Stdlib

Unlike the steel builtins, some steel procedures are not written in rust and are instead written directly in scheme.

This means that these procedures cannot be required via (require-builtin <module name>), but have to be required via the normal require procedure, as in (require "<module name>").

Additionally, steel defines a so-called "prelude", a list of modules that steel loads into the context of the engine automatically. this list currently includes #%private/steel/stdlib, #%private/steel/control, #%private/steel/contract, #%private/steel/print, #%private/steel/ports, #%private/steel/reader, #%private/steel/match, #%private/steel/control and #%private/steel/contract.