export

(export symbols &optional package)

Makes symbols (a symbol or a list of them) external in package (the current package by default), so they are visible unqualified through a use-package and spell with one colon rather than two. Returns t. It is the runtime form of the defpackage :export clause; unexport is the inverse.

As in Common Lisp, a symbol has to be accessible in the package it is exported from: the package's own symbols always are, while a symbol homed in another package must have been imported or be inherited through the use list -- an inherited one becomes present (imported) as it is exported, so users of the package inherit the home's symbol. Two name conflicts signal too: a different symbol of that name already accessible in the package, and a package USING this one that already has its own symbol of that name present (not shadowing). Every such failure is a catchable package-error. unexport leaves the symbol present, just no longer external, and leaves an inherited symbol alone.

Packages are resolved at read/compile time here (see Packages), so a literal top-level call is consumed at compile time like in-package and takes effect for the forms that follow it — which is what makes it work on every backend. A runtime-computed call (a symbol list built at run time) works on the interpreter, and on every backend for a package the program created with make-package, whose member table records the export.

Exporting changes only accessibility, so it may come before or after the definitions it publishes — the everyday shape of a Common Lisp file, which defines its functions and exports them at the end, works:

A reference written before the export is still an error, as in Common Lisp — the symbol is not external yet at that point.

One deviation: a symbol exported after it was first named prints with the double colon (greeter3::hi), because the qualifier is part of the stored symbol here rather than recomputed at print time. Both spellings name the same symbol.