ML, short for Meta Language, is a general-purpose functional programming language. It’s statically scoped, meaning that a variable always refers to its top-level environment. ML can be referred to as an impure functional language because it allows side effects, which most functional programming languages do not allow. A side effect is when a procedure changes a variable from outside its scope.
Like most programming languages, ML uses eager evaluation, so an expression is evaluated as soon as it’s bound to a variable. This is in direct opposition to lazy evaluation. However, lazy evaluation can still be achieved through the use of closures. ML is used for meta-programming, or writing programs that manipulate other programs. ML is known for its use of the Hindley-Milner type system, which automatically assigns the types of most expressions without requiring explicit type annotations and ensures type safety. ML is also used for:
- Scientific applications
- Theorem providers
- Analyzers, compilers, and programming languages
- Financial systems applications
- Bioinformatics and genealogical databases
Features of ML
ML is a strictly-typed language, meaning that a well-typed language will not cause runtime type errors. It features an automatic memory management system through garbage collection, so memory is automatically allocated and freed by the compiler. Parametric polymorphism is supported, meaning a single polymorphic function can be written to take a parameter of any compatible type. Other features include:
- First-class functions
- Static typing
- Type interference
- Pattern matching for functional arguments
- Exception handling
- Algebraic data types
ML is also the abbreviation for machine learning, a type of data analysis that uses algorithms to learn from data.