New function: ignore, synonym of nilf.

This will be an official mechanism for indicating
deliberately unused variables.

* eval.c (eval_init): Register ignore intrinsic,
binding to the same function object as nilf.

* stdlib/compiler.tl (%const-foldable-funs%): Mention
ignore function, next to its nilf synonym.

* txr.1: Documented.

* stdlib/doc-syms.tl: Updated.

1 files changed, 22 insertions, 1 deletions

diff --git a/txr.1 b/txr.1
index 7be5a547..159c958d 100644
--- a/txr.1
+++ b/txr.1
@@ -58769,10 +58769,11 @@ with both optional arguments omitted:
   [iff a]  <--->  [iff a identity nilf]  <--->  a
 .brev
 
-.coNP Functions @ tf and @ nilf
+.coNP Functions @, tf @ nilf and @ ignore
 .synb
 .mets (tf << arg *)
 .mets (nilf << arg *)
+.mets (ignore << arg *)
 .syne
 .desc
 The
@@ -58789,6 +58790,11 @@ and the
 function returns
 .codn nil .
 
+The
+.code ignore
+function is a synonym of
+.codn nilf .
+
 Note: the following equivalences hold between these functions and the
 .code ret
 operator, and
@@ -58813,6 +58819,11 @@ and
   [mapcar (ret nil) list] <--> [mapcar nilf list]
 .brev
 
+Note: the
+.code ignore
+function can be used for suppressing unused variable
+warnings.
+
 .TP* Example:
 
 .verb
@@ -58851,6 +58862,16 @@ is even, then iff passes it into the
 function, which ignores the value and returns
 .codn nil .
 
+The following example shows how
+.code ignore
+may be used to suppress compiler warnings about unused parameters
+or other variables:
+
+.verb
+  (defun (x y)
+    (ignore x y))
+.brev
+
 .coNP Function @ retf
 .synb
 .mets (retf << value )