When a stand-alone executable created by `raco exe` needs to load
modules that start with a `#lang` line, there have been various
obstacles to adding the right run-time support via `++lib`. The
`++lang` flag addresses those problems and makes it easy to indicate
that enough should be embedded to support loading modules with a
specified language.
There are problems in the way that various handlers interact for the
"lang/reader.rkt" versus `(submod "." reader)` search path that
converts a language name to a reader. To accomodate the search in a
standalone executable (that does not provide access to collections in
general), the module name resolver must refrain from raising an
exception for a non-existent submodule path that refers to a
non-existent collection.
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