feat(frontends/lean): add notation for then tactic

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>

src/frontends/lean/builtin_tactic_cmds.cpp

@@ -8,20 +8,42 @@ Author: Leonardo de Moura
 #include "frontends/lean/parser.h"
 
 namespace lean {
+static name g_comma(",");
+static name g_rbracket("]");
+
 tactic parse_fail_tactic(parser &) { return fail_tactic(); }
 tactic parse_id_tactic(parser &) { return id_tactic(); }
 tactic parse_assumption_tactic(parser &) { return assumption_tactic(); }
+tactic parse_echo_tactic(parser & p) {
+    if (!p.curr_is_string())
+        throw parser_error("invalid 'echo' tactic, string expected", p.pos());
+    tactic r = trace_tactic(p.get_str_val());
+    p.next();
+    return r;
+}
+tactic parse_tactic_seq(parser & p) {
+    tactic r = p.parse_tactic();
+    while (p.curr_is_token(g_comma)) {
+        p.next();
+        r = then(r, p.parse_tactic());
+    }
+    p.check_token_next(g_rbracket, "invalid tactic sequence, ']' expected");
+    return r;
+}
 
 void add_tactic(tactic_cmd_table & t, tactic_cmd_info && info) { t.insert(info.get_name(), info); }
 
 tactic_cmd_table get_builtin_tactic_cmds() {
     tactic_cmd_table t;
     add_tactic(t, tactic_cmd_info("fail", "always fail tactic", parse_fail_tactic));
+    add_tactic(t, tactic_cmd_info("echo", "trace tactic: display message", parse_echo_tactic));
     add_tactic(t, tactic_cmd_info("id", "do nothing tactic", parse_id_tactic));
     add_tactic(t, tactic_cmd_info("assumption", "solve goal if there is an assumption that is identical to the conclusion",
                                   parse_assumption_tactic));
     add_tactic(t, tactic_cmd_info("exact", "solve goal if there is an assumption that is identical to the conclusion",
                                   parse_assumption_tactic));
+    add_tactic(t, tactic_cmd_info("[", "tactic command sequence",
+                                  parse_tactic_seq));
     return t;
 }
 }

src/frontends/lean/parser.cpp

@@ -961,17 +961,23 @@ tactic parser::parse_tactic(unsigned /* rbp */) {
         auto r = parse_tactic();
         check_token_next(g_rparen, "invalid tactic, ')' expected");
         return r;
-    } else if (curr_is_identifier()) {
-        auto p  = pos();
-        name id = get_name_val();
-        next();
+    } else {
+        name id;
+        auto p = pos();
+        if (curr_is_identifier()) {
+            id = get_name_val();
+            next();
+        } else if (curr_is_keyword()) {
+            id = get_token_info().value();
+            next();
+        } else {
+            throw parser_error("invalid tactic, '(' or tactic command expected", p);
+        }
         if (auto it = tactic_cmds().find(id)) {
             return it->get_fn()(*this);
         } else {
-            throw parser_error(sstream() << "unknown tactic '" << id << "'", p);
+            throw parser_error(sstream() << "unknown tactic command '" << id << "'", p);
         }
-    } else {
-        throw parser_error("invalid tactic, '(' or tactic name expected", pos());
     }
 }
 

src/library/tactic/tactic.cpp

@@ -56,7 +56,7 @@ tactic now_tactic() {
         });
 }
 
-tactic cond(proof_state_pred const & p, tactic const & t1, tactic const & t2) {
+tactic cond(proof_state_pred p, tactic const & t1, tactic const & t2) {
     return tactic([=](environment const & env, io_state const & ios, proof_state const & s) -> proof_state_seq {
             return mk_proof_state_seq([=]() {
                     if (p(env, ios, s)) {

tests/lean/run/tactic2.lean

@@ -0,0 +1,4 @@
+import logic
+
+theorem tst {A B : Bool} (H1 : A) (H2 : B) : A
+:= by [echo "executing simple tactic", assumption]