The #lang at the start of a module file begins a shorthand for a
module form, much like ' is a shorthand for a quote form. Unlike
', the #lang shorthand does not work well in a REPL, in part
because it must be terminated by an end-of-file, but also
because the longhand expansion of #lang depends on the name of
the enclosing file. 6.2.1 The module Form The longhand form of a
module declaration, which works in a REPL as well as a file, is
(module name-id initial-module-path decl ...) where the name-id
is a name for the module, initial-module-path is an initial
import, and each decl is an import, export, definition, or
expression. In the case of a file, name-id must match the name
of the containing file, minus its directory path or file
extension. The initial-module-path is needed because even the
require form must be imported for further use in the module
body. In other words, the initial-module-path import bootstraps
the syntax available in the body. The most commonly used
initial-module-path is scheme, which