[PATCH]: Playing with rc: subshell functions.

[ori@eigenstate.org]

I don't know if I want this committed, but I figured
I'd toss it out if people care.

This patch adds support for running function bodies in
subshells, so

	fn foo @{...}

is sugar for for

	fn foo {@{ ... }}

This costs us something, though -- to fix a syntax ambiguity,
I removed the ability to name functions after keywords. So
before:

	fn if @ { echo wut }

would work, and you could do:

	term% 'if'
	wut
	term% '@'
	wut

Now, it'd be a syntax error:

	rc: #d/0: token if: syntax error

diff -r f1523de908ce sys/src/cmd/rc/syn.y
--- a/sys/src/cmd/rc/syn.y	Tue Dec 10 23:13:25 2019 -0800
+++ b/sys/src/cmd/rc/syn.y	Wed Dec 11 14:41:32 2019 -0800
@@ -17,7 +17,7 @@
 	struct tree *tree;
 };
 %type<tree> line paren brace body cmdsa cmdsan assign epilog redir
-%type<tree> cmd simple first word comword keyword words
+%type<tree> cmd simple first word comword keyword words comwords
 %type<tree> NOT FOR IN WHILE IF TWIDDLE BANG SUBSHELL SWITCH FN
 %type<tree> WORD REDIR DUP PIPE
 %%
@@ -68,8 +68,10 @@
 |	assign cmd %prec BANG	{$$=mung3($1, $1->child[0], $1->child[1], $2);}
 |	BANG cmd		{$$=mung1($1, $2);}
 |	SUBSHELL cmd		{$$=mung1($1, $2);}
-|	FN words brace		{$$=tree2(FN, $2, $3);}
-|	FN words		{$$=tree1(FN, $2);}
+|	FN comwords brace	{$$=tree2(FN, $2, $3);}
+|	FN comwords SUBSHELL brace
+				{$$=tree2(FN, $2, mung1($3, $4));}
+|	FN comwords		{$$=tree1(FN, $2);}
 simple:	first
 |	simple word		{$$=tree2(ARGLIST, $1, $2);}
 |	simple redir		{$$=tree2(ARGLIST, $1, $2);}
@@ -90,3 +92,5 @@
 keyword: FOR|IN|WHILE|IF|NOT|TWIDDLE|BANG|SUBSHELL|SWITCH|FN
 words:				{$$=(struct tree*)0;}
 |	words word		{$$=tree2(WORDS, $1, $2);}
+comwords:			{$$=(struct tree*)0;}
+|	comwords comword	{$$=tree2(WORDS, $1, $2);}