# @(#)interp	8.4 (Berkeley) 1/13/95
			Nvi Interpreter API

Introduction:
    The intention is to provide a way to graft a fairly generic extension
    language into nvi.  I think that the obvious candidates are Tcl/Rush,
    Scheme, Python and Perl5.  Since the interpretation language chosen
    is often a religious issue, the method should be as flexible as
    possible.  I don't expect to rewrite the editor in the interpreted
    language, so that isn't a consideration.

    Q: Is there any reason for nvi to support multiple interpreters in
       a single executable?

Interpreter functions in nvi:

 1: Function to get the current screen pointer.

    SCR *inter_screen();

	Return a pointer to the current screen.

 2: Functions to execute both ex and vi commands.  The return value of the
    function will be success/failure.  The editor itself will continue to
    handle the display of all messages and text for the foreseeable future.

    int inter_vicmd(SCR *, char *cmds, size_t len);
    int inter_excmd(SCR *, char *cmds, size_t len);

	The byte string cmds, of length len, is entered into the standard
	vi or ex parser, as if typed by the user.  The characters are not
	mapped in any way, i.e. the user's vi mappings don't apply.  If
	any error occurs, an error value is returned, and the rest of the
	characters are discarded.

 3: Functions to handle lines of text in the file.

    int inter_gline(SCR *, recno_t lno, char **lp, size_t *lenp);

	Return a pointer to the text of the line lno, into the location
	referenced by lp, and its length into the location referenced by
	lenp.

    int inter_dline(SCR *, recno_t lno);

	Delete the line lno from the file.

    int inter_aline(SCR *, recno_t lno, char *lp, size_t len);

	Append a line consisting of the len bytes of text referenced by
	lp to the line lno.

    int inter_iline(SCR *, recno_t lno, char *lp, size_t len);

	Insert a line consisting of the len bytes of text referenced by
	lp before the line lno.

    int inter_sline(SCR *, recno_t lno, char *lp, size_t len);

	Replace line lno with the len bytes of text referenced by lp.

    int inter_lline(SCR *, recno_t *lnop);

	Return the number of the last line in the file in the location
	referenced by lnop.

 4: Function to post an error message to the user.

    int inter_msgq(SCR *, enum msgtype, char *fmt, ...);

    Display the message for the user.  Valid message types are:

	M_BERR       Error: M_ERR if  verbose, else bell.
	M_ERR        Error: Display in inverse video.
	M_INFO        Info: Display in normal video.
	M_SYSERR     Error: M_ERR, using strerror(3) message.
	M_VINFO       Info: M_INFO if verbose, else ignore.

 5: Function to manipulate cut buffers.

    int inter_setbuf(SCR *, CHAR_T buffer);

	Create the specified buffer if it does not exist (the
	buffer will have no contents).

    int inter_getbuf(SCR *, CHAR_T buffer, TEXT **textp);

	Return a pointer to the specified buffer in the location
	referenced by textp.  (Since a pointer to the real item
	is being returned, it can be manipulated in any way the
	interpreter chooses.)

 6: Functions to manipulate marks.

    int inter_setmark(SCR *, CHAR_T name);

	Create the specified mark if it does not exist (the
	mark will have no contents).

    int inter_getmark(SCR *, CHAR_T name, MARK **markp);

	Return a pointer to the specified mark in the location
	referenced by markp.  (Since a pointer to the real item
	is being returned, it can be manipulated in any way the
	interpreter chooses.)

 7: Function to manipulate screens.

    SCR *inter_iscreen();

	Create a new screen, and return a pointer to it.

    int inter_escreen(SCR *);

	End a screen.

 8: Functions to get input from the user.

    int inter_getchar(CHAR_T *chp,
	enum maptype {NONE, INPUT, COMMAND} mapt);

	Return a character from the keyboard into the location referenced
	by chp.  Mapt can be set to INPUT, COMMAND or NONE, depending on
	what vi mappings should be applied to the character.

    int inter_getline(SCR *, char *prompt, CHAR_T **linep,
	size_t *lenp, enum maptype {NONE, INPUT, COMMAND} mapt);

	Return a pointer to a line entered by the user, and its length,
	into the locations linep and lenp.  A prompt may be specified
	by prompt, and mappings by mapt.

    int inter_freeline(CHAR_T *linep);

	Free the memory that was allocated by inter_getline();

 9: Function to retrieve and set the cursor.

    int inter_getcursor(SCR *, MARK *mark);

	Store the current cursor position in mark.

    int inter_setcursor(SCR *, MARK *mark);

	Set the current cursor position to mark.

10: Function to return a motion command from the user.

    int inter_getmotion(SCR *,
	MARK *start, MARK *end, enum movetype {LINE, CHAR} *mt);

	Nvi gets a motion command from the user and returns the starting
	and stopping points of the movement, reordered from the beginning
	to the end of the file.  The standard rules for line/character
	motions are applied, and returned to the interpreter through the
	mt argument.

11: Functions to return pathnames.

12: Functions to return edit options.

13: Nvi commands which will send text to the interpreter.

    Nvi will have a new ex command "inter", which will pipe the rest of
    the line up to the first unescaped <newline> to the interpreter, of
    the following form:
   
	:[address[,address]] inter [count] command

    The interface from the ex command to the interpreter is a function:

    int inter_ex(
	SCR *,				/* Current screen. */
	char *cmd;			/* The command. */
	size_t len;			/* The command length. */
	MARK *start,			/* Starting address for INTER_EX */
	MARK *end,			/* Ending address for INTER_EX */
	int count);			/* Count. */

    Nvi will have a new vi command "*<buffer>" which will pipe the contents
    of the named buffer to the interpreter, of the following form:

	[count]*<buffer>

    The interface from the vi command to the interpreter is a function:

    int inter_vi(
	SCR *,				/* Current screen. */
	CHAR_T buffer,			/* Buffer. */
	int count);			/* Count. */
