support <:O>: if a label is not found, continue execution after the go-to statement

* this is a SciTECO extension - it's not in TECO-11
* Allows for select-case-like constructs with default-clauses as in
  :Os.^EQa$
    !* default *!
  !s.foo!
    !* ... *!
  !s.bar!
    !* ... *!
* Consistent with nOlabel0,label1,...$ if <n> is out of range.
  Unfortunately this form of computed goto is not applicable when
  "selecting" by strings or non-consecutive integers.
* In order to continue after the <:O> statement, we must keep the
  program counter along with the label we were looking for.
  At the end of the macro, the PC is restored instead of throwing
  an error.
* Since that would be very inefficient in loops - where potentially
  all iterations would result in rescanning till the end of the
  macro - we now store a completed-flag in the goto table.
  If it is set while trying to :O to an unknown label, we can
  just continue execution.

1 files changed, 7 insertions, 2 deletions

diff --git a/src/goto.h b/src/goto.h
index eda823f..05c7598 100644
--- a/src/goto.h
+++ b/src/goto.h
@@ -26,10 +26,14 @@
 typedef struct {
 	teco_rb3str_tree_t tree;
 
+	/** Whether to generate undo tokens (unnecessary in macro invocations) */
+	guint must_undo : 1;
+
 	/**
-	 * Whether to generate undo tokens (unnecessary in macro invocations)
+	 * Whether the table is guaranteed to be complete because the entire
+	 * macro has already been parsed.
 	 */
-	gboolean must_undo;
+	guint complete : 1;
 } teco_goto_table_t;
 
 /** @memberof teco_goto_table_t */
@@ -38,6 +42,7 @@ teco_goto_table_init(teco_goto_table_t *ctx, gboolean must_undo)
 {
 	rb3_reset_tree(&ctx->tree);
 	ctx->must_undo = must_undo;
+	ctx->complete = FALSE;
 }
 
 gboolean teco_goto_table_remove(teco_goto_table_t *ctx, const gchar *name, gsize len);