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6.12  Compilation units

unit-interface ::= { specification  [;;] }
unit-implementation ::= { definition  [;;] }

Compilation units bridge the module system and the separate compilation system. A compilation unit is composed of two parts: an interface and an implementation. The interface contains a sequence of specifications, just as the inside of a sigend signature expression. The implementation contains a sequence of definitions, just as the inside of a structend module expression. A compilation unit also has a name unit-name, derived from the names of the files containing the interface and the implementation (see chapter 8 for more details). A compilation unit behaves roughly as the module definition
module unit-name : sig  unit-interface end = struct  unit-implementation end

A compilation unit can refer to other compilation units by their names, as if they were regular modules. For instance, if U is a compilation unit that defines a type t, other compilation units can refer to that type under the name U.t; they can also refer to U as a whole structure. Except for names of other compilation units, a unit interface or unit implementation must not have any other free variables. In other terms, the type-checking and compilation of an interface or implementation proceeds in the initial environment
name1 : sig  interface1 end …  namen : sig  interfacen end
where name1 …  namen are the names of the other compilation units available in the search path (see chapter 8 for more details) and interface1 …  interfacen are their respective interfaces.
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