Diagnose undefined functions in trace.

* share/txr/stdlib/trace.tl (sys:trace): If symbol-function
returns nil, throw exception.

* txr.1: Document the behavior, along with return values
of trace and untrace, and the tolerance of untrace to
bad arguments.

1 files changed, 23 insertions, 1 deletions

diff --git a/txr.1 b/txr.1
index 8b1b31eb..8e1d2dca 100644
--- a/txr.1
+++ b/txr.1
@@ -48586,11 +48586,19 @@ When
 is called with one or more arguments, it considers each
 argument to be the name of a global function. For each
 function, it turns on tracing, if it is not already turned on.
+If an argument denotes a nonexistent function, or is invalid
+function name syntax,
+.code trace
+terminates by throwing an exception, without processing the
+subsequent arguments, or undoing the effects already applied
+due to processing the previous arguments.
 
 When
 .code trace
 is called with no arguments, it lists the names of functions
-for which tracing is currently enabled.
+for which tracing is currently enabled. In other cases it
+returns
+.codn nil .
 
 When
 .code untrace
@@ -48603,6 +48611,13 @@ When
 is called with no arguments, it disables tracing for all
 functions.
 
+The
+.code untrace
+macro always returns
+.code nil
+and silently tolerates arguments which are not names of functions
+currently being traced.
+
 Tracing a function consists of printing a message prior to entry into the
 function indicating its name and arguments, and another message upon leaving
 the function indicating its return value, which is syntactically correlated
@@ -48638,6 +48653,13 @@ will not show the destructured internal macro arguments, but only the
 two arguments passed to the expander function: the whole form, and the
 environment.
 
+The
+.code trace
+and
+.code untrace
+functions return
+.codn nil .
+
 .SH* INTERACTIVE LISTENER
 
 .SS* Overview