Hi
In the context of my "algorithm and data structures" course, I have recently
developed (in R6RS) an educational implementation of the following "stack" of
external algorithms&data structures:
- virtual disks : an implementation of "read-block" and "write-block"
on top of R6RS sequential files,
by positioning the current of a file to a given byte number and
reading/writing the number of bytes (in a byte vector) representing a disk block
- on top of this I have developed an educational file system by linking up
blocks
- in a freelist to allocate and deallocate blocks
- in a sequence to form a primitive educational directory
- I have implemented sequential files by linking up blocks
- read takes a scheme value, converts it to bytes and encodes the bytes
in the disk blocks
- write does the opposite
- I have implemented balanced multiway merge sort + polyphase sort on top of
these sequential files. The goal was to show students the number of block
transfers for external sorting.
- I have implemented SQL-styled data files as double linked lists of disk
blocks storing tuples + I have implemented B+-trees as index files. The trees
consist of nodes that are raw disk blocks of the first abstraction
- Finally, I have implemented a "mini SQL" that supports (create-table…)
(create-index…) (select/eq? …) (delete-where!…) (insert-into-table! …) using
these abstractions
I have written a draft of a textbook covering the implementation (in English).
It was my intention to publish it after a few iterations.
Now the questions:
My entire implementation-stack is based on:
(a) the ability to read and write a byte vector from/to a sequential
file/port in Scheme.
(b) the ability to position the current of a port to a given byte
number (and subsequently read/write a byte vector at that position).
(c) the ability to encode / decode integers, floats and strings in a
byte vector.
I had a look at the R7RS report.
- I cannot find (b)
- I understood that (c) has been removed to the big language.
Is (b) a conscious decision? Same question for (c) : to me, byte vectors are
pretty useless if you don't have a minimal amount of comfort for
encoding/decoding data types. And, given the fact that you no longer support
this comfort, is there sufficient support to break down/ build up Scheme data
types (integers, float,…) into / from raw bytes ? I.e., can I convert an
integer or a float to a byte vector? I only see string->utf8 and utf8->string.
However, converting a string to a byte vector is not the same as encoding a
string in an existing byte vector.
Regards
Wolf
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