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Identifiers

Unison identifiers come in two flavors:

  1. Regular identifiers start with an alphabetic unicode character, emoji (which is any unicode character between 1F400 and 1FAFF inclusive), or underscore (''_''), followed by any number of alphanumeric characters, emoji, or the characters _, !, or \'. For example, foo, _bar4, qux', and set! are valid regular identifiers.
  2. Operators consist entirely of the characters !$%^&*-=+<>~\\/|:. For example, +, *, <>, and >>= are valid operators.

Namespace-qualified identifiers

The general reference for identifiers describes unqualified identifiers. An identifier can also be qualified. A qualified identifier consists of a qualifier or namespace, followed by a ., followed by either a regular identifier or an operator. The qualifier is one or more regular identifiers separated by . For example Foo.Bar.baz is a qualified identifier where Foo.Bar is the qualifier.

Absolutely qualified identifiers

Note that absolutely qualified identifiers are much less prevalent with the advent of Unison projects. They refer to a term from the root of the entire codebase, not the root of a particular project, so their usage is limited to legacy support of a pre-project era.

Namespace-qualified identifiers are relative to a ā€œcurrentā€ namespace, which the programmer can set (and defaults to the root of the current project). To ignore the current namespace, an identifier can have an absolute qualifier. An absolutely qualified name begins with a .. For example, the name .base.List always refers to the name .base.List, regardless of the current project or namespace, whereas the name base.List will refer to lib.base.List if the current namespace contains the base library in its lib namespace.

Hash-qualified identifiers

Any identifier, including a namespace-qualified one, can appear hash-qualified. A hash-qualified identifier has the form x#h where x is an identifier and #h is a hash literal. The hash disambiguates names that may refer to more than one thing.

Reserved words

The following names are reserved by Unison and cannot be used as identifiers: =, :, ->, ', do, |, !, `, if, then, else, forall, handle, unique, structural, where, use, &&, ||, true, false, type, ability, alias, let, namespace, cases, match, with, termLink, typeLink.