Unary + appends zero to lists.

Example:

  acid: +{}
  {0x00000000}

  acid: +{1}
  {0x00000001, 0x00000000}

  acid: defn x() { return {1} ; }
  acid: +x()
  {0x00000001, 0x00000000}

Cause:

  The parser converts '+x' to 'x+0'.  Such is reasonable for
  numeric arguments and has no effect on strings.  Unfortunately
  for lists, it results in a zero being appended.

This patch:

  The parser converts '+x' to 'x+ZN' and oadd() handles the ZN
  rhs when the expression is evaluated.

Patched:

  acid: +{}

  acid: +{1}
  {0x00000001}

  acid: defn x() { return {1} ; }
  acid: +x()
  {0x00000001}

Reference: /n/sources/patch/applied/acid.unary-plus-list-fix
Date: Tue Feb  6 17:20:47 CET 2007
Signed-off-by: philip.dye@cs.cmu.edu

--- /sys/src/cmd/acid/dbg.y	Tue Feb  6 17:20:41 2007
+++ /sys/src/cmd/acid/dbg.y	Tue Feb  6 17:29:36 2007
@@ -281,8 +281,7 @@
 		}
 		| '+' monexpr
 		{
-			$$ = con(0);
-			$$ = an(OADD, $2, $$);
+			$$ = an(OADD, $2, ZN);
 		}
 		| '-' monexpr
 		{
--- /sys/src/cmd/acid/expr.c	Tue Feb  6 17:20:44 2007
+++ /sys/src/cmd/acid/expr.c	Tue Feb  6 17:29:36 2007
@@ -202,12 +202,20 @@
 oappend(Node *n, Node *res)
 {
 	Node r, l;
+	int  empty ;
 
 	expr(n->left, &l);
 	expr(n->right, &r);
 	if(l.type != TLIST)
 		error("must append to list");
+	empty = ( l.l == nil && ( n->left->op == ONAME ) ) ;
 	append(res, &l, &r);
+	if ( empty ) {
+		Value * v = n->left->sym->v ;
+		v->type = res->type ;
+		v->Store = res->Store ;
+		v->comt = res->comt ;
+	}
 }
 
 void
@@ -325,7 +333,18 @@
 	Node l, r;
 
 	expr(n->left, &l);
-	expr(n->right, &r);
+	if ( n->right != ZN ) {
+	  expr(n->right, &r) ;
+	} else {
+		switch ( l.type ) {
+		default:
+			expr(con(0),&r) ;
+			break;
+		case TSTRING:
+		case TLIST:
+			break;
+		}
+	}
 	res->fmt = l.fmt;
 	res->op = OCONST;
 	res->type = TFLOAT;
@@ -358,6 +377,10 @@
 		}
 		break;
 	case TSTRING:
+		if ( n->right == ZN ) {
+			*res = l ;
+			break ;
+		}
 		if(r.type == TSTRING) {
 			res->type = TSTRING;
 			res->fmt = 's';
@@ -372,6 +395,10 @@
 		}
 		error("bad rhs for +");
 	case TLIST:
+		if ( n->right == ZN ) {
+			*res = l ;
+			break ;
+		}
 		res->type = TLIST;
 		switch(r.type) {
 		case TLIST: