feat(library/vm): add 'trace'

library/init/default.lean

@@ -8,7 +8,7 @@ import init.datatypes init.reserved_notation init.logic
 import init.relation init.nat init.prod
 import init.bool init.num init.sigma init.measurable init.setoid init.quot
 import init.funext init.function init.subtype init.classical init.simplifier
-import init.monad init.fin init.list init.char init.string init.to_string init.timeit
-import init.unsigned init.ordering
+import init.monad init.fin init.list init.char init.string init.to_string
+import init.timeit init.trace init.unsigned init.ordering
 import init.meta
 import init.wf init.wf_k

src/library/vm/vm_aux.cpp

@@ -7,18 +7,25 @@ Author: Leonardo de Moura
 #include <string>
 #include <iostream>
 #include "util/timeit.h"
+#include "library/trace.h"
 #include "library/vm/vm.h"
 #include "library/vm/vm_string.h"
 
 namespace lean {
 vm_obj vm_timeit(vm_obj const &, vm_obj const & s, vm_obj const & fn) {
     std::string msg = to_string(s);
-    timeit timer(std::cout, msg.c_str());
+    timeit timer(tout().get_stream(), msg.c_str());
+    return invoke(fn, mk_vm_unit());
+}
+
+vm_obj vm_trace(vm_obj const &, vm_obj const & s, vm_obj const & fn) {
+    tout() << to_string(s) << "\n";
     return invoke(fn, mk_vm_unit());
 }
 
 void initialize_vm_aux() {
     DECLARE_VM_BUILTIN("timeit", vm_timeit);
+    DECLARE_VM_BUILTIN("trace",  vm_trace);
 }
 
 void finalize_vm_aux() {

tests/lean/run/trace_tst.lean

@@ -0,0 +1,3 @@
+open nat
+
+vm_eval trace "step1" (λ u, trace "hello" (λ u, succ 3))