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# sanctuary forth (working title)
sanctuary forth is a 64-bit subroutine threaded forth system
for amd64 linux systems.
## stack effect notation
- `a`: memory address
- `c`: one byte value
- `n`: signed integer
- `u`: unsigned integer
- `?`: boolean flag
- `xt`: execution token
- `""`: string in input buffer
- `|`: 'or'
## Glossary
the following is a list of words available in this forth.
### `#tib ( -- a )`
variable containing the amount of characters in the input buffer.
### `>body ( xt -- a )`
yield the code field of xt.
### `>in ( -- a )`
variable containing the index of the first unparsed character
in the input buffer.
### `brk@ ( -- a )`
yields current program break.
### `bye ( -- )`
exits the forth system.
### `dp ( -- a )`
a variable that contains the lowest free byte of memory in user memory.
### `dp0 ( -- )`
a variable that contains the first byte of user memory.
### `dp$ ( -- )`
a variable that contains the last available byte of user memory.
### `executable ( a u -- )`
marks the u bytes starting at address a as executable.
this is used primarily to mark the program break,
which is used as the user memory space.
### `find ( a u -- a u 0 | xt -1 )`
look in the dictionary for the word a (of u characters).
a zero is returned along with the original given string
if no word was found. if a word was found,
its xt is returned along with the true flag.
### `grow ( u -- )`
grows the user memory space by u bytes.
### `here ( -- a )`
yields the address of the first available byte in user memory.
### `interpret ( -- )`
interprets the contents of the terminal input buffer
until it runs out.
### `latest ( -- a )`
a variable containing the execution token of
the most recently created word.
### `literal ( n -- ) IMMEDIATE COMPILE-ONLY`
compile a push of the literal value n into the currently compiling word.
### `number ( a u -- n 0 | -1 )`
convert given string into a number along with a flag.
if parsing a number fails then -1 (false) is returned
and no number is provided.
### `parse ( "name<c>" c -- a u )`
parse one word from the input buffer,
separated by a newline or the character c,
and return as a string.
### `parse-name ( "<ws>name<ws>" -- a u )`
parse one whitespace-separated word from the input buffer,
and return as a string.
tabs (ascii 0x09), newlines (ascii 0x10), and spaces (ascii 0x20)
are considered whitespace.
### `state ( -- a )`
a variable containing a boolean value.
if 0 (false), the system is in interpreting mode,
if -1 (true), the system is in compiling mode.
### `tib ( -- a )`
a variable containing the address of the current input buffer.
### `type ( a u -- )`
write u characters at a to output.
## dictionary format
note that the string length of one byte limits a word's name to 255 characters.
| field | size |
| :---- | :--- |
| link to previous word | 8 bytes |
| flag field | 1 byte |
| string length | 1 byte |
| string | <256 bytes |
| code | variable length |
## reserved registers
the register `r15` is reserved for the parameter stack pointer.
## differences from standard forth
for the most part this forth intends to be in line with standards
but it diverges in a few notable places:
- the most visally obvious one by far,
this forth uses lower case word names for core words.
- `find` takes `a u` instead of a counted string,
and does not return 1 for immediate words.
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