that, test for the “cons” instead of the atoms. 

Anything containing other atoms, e.g., a vector, is not considered an atom. Besides, record types such as SRFI-4 vectors and u8vectors are close to strings; however, they still have numbers, conceptually, “atoms.” So, within the context of Scheme, it makes sense as it concerns itself with symbols, procedure objects, and lists only. 

The definition above makes it clear that an empty list is not an atom. People’s concept of atoms is not an essential thing in real life, but it is important in the academic sphere. Ideally, the atom concept is from the original LISP paper, which specified two data types – a cons pair or a symbol. 

Nil is an atom basically because it is a symbol. However, Scheme splits the boolean #f, the empty list ‘(), and the symbol nil. But you can use S as a means of differentiating between the two types of symbols as well as pair. Note that it has the same functions. If you are using a modern Scheme or CL code, using pair is better.

Pure Scheme has no assignment statements and doesn’t use iterative constructs such as FOR or WHILE loops. Function calls perform all actions.


Scheme is a general-purpose language that descended from Algol and Lisp. This programming language has excellent application in research, industrial applications, and computing education. While Scheme isn’t a beginner-friendly coding language, many users can understand its syntax even on the first day of use. 

The key to using Scheme is understanding its syntaxes, which you must practice heavily. That means you get tutorials or purchase books that present the concept in a clear, concise manner. Needless to say, beginners must start with understanding the basics and finally proceeding to the advanced concepts. 

The general outlook of Scheme is more of an opinion because different people will put it into other uses. For many people, Scheme is a language and not a program. Beyond that, it’s possible to run Scheme on multiple platforms. But that depends on the type of compiler or interpreter you are using. So, in some cases, Scheme may not run on multiple platforms effectively. 

The ability to run Scheme on various platforms makes it a more machine-independent language, even more than C. however, you’ll need to use the proper cross-platform implementations. The best implantations include Racket, chicken, guile, and gambit-c. Bigloo scheme compiles to JVM, which is machine-independent. 

The most significant advantage of using Scheme is its expressive powers and development speed. That means it is straightforward to express a concept within Scheme. You’ll realize that Scheme places together the code lines, making it easier for you to identify variables. 

Another advantage is its simple syntax, which makes it very easy to learn. Remember, Scheme is a functional programming language – giving it its advantages. 

There are some disadvantages too – for instance, Scheme cannot do low-level operations. Besides, it has a weak standard r5rs since it doesn’t encompass modules. Above all, a programmer has to stick with a chosen implementation.

Luis Gillman
Luis Gillman

Hi, I Am Luis Gillman CA (SA), ACMA
I am a Chartered Accountant (SA) and CIMA (SA) and author of Due Diligence: A strategic and Financial Approach.

The book was published by Lexis Nexis on 2001. In 2010, I wrote the second edition. Much of this website is derived from these two books.

In addition I have published an article entitled the Link Between Due Diligence and Valautions.

Disclaimer: Whilst every effort has been made to ensure that the information published on this website is accurate, the author and owners of this website take no responsibility  for any loss or damage suffered as a result of relience upon the information contained therein.  Furthermore the bulk of the information is derived from information in 2018 and use therefore is at your on risk. In addition you should consult professional advice if required.