A strict programming language is a

programming language A programming language is a system of notation for writing computer programs. Programming languages are described in terms of their Syntax (programming languages), syntax (form) and semantics (computer science), semantics (meaning), usually def ...

that only allows strict functions (functions whose parameters must be evaluated completely before they may be called) to be defined by the user. A non-strict programming language allows the user to define non-strict functions, and hence may allow

lazy evaluation In programming language theory, lazy evaluation, or call-by-need, is an evaluation strategy which delays the evaluation of an Expression (computer science), expression until its value is needed (non-strict evaluation) and which avoids repeated eva ...

. In most non-strict languages, the non-strictness extends to data constructors.

Description

A strict programming language is a

which employs a strict

programming paradigm A programming paradigm is a relatively high-level way to conceptualize and structure the implementation of a computer program. A programming language can be classified as supporting one or more paradigms. Paradigms are separated along and descri ...

, allowing only strict functions (functions whose parameters must be evaluated completely before they may be called) to be defined by the user. A non-strict programming language allows the user to define non-strict functions, and hence may allow

. Non-strictness has several disadvantages which have prevented widespread adoption: * Because of the uncertainty regarding if and when expressions will be evaluated, non-strict languages generally must be purely functional to be useful. * All hardware architectures in common use are optimized for strict languages, so the best compilers for non-strict languages produce slower code than the best compilers for strict languages. * Space complexity of non-strict programs is difficult to understand and predict. * In many strict languages, some advantages of non-strict functions can be obtained through the use of macros or

thunk In computer programming Computer programming or coding is the composition of sequences of instructions, called computer program, programs, that computers can follow to perform tasks. It involves designing and implementing algorithms, step-by- ...

s. Strict programming languages are often associated with

eager evaluation In a programming language, an evaluation strategy is a set of rules for evaluating expressions. The term is often used to refer to the more specific notion of a ''parameter-passing strategy'' that defines the kind of value that is passed to the ...

, and non-strict languages with

, but other evaluation strategies are possible in each case. The terms "eager programming language" and "lazy programming language" are often used as synonyms for "strict programming language" and "non-strict programming language" respectively.

Examples

Nearly all

s in common use today are strict. Examples include C#,

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Perl Perl is a high-level, general-purpose, interpreted, dynamic programming language. Though Perl is not officially an acronym, there are various backronyms in use, including "Practical Extraction and Reporting Language". Perl was developed ...

(all versions, i.e. through version 5 and version 7), Python,

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Common Lisp Common Lisp (CL) is a dialect of the Lisp programming language, published in American National Standards Institute (ANSI) standard document ''ANSI INCITS 226-1994 (S2018)'' (formerly ''X3.226-1994 (R1999)''). The Common Lisp HyperSpec, a hyperli ...

, and ML. Some strict programming languages include features that mimic laziness. Raku (formerly known as Perl 6) has lazy lists, Python has generator functions, and Julia provides a macro system to build non-strict functions, as does Scheme. Examples for non-strict languages are

Haskell Haskell () is a general-purpose, statically typed, purely functional programming language with type inference and lazy evaluation. Designed for teaching, research, and industrial applications, Haskell pioneered several programming language ...

, R, Miranda, and Clean.

Extension

In most non-strict languages, the non-strictness extends to data constructors. This allows conceptually infinite data structures (such as the list of all

prime number A prime number (or a prime) is a natural number greater than 1 that is not a Product (mathematics), product of two smaller natural numbers. A natural number greater than 1 that is not prime is called a composite number. For example, 5 is prime ...

s) to be manipulated in the same way as ordinary finite data structures. It also allows for the use of very large but finite data structures such as the complete

game tree In the context of combinatorial game theory, a game tree is a graph representing all possible game states within a sequential game that has perfect information. Such games include chess, checkers, Go, and tic-tac-toe. A game tree can be us ...

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Citations

References

* * {{Refend Programming paradigms Evaluation strategy