Hi Kashyap,
> I am having some trouble following what's going on in the in the intern
> logic. It took me some time to realize that Intern[2] was essentially
> forming the node of a binary tree :)
Correct, at least in pil64 and miniPicoLisp (in pil32 and Ersatz it is a hash
table).
> What's the purpose of the tables - Ascii6 and Ascii7? I tried looking for a
> writeup on string/symbol implementation but couldn't find it.
This is only in miniPicoLisp. To save space, it packs text in six or seven bits
per character. This is specified in miniPicoLisp/doc/structures
ASCII-6/7 -> 96 characters:
xxxxx0 NUL sp ./<> a-z
xxxxxx1 !"#$%&'()*+,- 0-9 :;=?@ A-Z [\]^_`{|}~
As you see, the distinction is made on bit zero. Presumably often used
characters occupy only 6 bits.
> In the the intern function there is a isTxt if block - is a symbol ever not
> txt?
Yes. We must distinguish between a symbol (a structure composed of at least one
cell) and its name (a bit pattern, basically a number).
The name in miniPicoLisp can either be 'txt' if it is short (again, see
miniPicoLisp/doc/structures)
sym
|
V
+-----+-----+
| txt | val |
+-----+-----+
or of arbitrary size
sym
|
V
+-----+-----+
| | | val |
+--+--+-----+
| tail (only name, no properties)
V
+-----+-----+
| bin | | |
+-----+--+--+
|
V
+-----+-----+
| bin | | |
+-----+--+--+
|
V
+-----+-----+
| bin | num |
+-----+-----+
- Alex
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