implement Shellbuiltin; include "sys.m";	sys: Sys;include "draw.m";include "sh.m";	sh: Sh;	Listnode, Context: import sh;	myself: Shellbuiltin;include "string.m";	str: String; initbuiltin(ctxt: ref Context, shmod: Sh): string{	sys = load Sys Sys->PATH;	sh = shmod;	myself = load Shellbuiltin "$self";	if (myself == nil)		ctxt.fail("bad module", sys->sprint("string: cannot load self: %r"));	str = load String String->PATH;	if (str == nil)		ctxt.fail("bad module",			sys->sprint("string: cannot load %s: %r", String->PATH));	ctxt.addbuiltin("prefix", myself);	ctxt.addbuiltin("in", myself);	names := array[] of {	"splitl", "splitr", "drop", "take", "splitstrl", "splitstrr",	"tolower", "toupper", "len", "alen", "slice", "fields",	"padl", "padr",	};	for (i := 0; i < len names; i++)		ctxt.addsbuiltin(names[i], myself);	return nil;} whatis(nil: ref Sh->Context, nil: Sh, nil: string, nil: int): string{	return nil;} getself(): Shellbuiltin{	return myself;} runbuiltin(ctxt: ref Context, nil: Sh,			argv: list of ref Listnode, nil: int): string{	case (hd argv).word {	"prefix" =>		(a, b) := earg2("prefix", ctxt, argv);		if (!str->prefix(a, b))			return "false";	"in" =>		(a, b) := earg2("in", ctxt, argv);		if (a == nil || !str->in(a[0], b))			return "false";	}	return nil;} runsbuiltin(ctxt: ref Context, nil: Sh,			argv: list of ref Listnode): list of ref Listnode{	name := (hd argv).word;	case name {	"splitl" =>		(a, b) := earg2("splitl", ctxt, argv);		return mk2(str->splitl(a, b));	"splitr" =>		(a, b) := earg2("splitr", ctxt, argv);		return mk2(str->splitr(a, b));	"drop" =>		(a, b) := earg2("drop", ctxt, argv);		return mk1(str->drop(a, b));	"take" =>		(a, b) := earg2("take", ctxt, argv);		return mk1(str->take(a, b));	"splitstrl" =>		(a, b) := earg2("splitstrl", ctxt, argv);		return mk2(str->splitstrl(a, b));	"splitstrr" =>		(a, b) := earg2("splitstrr", ctxt, argv);		return mk2(str->splitstrr(a, b));	"tolower" =>		return mk1(str->tolower(earg1("tolower", ctxt, argv)));	"toupper" =>		return mk1(str->toupper(earg1("tolower", ctxt, argv)));	"len" =>		return mk1(string len earg1("len", ctxt, argv));	"alen" =>		return mk1(string len array of byte earg1("alen", ctxt, argv));	"slice" =>		return sbuiltin_slice(ctxt, argv);	"fields" =>		return sbuiltin_fields(ctxt, argv);	"padl" =>		return sbuiltin_pad(ctxt, argv, -1);	"padr" =>		return sbuiltin_pad(ctxt, argv, 1);	}	return nil;} sbuiltin_pad(ctxt: ref Context, argv: list of ref Listnode, dir: int): list of ref Listnode{	if (tl argv == nil || !isnum((hd tl argv).word))		ctxt.fail("usage", "usage: " + (hd argv).word + " n [arg...]"); 	argv = tl argv;	n := int (hd argv).word * dir;	s := "";	for (argv = tl argv; argv != nil; argv = tl argv) {		s += word(hd argv);		if (tl argv != nil)			s[len s] = ' ';	}	if (n != 0)		s =  sys->sprint("%*s", n, s);	return ref Listnode(nil, s) :: nil;} sbuiltin_fields(ctxt: ref Context, argv: list of ref Listnode): list of ref Listnode{	argv = tl argv;	if (len argv != 2)		ctxt.fail("usage", "usage: fields cl s");	cl := word(hd argv);	s := word(hd tl argv); 	r: list of string; 	n := 0;	for (i := 0; i < len s; i++) {		if (str->in(s[i], cl)) {			r = s[n:i] :: r;			n = i + 1;		}	}	r = s[n:i] :: r;	rl: list of ref Listnode;	for (; r != nil; r = tl r)		rl = ref Listnode(nil, hd r) :: rl;	return rl;}  sbuiltin_slice(ctxt: ref Context, argv: list of ref Listnode): list of ref Listnode{	argv = tl argv;	if (len argv != 3 || !isnum((hd argv).word) ||			(hd tl argv).word != "end" && !isnum((hd tl argv).word))		ctxt.fail("usage", "usage: slice start end arg");	n1 := int (hd argv).word;	n2: int;	s := word(hd tl tl argv);	r := "";	if ((hd tl argv).word == "end")		n2 = len s;	else		n2 = int (hd tl argv).word;	if (n2 > len s)		n2 = len s;	if (n1 > len s)		n1 = len s;	if (n2 > n1)		r = s[n1:n2];	return mk1(r);} earg2(cmd: string, ctxt: ref Context, argv: list of ref Listnode): (string, string){	argv = tl argv;	if (len argv != 2)		ctxt.fail("usage", "usage: " + cmd + " arg1 arg2");	return (word(hd argv), word(hd tl argv));} earg1(cmd: string, ctxt: ref Context, argv: list of ref Listnode): string{	if (len argv != 2)		ctxt.fail("usage", "usage: " + cmd + " arg");	return word(hd tl argv);} mk2(x: (string, string)): list of ref Listnode{	(a, b) := x;	return ref Listnode(nil, a) :: ref Listnode(nil, b) :: nil;} mk1(x: string): list of ref Listnode{	return ref Listnode(nil, x) :: nil;} isnum(s: string): int{	for (i := 0; i < len s; i++)		if (s[i] > '9' || s[i] < '0')			return 0;	return 1;} word(n: ref Listnode): string{	if (n.word != nil)		return n.word;	if (n.cmd != nil)		n.word = sh->cmd2string(n.cmd);	return n.word;}