format: new precision - character for zero.

* stream.c (formatv): The - precision option character
produces a "sign" that is a zero. If this is used with leading
zeros, it will avoid generating a space. The requirements can
use improvement here, but one step at a time.

* tests/018/format.tl: Some tests.

* txr.1: Documented.

1 files changed, 3 insertions, 0 deletions

diff --git a/stream.c b/stream.c
index 248a51b2..77af0b37 100644
--- a/stream.c
+++ b/stream.c
@@ -3351,6 +3351,9 @@ val formatv(val stream_in, val fmtstr, struct args *al)
         case '+': case ' ':
           sign = ch;
           continue;
+        case '-':
+          sign = '0';
+          continue;
         case '*':
           saved_state = state;
           state = vf_star;