# AutoLISP

CADCraft runs AutoLISP routines (`.lsp` files). What is here and what is not yet:
[gaps.md](gaps.md) (E1).

## Loading and running

- **APPLOAD** (Tools > Load Application…, alias `AP`) opens a file browser filtered to `.lsp`
  files, starting in the folder the last one came from (kept in the preferences), and runs the
  chosen file. Cancelling the browser does nothing. A picked file loads as a typed name does, so a
  routine it starts that asks for a point waits for it. A desktop without a file browser asks for
  the name on the command line; the web has no file system, so it says to drop the `.lsp` file on
  the window and loads it from its contents. Only `.lsp` files are loaded; anything else is
  refused.
- **`(load "name")`** loads a file by path, with `.lsp` added when the name has none. A file
  APPLOAD loaded is found again by its name, also on the web where there is no file system.
- **`(defun c:NAME …)`** defines a command: type `NAME` at the command line. Built-in commands
  keep their names.
- **At the command line**, `(expression)` evaluates and shows the value, and `!variable` shows a
  variable. Typed at a command's prompt (not a free-text one), an expression's value answers it:
  `CIRCLE 0,0 (* 2 r)`.
- **Programmatically** (scripts, the control channel, MCP, the CLI): `lisp {code, inputs?}` and
  `appload {path} | {name, text | data}` run to the end and return `{value, output, error?}`.
  `appload` also returns `commands`, the `c:` commands the file defined, and a JSON call never
  opens a file dialog. `inputs` answer `get…` calls in order (numbers, strings, `[x, y]` points);
  a call with none left gets nil.

### At startup

CADCraft loads LISP from its **support folder**, `support` in the settings folder (on Windows
`%APPDATA%\CADCraft\support`, on macOS `~/Library/Application Support/CADCraft/support`, on
Linux `~/.config/cadcraft/support`; created at first start):

- `acad.lsp` once per session, into the first drawing; with `ACADLSPASDOC` set to 1, into every
  drawing;
- `acaddoc.lsp` into every drawing opened or created;
- then `S::STARTUP`, when they define it.

`(autoload "file" '("CMD1" "CMD2"))` in a startup file makes `CMD1` and `CMD2` commands that load
`file` (from the support folder too) the first time they are typed. Startup files run to the end
without asking for input. A drawing's own folder is never searched: an `acaddoc.lsp` that came
with a downloaded drawing does not run.

Each drawing has its own variables and functions. A routine is one undo step, whatever commands
it runs. A routine that waits for input (`getpoint`, `pause`) lets the window work meanwhile;
Esc stops it with "Function cancelled", which `*error*` receives. A long loop runs a slice per
frame, so the window stays live and Esc stops it too.

## The language

Integers are 32-bit and wrap as AutoLISP's do; any real makes arithmetic real. Variables are
dynamically scoped: a function's arguments and its locals (after `/`) are bound while it runs.
Symbols are case-insensitive. Reals print with six significant digits.

Nothing a routine does can crash the program: deep recursion is the error "internal stack limit
reached", malformed source is a reader error, and every built-in checks its arguments.

## Built-in functions

- **Forms:** `quote` `'` `function` `setq` `set` `if` `cond` `while` `repeat` `foreach` `progn`
  `and` `or` `defun` `defun-q` `lambda` `eval` `apply` `mapcar` `load` `autoload` `exit` `quit`
- **Numbers:** `+ - * / rem 1+ 1- abs min max sqrt exp log sin cos atan expt fix float gcd
  logand logior lsh ~ = /= < > <= >= zerop minusp numberp`
- **Lists:** `car cdr` and the `c…r` combinations up to four levels, `cons list append reverse
  length nth last member assoc subst acad_strlsort`, `vl-position vl-remove vl-sort
  vl-remove-if vl-remove-if-not vl-member-if vl-every vl-some vl-list-length vl-consp`
- **Predicates:** `atom listp null not type eq equal boundp vl-symbolp`
- **Strings:** `strcat strlen substr strcase itoa atoi atof chr ascii read wcmatch`,
  `vl-string-search vl-string-subst vl-string-trim vl-string-left-trim vl-string-right-trim
  vl-string-translate vl-string->list vl-list->string vl-prin1-to-string vl-princ-to-string
  vl-symbol-name vl-symbol-value vl-filename-base vl-filename-extension vl-filename-directory`
- **Geometry:** `polar distance angle inters trans` (`trans` returns the point: no UCS yet)
- **Output and files:** `princ prin1 print prompt terpri alert open close read-line write-line
  findfile`
- **Errors:** `*error*`, `vl-catch-all-apply vl-catch-all-error-p vl-catch-all-error-message`
- **Drawing:** `command` (also `command-s`, `vl-cmdf`) with `pause`, a command left open for the
  next call, and `(command)` to cancel; `getvar setvar`; `entget entmake entmod entdel entlast
  entnext entupd handent`; `ssget` (modes X, L, P, I, W, C, F, WP, CP, a point, or the user
  selecting; filters with wildcards and `-4` operators) `ssadd ssdel sslength ssname ssmemb
  sssetfirst ssgetfirst`; `tblsearch tblnext` (LAYER, LTYPE, STYLE, BLOCK, DIMSTYLE, APPID)
- **Input:** `initget getpoint getcorner getdist getangle getorient getreal getint getstring
  getkword entsel nentsel`
- **Units:** `rtos angtos distof angtof`
- **No-ops:** `vl-load-com gc redraw`; `ver`

Entity lists use the DXF group codes of CADCraft's DXF files: what `entget` returns is what a
DXF file holds for the object, plus `-1` (its name) and `410` (its layout). Angles (groups 50–58)
are in radians, as in AutoCAD, where the file holds degrees; `entmake`, `entmod` and `ssget`
filters take radians too.

`entmake` defines blocks: a BLOCK list (2 name, 70 flags, 10 base point, 4 description) begins a
definition, the entities made after it go into the block instead of the drawing, and an ENDBLK
list adds the block (redefining one of the same name) and returns its name. Flag 1 with a `*U`
name makes an anonymous block, named when it ends. A BLOCK while a definition is open, an
xref (flag 4), an invalid name, a block that inserts itself and a block being edited in place
(REFEDIT) return nil. A definition stays open across routines until ENDBLK, but a routine that
fails drops the one it began.

## Testing against the corpus

The AutoLISP conformance corpus (#648) lives in its own repository. Point `CADCRAFT_LISP_CORPUS`
at it and run `cargo test -p cadcraft-engine --test it lisp_corpus::`; without the variable the test
says it was skipped.