Chapter 11 The OCaml language

3 Names

Identifiers are used to give names to several classes of language objects and refer to these objects by name later:

These eleven name spaces are distinguished both by the context and by the capitalization of the identifier: whether the first letter of the identifier is in lowercase (written lowercase-ident below) or in uppercase (written capitalized-ident). Underscore is considered a lowercase letter for this purpose.

Naming objects

value-name::= lowercase-ident
operator-name::= prefix-symbol ∣ infix-op
infix-op::= infix-symbol
 * ∣ + ∣ - ∣ -. ∣ = ∣ != ∣ < ∣ > ∣ or ∣ || ∣ & ∣ && ∣ :=
 mod ∣ land ∣ lor ∣ lxor ∣ lsl ∣ lsr ∣ asr
constr-name::= capitalized-ident
tag-name::= capitalized-ident
typeconstr-name::= lowercase-ident
field-name::= lowercase-ident
module-name::= capitalized-ident
modtype-name::= ident
class-name::= lowercase-ident
inst-var-name::= lowercase-ident
method-name::= lowercase-ident

See also the following language extension: extended indexing operators.

As shown above, prefix and infix symbols as well as some keywords can be used as value names, provided they are written between parentheses. The capitalization rules are summarized in the table below.

Name spaceCase of first letter
Polymorphic variant tagsuppercase
Type constructorslowercase
Record fieldslowercase
Instance variableslowercase
Module typesany

Note on polymorphic variant tags: the current implementation accepts lowercase variant tags in addition to capitalized variant tags, but we suggest you avoid lowercase variant tags for portability and compatibility with future OCaml versions.

Referring to named objects

A named object can be referred to either by its name (following the usual static scoping rules for names) or by an access path prefix . name, where prefix designates a module and name is the name of an object defined in that module. The first component of the path, prefix, is either a simple module name or an access path name1 . name2 …, in case the defining module is itself nested inside other modules. For referring to type constructors, module types, or class types, the prefix can also contain simple functor applications (as in the syntactic class extended-module-path above) in case the defining module is the result of a functor application.

Label names, tag names, method names and instance variable names need not be qualified: the former three are global labels, while the latter are local to a class.