New semantics for @(if) directive.

* eval.h (if_s): Declared.

* match.c (v_if): New static function.
(dir_tables_init): Register v_if in v_directive_table under if symbol.

* parser.y (IF): Token assigned to <lineno> type.
(if_clause, elif_clauses_opt, else_clause_opt): New syntactic
representation, understood by v_if.

* txr.1: Documented if semantics more precisely, dropped
the text about it being syntactic sugar for a cases with require,
added compatibility note.

1 files changed, 1 insertions, 1 deletions

diff --git a/eval.h b/eval.h
index d3e814ad..ae5008f1 100644
--- a/eval.h
+++ b/eval.h
@@ -26,7 +26,7 @@
 
 extern val dwim_s, lambda_s, vector_lit_s, vec_list_s, list_s;
 extern val hash_lit_s, hash_construct_s, struct_lit_s, qref_s;
-extern val eval_error_s;
+extern val eval_error_s, if_s;
 extern val eq_s, eql_s, equal_s;
 extern val last_form_evaled, last_form_expanded;