# 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

## Glossary

the following is a list of words available in this forth.

### `#tib   ( -- a )`
variable containing the amount of characters in the input buffer.

### `>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   ( u a -- )`
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.

### `grow   ( u -- )`
grows the user memory space by u bytes.

### `here   ( -- a )`
yields the address of the first available byte in user memory.

### `latest   ( -- a )`
a variable containing the execution token of
the most recently created word.

### `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.

## 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 registers `r14` and `r15` are reserved for the parameter stack
and the top of stack respectively.