Support where clauses for proc groups

core/odin/parser/parser.odin

@@ -2553,6 +2553,17 @@ parse_operand :: proc(p: ^Parser, lhs: bool) -> ^ast.Expr {
 			for p.curr_tok.kind != .Close_Brace &&
 			    p.curr_tok.kind != .EOF {
 				elem := parse_expr(p, false)
+
+				if p.curr_tok.kind == .Where {
+					tok_where := expect_token(p, .Where)
+					cond := parse_expr(p, false)
+
+					be := ast.new(ast.Binary_Expr, elem.pos, end_pos(p.prev_tok))
+					be.left  = elem
+					be.op    = tok_where
+					be.right = cond
+					elem = be
+				}
 				append(&args, elem)
 
 				allow_token(p, .Comma) or_break