fix(frontends/lean/parser): fix deadlock in macro parser

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

examples/lean/macros.lean

@@ -0,0 +1,94 @@
+(**
+ -- This example demonstrates how to create Macros for automating proof
+ -- construction using Lua.
+
+ -- This macro creates the syntax-sugar
+ --     name bindings ',' expr
+ -- For a function f with signature
+ --    f : ... (A : Type) ... (Pi x : A, ...)
+ --
+ -- farity is the arity of f
+ -- typepos is the position of (A : Type) argument
+ -- lambdapos is the position of the (Pi x : A, ...) argument
+ --
+ -- Example: suppose we invoke
+ --
+ --    binder_macro("for", Const("ForallIntro"), 3, 1, 3)
+ --
+ -- Then, the macro expression
+ --
+ --     for x y : Int, H x y
+ --
+ -- produces the expression
+ --
+ --     ForallIntro Int _ (fun x : Int, ForallIntro Int _ (fun y : Int, H x y))
+ --
+ -- The _ are placeholders (aka) holes that will be filled by the Lean
+ -- elaborator.
+ function binder_macro(name, f, farity, typepos, lambdapos)
+    macro(name, { macro_arg.Bindings, macro_arg.Comma, macro_arg.Expr },
+          function (bindings, body)
+             local r = body
+             for i = #bindings, 1, -1 do
+                local bname = bindings[i][1]
+                local btype = bindings[i][2]
+                local args  = {}
+                args[#args + 1] = f
+                for j = 1, farity, 1 do
+                   if j == typepos then
+                      args[#args + 1] = btype
+                   elseif j == lambdapos then
+                      args[#args + 1] = fun(bname, btype, r)
+                   else
+                      args[#args + 1] = mk_placeholder()
+                   end
+                end
+                r = mk_app(unpack(args))
+             end
+             return r
+    end)
+ end
+
+ function nary_macro(name, f, farity)
+    local bin_app = function(e1, e2)
+       local args = {}
+       args[#args + 1] = f
+       for i = 1, farity - 2, 1 do
+          args[#args + 1] = mk_placeholder()
+       end
+       args[#args + 1] = e1
+       args[#args + 1] = e2
+       return mk_app(unpack(args))
+    end
+
+    macro(name, { macro_arg.Expr, macro_arg.Expr, macro_arg.Exprs },
+          function (e1, e2, rest)
+             local r = bin_app(e1, e2)
+             for i = 1, #rest do
+                r = bin_app(r, rest[i])
+             end
+             return r
+    end)
+ end
+
+ binder_macro("for", Const("ForallIntro"), 3, 1, 3)
+ binder_macro("assume", Const("Discharge"), 3, 1, 3)
+ nary_macro("instantiate", Const("ForallElim"), 4)
+ nary_macro("mp", Const("MP"), 4)
+**)
+
+Definition Set (A : Type) : Type := A → Bool
+
+Definition element {A : Type} (x : A) (s : Set A) := s x
+Infix 60 ∈ : element
+
+Definition subset {A : Type} (s1 : Set A) (s2 : Set A) := ∀ x, x ∈ s1 ⇒ x ∈ s2
+Infix 50 ⊆ : subset
+
+Theorem SubsetTrans (A : Type) : ∀ s1 s2 s3 : Set A, s1 ⊆ s2 ⇒ s2 ⊆ s3 ⇒ s1 ⊆ s3 :=
+   for s1 s2 s3, assume (H1 : s1 ⊆ s2) (H2 : s2 ⊆ s3),
+      show s1 ⊆ s3,
+        for x, assume Hin : x ∈ s1,
+           show x ∈ s3,
+             let L1 : x ∈ s2 := mp (instantiate H1 x) Hin
+             in mp (instantiate H2 x) L1

src/frontends/lean/parser.cpp

@@ -280,6 +280,8 @@ class parser::imp {
     bool curr_is_lcurly() const { return curr() == scanner::token::LeftCurlyBracket; }
     /** \brief Return true iff the current token is a ':' */
     bool curr_is_colon() const { return curr() == scanner::token::Colon; }
+    /** \brief Return true iff the current token is a ',' */
+    bool curr_is_comma() const { return curr() == scanner::token::Comma; }
     /** \brief Return true iff the current token is a ':=' */
     bool curr_is_assign() const { return curr() == scanner::token::Assign; }
     /** \brief Return true iff the current token is an 'in' token */
@@ -856,86 +858,120 @@ class parser::imp {
         case scanner::token::CommandId:
         case scanner::token::Eof:
         case scanner::token::ScriptBlock:
+        case scanner::token::In:
             return false;
         default:
             return true;
         }
     }
 
+    typedef buffer<std::pair<macro_arg_kind, void*>> macro_arg_stack;
+
     /**
        \brief Parse a macro implemented in Lua
     */
-    expr parse_macro(lua_State * L, list<macro_arg_kind> const & args, unsigned num_args, pos_info const & p) {
-        if (args) {
-            auto k = head(args);
+    expr parse_macro(list<macro_arg_kind> const & arg_kinds, luaref const & proc, macro_arg_stack & args, pos_info const & p) {
+        if (arg_kinds) {
+            auto k = head(arg_kinds);
             switch (k) {
-            case macro_arg_kind::Expr:
-                push_expr(L, parse_expr());
-                return parse_macro(L, tail(args), num_args + 1, p);
+            case macro_arg_kind::Expr: {
+                expr e = parse_expr(g_app_precedence);
+                args.emplace_back(k, &e);
+                return parse_macro(tail(arg_kinds), proc, args, p);
+            }
             case macro_arg_kind::Exprs: {
-                lua_newtable(L);
-                int i = 1;
+                buffer<expr> exprs;
                 while (is_curr_begin_expr()) {
-                    push_expr(L, parse_expr(g_app_precedence));
-                    lua_rawseti(L, -2, i);
-                    i = i + 1;
+                    exprs.push_back(parse_expr(g_app_precedence));
                 }
-                return parse_macro(L, tail(args), num_args + 1, p);
+                args.emplace_back(k, &exprs);
+                return parse_macro(tail(arg_kinds), proc, args, p);
             }
             case macro_arg_kind::Bindings: {
                 mk_scope scope(*this);
                 bindings_buffer bindings;
                 parse_expr_bindings(bindings);
-                lua_newtable(L);
-                int i = 1;
-                for (auto const & b : bindings) {
-                    lua_newtable(L);
-                    push_name(L, std::get<1>(b));
-                    lua_rawseti(L, -2, 1);
-                    push_expr(L, std::get<2>(b));
-                    lua_rawseti(L, -2, 2);
-                    lua_rawseti(L, -2, i);
-                    i = i + 1;
-                }
-                return parse_macro(L, tail(args), num_args + 1, p);
+                args.emplace_back(k, &bindings);
+                return parse_macro(tail(arg_kinds), proc, args, p);
             }
             case macro_arg_kind::Comma:
                 check_comma_next("invalid macro, ',' expected");
-                return parse_macro(L, tail(args), num_args, p);
+                return parse_macro(tail(arg_kinds), proc, args, p);
             case macro_arg_kind::Assign:
                 check_comma_next("invalid macro, ':=' expected");
-                return parse_macro(L, tail(args), num_args, p);
-            case macro_arg_kind::Id:
-                push_name(L, curr_name());
-                next();
-                return parse_macro(L, tail(args), num_args + 1, p);
-            }
+                return parse_macro(tail(arg_kinds), proc, args, p);
+            case macro_arg_kind::Id: {
+                name n = curr_name();
+                args.emplace_back(k, &n);
+                return parse_macro(tail(arg_kinds), proc, args, p);
+            }}
             lean_unreachable();
         } else {
             // All arguments have been parsed, then call Lua procedure proc.
             m_last_script_pos = p;
-            pcall(L, num_args, 1, 0);
-            if (is_expr(L, -1)) {
-                expr r = to_expr(L, -1);
-                lua_pop(L, 1);
-                return save(r, p);
-            } else {
-                lua_pop(L, 1);
-                throw parser_error("failed to execute macro", p);
-            }
+            return m_script_state->apply([&](lua_State * L) {
+                    proc.push();
+                    for (auto p : args) {
+                        macro_arg_kind k = p.first;
+                        void * arg       = p.second;
+                        switch (k) {
+                        case macro_arg_kind::Expr:
+                            push_expr(L, *static_cast<expr*>(arg));
+                            break;
+                        case macro_arg_kind::Exprs: {
+                            auto const & exprs = *static_cast<buffer<expr>*>(arg);
+                            lua_newtable(L);
+                            int i = 1;
+                            for (auto e : exprs) {
+                                push_expr(L, e);
+                                lua_rawseti(L, -2, i);
+                                i = i + 1;
+                            }
+                            break;
+                        }
+                        case macro_arg_kind::Bindings: {
+                            bindings_buffer const & bindings = *static_cast<bindings_buffer*>(arg);
+                            lua_newtable(L);
+                            int i = 1;
+                            for (auto const & b : bindings) {
+                                lua_newtable(L);
+                                push_name(L, std::get<1>(b));
+                                lua_rawseti(L, -2, 1);
+                                push_expr(L, std::get<2>(b));
+                                lua_rawseti(L, -2, 2);
+                                lua_rawseti(L, -2, i);
+                                i = i + 1;
+                            }
+                            break;
+                        }
+                        case macro_arg_kind::Id:
+                            push_name(L, *static_cast<name*>(arg));
+                            break;
+                        default:
+                            lean_unreachable();
+                        }
+                    }
+                    pcall(L, args.size(), 1, 0);
+                    if (is_expr(L, -1)) {
+                        expr r = to_expr(L, -1);
+                        lua_pop(L, 1);
+                        return save(r, p);
+                    } else {
+                        lua_pop(L, 1);
+                        throw parser_error("failed to execute macro", p);
+                    }
+                });
         }
     }
 
     expr parse_macro(name const & id, pos_info const & p) {
         lean_assert(m_macros && m_macros->find(id) != m_macros->end());
         auto m = m_macros->find(id)->second;
-        list<macro_arg_kind> args = m.first;
-        luaref proc               = m.second;
-        return m_script_state->apply([&](lua_State * L) {
-                proc.push();
-                return parse_macro(L, args, 0, p);
-            });
-    }
+        list<macro_arg_kind> arg_kinds = m.first;
+        luaref proc                    = m.second;
+        macro_arg_stack args;
+        return parse_macro(arg_kinds, proc, args, p);
+            }
 
     /**
         \brief Parse an identifier that has a "null denotation" (See
@@ -1334,11 +1370,17 @@ class parser::imp {
         auto p = pos();
         next();
         expr t = parse_expr();
-        check_next(scanner::token::By, "invalid 'show _ by _' expression, 'by' expected");
-        tactic tac = parse_tactic_expr();
-        expr r = mk_placeholder(some_expr(t));
-        m_tactic_hints.insert(mk_pair(r, tac));
-        return save(r, p);
+        if (curr_is_comma()) {
+            next();
+            expr b = parse_expr();
+            return mk_let("H", t, b, Var(0));
+        } else {
+            check_next(scanner::token::By, "invalid 'show' expression, 'by' or ',' expected");
+            tactic tac = parse_tactic_expr();
+            expr r = mk_placeholder(some_expr(t));
+            m_tactic_hints.insert(mk_pair(r, tac));
+            return save(r, p);
+        }
     }
 
     /** \brief Parse <tt>'by' tactic</tt> */

src/library/placeholder.cpp

@@ -10,6 +10,7 @@ Author: Leonardo de Moura
 #include "kernel/replace_visitor.h"
 #include "library/expr_pair.h"
 #include "library/placeholder.h"
+#include "library/kernel_bindings.h"
 
 namespace lean {
 static name g_placeholder_name("_");
@@ -54,4 +55,16 @@ expr replace_placeholders_with_metavars(expr const & e, metavar_env const & menv
     replace_placeholders_with_metavars_proc proc(menv, new2old);
     return proc(e);
 }
+
+static int mk_placeholder(lua_State * L) {
+    if (lua_gettop(L) == 0) {
+        return push_expr(L, mk_placeholder());
+    } else {
+        return push_expr(L, mk_placeholder(some_expr(to_expr(L, 1))));
+    }
+}
+
+void open_placeholder(lua_State * L) {
+    SET_GLOBAL_FUN(mk_placeholder, "mk_placeholder");
+}
 }

src/library/placeholder.h

@@ -5,6 +5,7 @@ Released under Apache 2.0 license as described in the file LICENSE.
 Author: Leonardo de Moura
 */
 #pragma once
+#include "util/lua.h"
 #include "kernel/expr.h"
 #include "kernel/expr_maps.h"
 
@@ -33,4 +34,6 @@ bool has_placeholder(expr const & e);
    \c s, we store <tt>(*new2old)[t] = s</tt>.
 */
 expr replace_placeholders_with_metavars(expr const & e, metavar_env const & menv, expr_map<expr> * new2old = nullptr);
+
+void open_placeholder(lua_State * L);
 }

src/library/register_module.h

@@ -12,6 +12,7 @@ Author: Leonardo de Moura
 #include "library/hidden_defs.h"
 #include "library/substitution.h"
 #include "library/fo_unify.h"
+#include "library/placeholder.h"
 
 namespace lean {
 inline void open_core_module(lua_State * L) {
@@ -21,6 +22,7 @@ inline void open_core_module(lua_State * L) {
     open_hidden_defs(L);
     open_substitution(L);
     open_fo_unify(L);
+    open_placeholder(L);
 }
 inline void register_core_module() {
     script_state::register_module(open_core_module);