Back to index
LispMe Virtual File System
The Virtual File System (VFS) is a layer of software of the Palm API that
manages all installed file system libraries. It provides a unified API
to application developers while allowing them to seamlessly access
many different types of file systems -such as VFAT, HFS, and
NFS-on many different types of media, including Compact Flash,
Memory Stick, and SmartMedia.
All pathnames are absolute and must be provided in full. Relative
pathnames are not supported. All file systems support filenames
and labels that are up to 255 characters long. This support includes
any normal character including spaces and lower case characters in
any character set. It also includes the following special characters:
$ % ' - _ @ ~ ! ( ) ^ # & + , ; = [ ]
When the 8.3 naming convention is used to create a filename from a
long filename, the following guidelines are used.
When the 8.3 convention is used to create a volume label from a
long volume label the first eleven valid, non-space characters are
- The name is created from the first six valid, non-space
characters which appear before the last period. The only
valid characters are A-Z, 0-9, $, %, ', -, _, @, ~, ', !, (, ), ^, #, and
- The extension is the first three valid characters after the last
- The end of the six byte name is appended with a -1 for the
first occurrence of this file. Each subsequent occurrence uses
the next unique number.
The volume name is not considered part of the path name. Instead,
volumes are accessed by mount numbers, which are assigned by PalmOS
when inserting a card. In principle, several volumes can be mounted
at the same time, but I know of no device supporting more than one
card slot. The list of currently mounted volumes can be retrieved by
After ejecting and re-inserting the same memory card its volume
number will have changed (incremented)
So you should normally call (car (vfs-volumes)) to
retrieve the current (only?) mount number.
To access a file by name, both volume number and absolute path must
be specified. Should we change this and use a
more complex path including the volume label? The ancient AmigaDOS
did this and it worked quite well...
LispMe provides two layers to access VFS:
Low level file access
These calls are merely wrappers for the PalmOS VFS calls, which look
quite similar to C file calls, like fopen(), fread(),
etc. A file can be in read/write mode, you can access the attributes and
timestamps, and random access via
vfs-seek is possible.
However, data transfer is blockwise via LispMe strings.
Access via Scheme ports
On top of the low-level file calls LispMe provides a layer which
accesses VFS files as Scheme ports. All standard Scheme port functions
can be used. However, when using this layer a file can be either in
read or in write mode, not both.
Renaming and deleting files and creating directories works via
path names and is thus independent from the latter access modes.
Pickling and unpickling
When a session is pickled,
all open VFS files are closed and their opening parameters are
stored, as well as the current file position.
When the session is unpickled later, the files are
reopened using the parameters stored with the pickled data.
Thus, a running LispMe process can be interrupted (perhaps to
add some DateBook entries manually) and be continued afterward
Associated language elements