The plt-r5rs executable runs an R5RS program from a file that is supplied on the command line. If no program file is provided as a command-line argument, then a read-eval-print loop is started.
Before starting a read-eval-print loop, an initialization file is loaded, if it exists. The file is the same as the file reported by (find-system-path 'init-file), but with the characters mzscheme in the filename replaced by pltr5rs. For example, under Unix, the file is "~/.pltr5rsrc".
By default, plt-r5rs departs from R5RS conformance in one crucial way: the names of pre-defined functions cannot be redefined at the top level. This restriction enables better run-time performance. Use the --no-prim command-line flag – before a file to load, if any – to obtain the standard behavior for primitive bindings (at the cost of performance).