ML is a general-purpose functional programming language developed by Robin Milner and others in the late 1970s at the University of Edinburgh, whose syntax is inspired by ISWIM. Historically, ML stands for metalanguage as it was conceived to develop proof tactics in the LCF theorem prover (the language of which ML was the metalanguage is pplambda, a combination of the first-order predicate calculus and the simply-typed polymorphic lambda-calculus). It is known for its use of the Hindley-Milner type inference algorithm, which can infer the types of most values without requiring the extensive annotation often criticised in languages such as Java. Functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions. ... Robin Milner is a prominent British computer scientist. ... The University of Edinburgh, founded in 1583, is a renowned centre for teaching and research in Edinburgh, Scotland. ... ISWIM is a programming language devised by Peter J. Landin and first described in his article, The next 700 programming languages, published in the CACM in 1966. ... An interactive theorem prover developed at the universities of Edinburgh and Stanford by Robin Milner and others. ... First-order predicate calculus or first-order logic (FOL) permits the formulation of quantified statements such as there exists an x such that. ... In computer science, polymorphism means allowing a single definition to be used with different types of data (specifically, different classes of objects). ... In computer science, the lambda calculus is a formal system designed to investigate function definition, function application, and recursion. ... Type inference is a feature predominant in functional programming languages such as Haskell and ML or OCaml. ... Java is an object-oriented programming language developed by James Gosling and colleagues at Sun Microsystems in the early 1990s. ...

ML is often referred to as an impure functional language, because it permits side-effects, and therefore imperative programming, unlike purely functional programming languages such as Haskell. In computer science, a side-effect is a property of a programming language function that it modifies some state other than its return value. ... In computer science, imperative programming, as opposed to declarative programming, is a programming paradigm that describes computation in terms of a program state and statements that change the program state. ... Haskell logo Haskell is a standardized pure functional programming language with non-strict semantics named after the logician Haskell Curry. ...

Features of ML include a call-by-value evaluation strategy, first class functions, automatic memory management through garbage collection, parametric polymorphism, static typing, type inference, algebraic data types, pattern matching, and exception handling. An evaluation strategy (or reduction strategy) for a programming language is a set of (usually deterministic) rules for defining the evaluation of expressions under β-reduction. ... In computer science, a subroutine (function, procedure, or subprogram) is a sequence of code which performs a specific task, as part of a larger program, and is grouped as one, or more, statement blocks; such code is sometimes collected into software libraries. ... In computer science, garbage collection (also known as GC) is a form of automatic memory management. ... In computer science, polymorphism means allowing a single definition to be used with different types of data (specifically, different classes of objects). ... In computer science, a datatype or data type (often simply a type) is a name or label for a set of values and some operations which one can perform on that set of values. ... Type inference is a feature present in some strongly statically typed programming languages. ... In functional programming, new types can be defined, each of which has one or more constructors. ... Pattern matching is the act of checking for the presence of the constituents of a given pattern. ... Exception handling is a programming language construct or computer hardware mechanism designed to handle runtime errors or other problems (exceptions) which occur during the execution of a computer program. ...

Unlike Haskell, ML uses eager evaluation, which means that all subexpressions are always evaluated. One result of this is that you cannot use infinite lists per se. However, lazy evaluation and hence infinite lists can be simulated, through use of anonymous functions.

Today there are several languages in the ML family; the two major dialects are Standard ML and Caml, but others exist, including F# - an open research project that targets the Microsoft .NET platform. Ideas from ML have influenced numerous other languages, such as Haskell, Cyclone, and Nemerle. SML (Standard ML) is a general-purpose, modular, functional programming language with compile-time type checking and type inference. ... Objective Caml (OCaml) is a general-purpose programming language descended from the ML family, created by Xavier Leroy, Jérôme Vouillon, Damien Doligez, Didier Rémy and others in 1996. ... F# (pronounced F sharp) is a mixed functional and imperative programming language for the Microsoft . ... Haskell logo Haskell is a standardized pure functional programming language with non-strict semantics named after the logician Haskell Curry. ... The Cyclone programming language is intended to be a safe dialect of the C programming language. ... Nemerle logo Nemerle is a high-level statically-typed programming language for the . ...

ML's strengths are mostly applied in language design and manipulation (compilers, analyzers, theorem provers), but it is a general-purpose language also used in bioinformatics, financial systems, and applications including a genealogical database, a peer-to-peer client/server program, etc.

Examples of ML

Anatomy of a ML function

The "Hello World" of functional languages is the factorial function. Expressed as pure ML: To meet Wikipedias quality standards, this article or section may require cleanup. ... In mathematics, the factorial of a natural number n is the product of all positive integers less than and equal to n. ...

 fun fac : (fn: int -> int) 0 = 1 | fac n = n * fac (n-1); 

This describes the factorial as a recursive function, with a single terminating base case. It is similar to the descriptions of factorials found in mathematics textbooks. Much of ML code is similar to mathematics in facility and syntax.

The first line of the factorial function shown is optional, and describes the types of this function. It can be read as the function fac (fac) has type (:) function from integer to integer (fn: int -> int). That is, it takes an integer as an argument, and returns another integer. Rewritten without the unnecessary type annotation, it looks like:

 fun fac 0 = 1 | fac n = n * fac(n-1); 

The second line relies on pattern matching, an important part of ML programming. Note that parameters of a function are not in parentheses but separated by spaces. When the function's argument is 0 (zero) it will return the integer 1 (one). For all other cases the second line is tried. This is the recursion, and executes the function again until the base case is reached. Pattern matching is the act of checking for the presence of the constituents of a given pattern. ... A Sierpinski triangle —a confined recursion of triangles to form a geometric lattice. ...

External links

• Moscow ML, a popular implementation of Standard ML
• Standard ML of New Jersey, another popular implementation
• F#, an ML implementation using the Microsoft .NET framework
• MLton, a whole-program optimizing Standard ML compiler