feat(frontends/lean): pp.beta is true by default

Remark: there is one exception (command: print definition). For this
command pp.beta is still false.

src/frontends/lean/builtin_cmds.cpp

@@ -191,9 +191,13 @@ environment print_cmd(parser & p) {
         name c = p.check_constant_next("invalid 'print definition', constant expected");
         environment const & env = p.env();
         declaration d = env.get(c);
+        io_state_stream out = p.regular_stream();
+        options opts        = out.get_options();
+        opts                = opts.update_if_undef(get_pp_beta_name(), false);
+        io_state_stream new_out = out.update_options(opts);
         if (!d.is_definition())
             throw parser_error(sstream() << "invalid 'print definition', '" << c << "' is not a definition", pos);
-        p.regular_stream() << d.get_value() << endl;
+        new_out << d.get_value() << endl;
     } else if (p.curr_is_token_or_id(get_instances_tk())) {
         p.next();
         name c = p.check_constant_next("invalid 'print instances', constant expected");

src/frontends/lean/pp.cpp

@@ -27,6 +27,7 @@ Author: Leonardo de Moura
 #include "library/abbreviation.h"
 #include "library/pp_options.h"
 #include "library/constants.h"
+#include "library/replace_visitor.h"
 #include "frontends/lean/pp.h"
 #include "frontends/lean/token_table.h"
 #include "frontends/lean/builtin_exprs.h"
@@ -1114,10 +1115,36 @@ pretty_fn::pretty_fn(environment const & env, options const & o):
     m_next_meta_idx = 1;
 }
 
+// Custom beta reduction procedure for the pretty printer.
+// We don't want to reduce application in show annotations.
+class pp_beta_reduce_fn : public replace_visitor {
+    virtual expr visit_meta(expr const & e) { return e; }
+    virtual expr visit_local(expr const & e) { return e; }
+
+    virtual expr visit_macro(expr const & e) {
+        if (is_show_annotation(e) && is_app(get_annotation_arg(e))) {
+            expr const & n = get_annotation_arg(e);
+            expr new_fn  = visit(app_fn(n));
+            expr new_arg = visit(app_arg(n));
+            return mk_show_annotation(mk_app(new_fn, new_arg));
+        } else {
+            return replace_visitor::visit_macro(e);
+        }
+    }
+
+    virtual expr visit_app(expr const & e) {
+        expr new_e = replace_visitor::visit_app(e);
+        if (is_head_beta(new_e))
+            return visit(head_beta_reduce(new_e));
+        else
+            return new_e;
+    }
+};
+
 format pretty_fn::operator()(expr const & e) {
     m_depth = 0; m_num_steps = 0;
     if (m_beta)
-        return pp_child(purify(beta_reduce(e)), 0).fmt();
+        return pp_child(purify(pp_beta_reduce_fn()(e)), 0).fmt();
     else
         return pp_child(purify(e), 0).fmt();
 }

src/library/pp_options.cpp

@@ -52,7 +52,7 @@ Author: Leonardo de Moura
 #endif
 
 #ifndef LEAN_DEFAULT_PP_BETA
-#define LEAN_DEFAULT_PP_BETA false
+#define LEAN_DEFAULT_PP_BETA true
 #endif
 
 #ifndef LEAN_DEFAULT_PP_NUMERALS
@@ -164,6 +164,7 @@ name const & get_pp_notation_option_name() { return *g_pp_notation; }
 name const & get_pp_metavar_args_name() { return *g_pp_metavar_args; }
 name const & get_pp_purify_metavars_name() { return *g_pp_purify_metavars; }
 name const & get_pp_purify_locals_name() { return *g_pp_purify_locals; }
+name const & get_pp_beta_name() { return *g_pp_beta; }
 
 unsigned get_pp_max_depth(options const & opts)       { return opts.get_unsigned(*g_pp_max_depth, LEAN_DEFAULT_PP_MAX_DEPTH); }
 unsigned get_pp_max_steps(options const & opts)       { return opts.get_unsigned(*g_pp_max_steps, LEAN_DEFAULT_PP_MAX_STEPS); }

src/library/pp_options.h

@@ -15,6 +15,7 @@ name const & get_pp_notation_option_name();
 name const & get_pp_metavar_args_name();
 name const & get_pp_purify_metavars_name();
 name const & get_pp_purify_locals_name();
+name const & get_pp_beta_name();
 
 unsigned get_pp_max_depth(options const & opts);
 unsigned get_pp_max_steps(options const & opts);

tests/lean/pp.lean

@@ -1,4 +1,4 @@
-prelude check λ {A : Type.{1}} (B : Type.{1}) (a : A) (b : B), a
+prelude set_option pp.beta false check λ {A : Type.{1}} (B : Type.{1}) (a : A) (b : B), a
 check λ {A : Type.{1}} {B : Type.{1}} (a : A) (b : B), a
 check λ (A : Type.{1}) {B : Type.{1}} (a : A) (b : B), a
 check λ (A : Type.{1}) (B : Type.{1}) (a : A) (b : B), a

tests/lean/pp_beta.lean

@@ -0,0 +1,7 @@
+open nat
+
+check (λ x : nat, x) 1
+
+set_option pp.beta false
+
+check (λ x : nat, x) 1

tests/lean/pp_beta.lean.expected.out

@@ -0,0 +1,2 @@
+1 : ℕ
+(λ (x : ℕ), x) 1 : ℕ