Not entirely, no.  For example, syntax-case and other macro systems can't be layered over syntax-rules.   By the same token, the Posix API (SRFI 170) can't be layered over R7RS-small.  It could be layered over an FFI, but there are just too many different kinds of FFIs out there. 

Here's the current list of non-portable SRFIs and pre-SRFIs that I have proposed to be voted on:

Conditions: ConditionsCowan

File I/O: FilesAdvancedCowan plus SettingsListsCowan

Threads: SRFI 18 plus optional SRFI 21 or FuturesCowan (simplified with monad)

Sockets: SRFI 106 or NetworkPortsCowan with NetworkEndpointsCowan

Datagram channels (UDP sockets): DatagramChannelsCowan

Timers: SRFI 120

Mutable environments: EnvironmentsMIT

Host environment (Posix): SRFI 170

Access to the REPL: ReplCowan

Library declarations: LibraryDeclarationsCowan

Interfaces: InterfacesCowan

Process control: ProcessesCowan

System commands: SystemCommandCowan

Pure delay/force: PureDelayedGloria

Delimited continuations: RacketGuileScheme48/KaliGaucheChicken

Continuation marks: SRFI 157

Extended exact numbers: SRFI 73 or ExtendedRationalsCowan

Adjustable strings: SRFI 118 (basic) or SRFI 140 (mutable/immutable)

Mutexes, condition variables: SRFI 18

Port type detector: see ticket #177

Internationalization of strings: GettextCowan

Chronometers: Chronometer

Character-cell terminals: TerminalsCowan

Graphics canvas: CanvasCowan


Comments are extremely welcome.

On Sat, Dec 21, 2019 at 7:24 PM Hendrik Boom <hendrik@topoi.pooq.com> wrote:
On Sat, Dec 21, 2019 at 11:02:55PM +0200, Lassi Kortela wrote:
>
> R6RS is quite a big language and there are already so many good
> implementations of it that new ones might not have much to add. Same
> situation as with Common Lisp. R7RS is such a small language that all kinds
> of niche implementations are interesting and useful to explore.

Which is why they split R7RS into a small language and a large language that
I home can be implemented entirely on top of the small langauge.

-- hendrik

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