fix(frontends/lean): fixes #830

src/frontends/lean/builtin_exprs.cpp

@@ -383,11 +383,11 @@ static expr parse_proof(parser & p, expr const & prop) {
         auto pos = p.pos();
         return parse_begin_end_core(p, pos, get_end_tk(), true);
     } else if (p.curr_is_token(get_by_tk())) {
-        // parse: 'by' tactic
         auto pos = p.pos();
-        p.next();
-        expr t = p.parse_tactic();
-        return p.mk_by(t, pos);
+        return parse_by(p, 0, nullptr, pos);
+    } else if (p.curr_is_token(get_by_plus_tk())) {
+        auto pos = p.pos();
+        return parse_by_plus(p, 0, nullptr, pos);
     } else if (p.curr_is_token(get_using_tk())) {
         // parse: 'using' locals* ',' proof
         auto using_pos = p.pos();

src/frontends/lean/tokens.cpp

@@ -81,6 +81,7 @@ static name const * g_using_tk = nullptr;
 static name const * g_then_tk = nullptr;
 static name const * g_else_tk = nullptr;
 static name const * g_by_tk = nullptr;
+static name const * g_by_plus_tk = nullptr;
 static name const * g_rewrite_tk = nullptr;
 static name const * g_proof_tk = nullptr;
 static name const * g_qed_tk = nullptr;
@@ -233,6 +234,7 @@ void initialize_tokens() {
     g_then_tk = new name{"then"};
     g_else_tk = new name{"else"};
     g_by_tk = new name{"by"};
+    g_by_plus_tk = new name{"by+"};
     g_rewrite_tk = new name{"rewrite"};
     g_proof_tk = new name{"proof"};
     g_qed_tk = new name{"qed"};
@@ -386,6 +388,7 @@ void finalize_tokens() {
     delete g_then_tk;
     delete g_else_tk;
     delete g_by_tk;
+    delete g_by_plus_tk;
     delete g_rewrite_tk;
     delete g_proof_tk;
     delete g_qed_tk;
@@ -538,6 +541,7 @@ name const & get_using_tk() { return *g_using_tk; }
 name const & get_then_tk() { return *g_then_tk; }
 name const & get_else_tk() { return *g_else_tk; }
 name const & get_by_tk() { return *g_by_tk; }
+name const & get_by_plus_tk() { return *g_by_plus_tk; }
 name const & get_rewrite_tk() { return *g_rewrite_tk; }
 name const & get_proof_tk() { return *g_proof_tk; }
 name const & get_qed_tk() { return *g_qed_tk; }

src/frontends/lean/tokens.h

@@ -83,6 +83,7 @@ name const & get_using_tk();
 name const & get_then_tk();
 name const & get_else_tk();
 name const & get_by_tk();
+name const & get_by_plus_tk();
 name const & get_rewrite_tk();
 name const & get_proof_tk();
 name const & get_qed_tk();

src/frontends/lean/tokens.txt

@@ -76,6 +76,7 @@ using        using
 then         then
 else         else
 by           by
+by_plus      by+
 rewrite      rewrite
 proof        proof
 qed          qed

tests/lean/run/830.lean

@@ -0,0 +1,30 @@
+variable P : Prop
+premise HP : P
+
+example : P :=
+have H : P, from HP,
+H
+
+example : P :=
+have H : P, from HP,
+show P, from H
+
+example : P :=
+have H : P, from HP,
+by+ exact H
+
+example : P :=
+have H : P, from HP,
+show P, by+ exact H
+
+example : P :=
+have H : P, from HP,
+show P, begin+ exact H end
+
+example : P :=
+have H : P, from HP,
+show P, using H, by exact H
+
+example : P :=
+assert H : P, from HP,
+show P, by exact H