From 20a67e47caefc3caf1d4fef9612c5caf6a4fe611 Mon Sep 17 00:00:00 2001
From: Nikolaj Bjorner <nbjorner@microsoft.com>
Date: Sat, 22 May 2021 13:12:49 -0700
Subject: [PATCH] remove symbol -> zstring -> symbol round-trips

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
---
 src/ast/ast.cpp                   |  7 +++++++
 src/ast/ast.h                     | 11 ++++++++++-
 src/ast/rewriter/seq_axioms.cpp   |  2 +-
 src/ast/rewriter/seq_rewriter.cpp |  8 ++++----
 src/ast/seq_decl_plugin.cpp       | 16 ++++------------
 src/ast/seq_decl_plugin.h         | 13 +++----------
 src/model/seq_factory.h           | 14 ++++++++------
 src/parsers/smt2/smt2parser.cpp   |  2 +-
 src/smt/theory_str.cpp            |  3 +--
 src/smt/theory_str.h              | 11 ++++++-----
 src/smt/theory_str_mc.cpp         | 20 ++++++++------------
 src/util/zstring.cpp              | 14 +++++++++-----
 src/util/zstring.h                |  9 ++++++---
 13 files changed, 68 insertions(+), 62 deletions(-)

diff --git a/src/ast/ast.cpp b/src/ast/ast.cpp
index 96744bc9bc2..82f0d0c86f1 100644
--- a/src/ast/ast.cpp
+++ b/src/ast/ast.cpp
@@ -41,6 +41,9 @@ parameter::~parameter() {
     if (m_kind == PARAM_RATIONAL) {
         dealloc(m_rational);
     }
+    if (m_kind == PARAM_ZSTRING) {
+        dealloc(m_zstring);
+    }
 }
 
 parameter::parameter(parameter const& other) {
@@ -64,6 +67,7 @@ parameter& parameter::operator=(parameter const& other) {
     case PARAM_RATIONAL: m_rational = alloc(rational, other.get_rational()); break;
     case PARAM_DOUBLE: m_dval = other.m_dval; break;
     case PARAM_EXTERNAL: m_ext_id = other.m_ext_id; break;
+    case PARAM_ZSTRING: m_zstring = alloc(zstring, other.get_zstring()); break;
     default:
         UNREACHABLE();
         break;
@@ -99,6 +103,7 @@ bool parameter::operator==(parameter const & p) const {
     case PARAM_RATIONAL: return get_rational() == p.get_rational();
     case PARAM_DOUBLE: return m_dval == p.m_dval;
     case PARAM_EXTERNAL: return m_ext_id == p.m_ext_id;
+    case PARAM_ZSTRING: return get_zstring() == p.get_zstring();
     default: UNREACHABLE(); return false;
     }
 }
@@ -111,6 +116,7 @@ unsigned parameter::hash() const {
     case PARAM_SYMBOL:   b = get_symbol().hash(); break;
     case PARAM_RATIONAL: b = get_rational().hash(); break;
     case PARAM_DOUBLE:   b = static_cast<unsigned>(m_dval); break;
+    case PARAM_ZSTRING:  b = get_zstring().hash(); break;
     case PARAM_EXTERNAL: b = m_ext_id; break;
     }
     return (b << 2) | m_kind;
@@ -124,6 +130,7 @@ std::ostream& parameter::display(std::ostream& out) const {
     case PARAM_AST:      return out << "#" << get_ast()->get_id();
     case PARAM_DOUBLE:   return out << m_dval;
     case PARAM_EXTERNAL: return out << "@" << m_ext_id;
+    case PARAM_ZSTRING:  return out << get_zstring();
     default:
         UNREACHABLE();
         return out << "[invalid parameter]";
diff --git a/src/ast/ast.h b/src/ast/ast.h
index 70e079605f7..cdf53d4b280 100644
--- a/src/ast/ast.h
+++ b/src/ast/ast.h
@@ -22,6 +22,7 @@ Revision History:
 #include "util/vector.h"
 #include "util/hashtable.h"
 #include "util/buffer.h"
+#include "util/zstring.h"
 #include "util/symbol.h"
 #include "util/rational.h"
 #include "util/hash.h"
@@ -100,6 +101,7 @@ class parameter {
         PARAM_INT,
         PARAM_AST,
         PARAM_SYMBOL,
+        PARAM_ZSTRING,
         PARAM_RATIONAL,
         PARAM_DOUBLE,
         // PARAM_EXTERNAL is used for handling decl_plugin specific parameters.
@@ -119,6 +121,7 @@ class parameter {
         ast*         m_ast;     // for PARAM_AST
         symbol       m_symbol;  // for PARAM_SYMBOL
         rational*    m_rational; // for PARAM_RATIONAL
+        zstring*     m_zstring;  // for PARAM_ZSTRING
         double       m_dval;   // for PARAM_DOUBLE (remark: this is not used in float_decl_plugin)
         unsigned     m_ext_id; // for PARAM_EXTERNAL
     };
@@ -131,7 +134,9 @@ class parameter {
     explicit parameter(ast * p): m_kind(PARAM_AST), m_ast(p) {}
     explicit parameter(symbol const & s): m_kind(PARAM_SYMBOL), m_symbol(s) {}
     explicit parameter(rational const & r): m_kind(PARAM_RATIONAL), m_rational(alloc(rational, r)) {}
-    explicit parameter(rational && r) : m_kind(PARAM_RATIONAL), m_rational(alloc(rational, std::move(r))) {}
+    explicit parameter(rational && r) : m_kind(PARAM_RATIONAL), m_rational(alloc(rational, std::move(r))) {} 
+    explicit parameter(zstring const& s): m_kind(PARAM_ZSTRING), m_zstring(alloc(zstring, s)) {}
+    explicit parameter(zstring && s): m_kind(PARAM_ZSTRING), m_zstring(alloc(zstring, std::move(s))) {}
     explicit parameter(double d):m_kind(PARAM_DOUBLE), m_dval(d) {}
     explicit parameter(const char *s):m_kind(PARAM_SYMBOL), m_symbol(symbol(s)) {}
     explicit parameter(const std::string &s):m_kind(PARAM_SYMBOL), m_symbol(symbol(s)) {}
@@ -146,6 +151,7 @@ class parameter {
         case PARAM_RATIONAL: m_rational = nullptr; std::swap(m_rational, other.m_rational); break;
         case PARAM_DOUBLE: m_dval = other.m_dval; break;
         case PARAM_EXTERNAL: m_ext_id = other.m_ext_id; break;
+        case PARAM_ZSTRING: m_zstring = other.m_zstring; break;
         default:
             UNREACHABLE();
             break;
@@ -163,6 +169,7 @@ class parameter {
     bool is_rational() const { return m_kind == PARAM_RATIONAL; }
     bool is_double() const { return m_kind == PARAM_DOUBLE; }
     bool is_external() const { return m_kind == PARAM_EXTERNAL; }
+    bool is_zstring() const { return m_kind == PARAM_ZSTRING; }
 
     bool is_int(int & i) const { return is_int() && (i = get_int(), true); }
     bool is_ast(ast * & a) const { return is_ast() && (a = get_ast(), true); }
@@ -170,6 +177,7 @@ class parameter {
     bool is_rational(rational & r) const { return is_rational() && (r = get_rational(), true); }
     bool is_double(double & d) const { return is_double() && (d = get_double(), true); }
     bool is_external(unsigned & id) const { return is_external() && (id = get_ext_id(), true); }
+    bool is_zstring(zstring& s) const { return is_zstring() && (s = get_zstring(), true); }
 
     /**
        \brief This method is invoked when the parameter is
@@ -187,6 +195,7 @@ class parameter {
     ast * get_ast() const { SASSERT(is_ast()); return m_ast; }
     symbol get_symbol() const { SASSERT(is_symbol()); return m_symbol; }
     rational const & get_rational() const { SASSERT(is_rational()); return *m_rational; }
+    zstring const& get_zstring() const { SASSERT(is_zstring()); return *m_zstring; }
     double get_double() const { SASSERT(is_double()); return m_dval; }
     unsigned get_ext_id() const { SASSERT(is_external()); return m_ext_id; }
 
diff --git a/src/ast/rewriter/seq_axioms.cpp b/src/ast/rewriter/seq_axioms.cpp
index 93f1351765a..44389eb6ca4 100644
--- a/src/ast/rewriter/seq_axioms.cpp
+++ b/src/ast/rewriter/seq_axioms.cpp
@@ -682,7 +682,7 @@ namespace seq {
         // itos(n) does not start with "0" when n > 0
         // n = 0 or at(itos(n),0) != "0"
         // alternative: n >= 0 => itos(stoi(itos(n))) = itos(n)
-        expr_ref zs(seq.str.mk_string(symbol("0")), m);
+        expr_ref zs(seq.str.mk_string("0"), m);
         m_rewrite(zs);
         expr_ref eq0 = mk_eq(n, zero);
         expr_ref at0 = mk_eq(seq.str.mk_at(e, zero), zs);
diff --git a/src/ast/rewriter/seq_rewriter.cpp b/src/ast/rewriter/seq_rewriter.cpp
index 8c0b729600f..0ca46f082dc 100644
--- a/src/ast/rewriter/seq_rewriter.cpp
+++ b/src/ast/rewriter/seq_rewriter.cpp
@@ -2159,7 +2159,7 @@ br_status seq_rewriter::mk_str_from_code(expr* a, expr_ref& result) {
     rational r;
     if (m_autil.is_numeral(a, r)) {
         if (r.is_neg() || r > u().max_char()) {
-            result = str().mk_string(symbol(""));
+            result = str().mk_string(zstring());
         }
         else {
             unsigned num = r.get_unsigned();
@@ -2207,10 +2207,10 @@ br_status seq_rewriter::mk_str_itos(expr* a, expr_ref& result) {
     rational r;
     if (m_autil.is_numeral(a, r)) {
         if (r.is_int() && !r.is_neg()) {
-            result = str().mk_string(symbol(r.to_string()));
+            result = str().mk_string(zstring(r));
         }
         else {
-            result = str().mk_string(symbol(""));
+            result = str().mk_string(zstring());
         }
         return BR_DONE;
     }
@@ -2225,7 +2225,7 @@ br_status seq_rewriter::mk_str_itos(expr* a, expr_ref& result) {
             eqs.push_back(m().mk_eq(b, str().mk_string(s)));
         }
         result = m().mk_or(eqs);
-        result = m().mk_ite(result, b, str().mk_string(symbol("")));
+        result = m().mk_ite(result, b, str().mk_string(zstring()));
         return BR_REWRITE2;
     }
     return BR_FAILED;
diff --git a/src/ast/seq_decl_plugin.cpp b/src/ast/seq_decl_plugin.cpp
index 048e6ffed59..8536583e638 100644
--- a/src/ast/seq_decl_plugin.cpp
+++ b/src/ast/seq_decl_plugin.cpp
@@ -375,7 +375,7 @@ func_decl * seq_decl_plugin::mk_func_decl(decl_kind k, unsigned num_parameters,
     case OP_SEQ_EMPTY:
         match(*m_sigs[k], arity, domain, range, rng);
         if (rng == m_string) {
-            parameter param(symbol(""));
+            parameter param(zstring(""));
             return mk_func_decl(OP_STRING_CONST, 1, &param, 0, nullptr, m_string);
         }
         else {
@@ -474,7 +474,7 @@ func_decl * seq_decl_plugin::mk_func_decl(decl_kind k, unsigned num_parameters,
         m.raise_exception("Incorrect arguments used for re.^. Expected one non-negative integer parameter");
 
     case OP_STRING_CONST:
-        if (!(num_parameters == 1 && arity == 0 && parameters[0].is_symbol())) {
+        if (!(num_parameters == 1 && arity == 0 && parameters[0].is_zstring())) {
             m.raise_exception("invalid string declaration");
         }
         return m.mk_const_decl(m_stringc_sym, m_string,
@@ -630,16 +630,8 @@ void seq_decl_plugin::get_sort_names(svector<builtin_name> & sort_names, symbol
     sort_names.push_back(builtin_name("StringSequence", _STRING_SORT));
 }
 
-app* seq_decl_plugin::mk_string(symbol const& s) {
-    parameter param(s);
-    func_decl* f = m_manager->mk_const_decl(m_stringc_sym, m_string,
-                                            func_decl_info(m_family_id, OP_STRING_CONST, 1, &param));
-    return m_manager->mk_const(f);
-}
-
 app* seq_decl_plugin::mk_string(zstring const& s) {
-    symbol sym(s.encode());
-    parameter param(sym);
+    parameter param(s);
     func_decl* f = m_manager->mk_const_decl(m_stringc_sym, m_string,
                                             func_decl_info(m_family_id, OP_STRING_CONST, 1, &param));
     return m_manager->mk_const(f);
@@ -792,7 +784,7 @@ app* seq_util::mk_lt(expr* ch1, expr* ch2) const {
 
 bool seq_util::str::is_string(func_decl const* f, zstring& s) const {
     if (is_string(f)) {
-        s = zstring(f->get_parameter(0).get_symbol().bare_str());
+        s = f->get_parameter(0).get_zstring();
         return true;
     }
     else {
diff --git a/src/ast/seq_decl_plugin.h b/src/ast/seq_decl_plugin.h
index 16b8e76db16..9adb4df3213 100644
--- a/src/ast/seq_decl_plugin.h
+++ b/src/ast/seq_decl_plugin.h
@@ -191,7 +191,6 @@ class seq_decl_plugin : public decl_plugin {
     unsigned max_char() const { return get_char_plugin().max_char(); }
     unsigned num_bits() const { return get_char_plugin().num_bits(); }
 
-    app* mk_string(symbol const& s);
     app* mk_string(zstring const& s);
     app* mk_char(unsigned ch);
 
@@ -262,9 +261,6 @@ class seq_util {
         ast_manager& m;
         family_id    m_fid;
 
-        app* mk_string(char const* s) { return mk_string(symbol(s)); }
-        app* mk_string(std::string const& s) { return mk_string(symbol(s.c_str())); }
-
 
     public:
         str(seq_util& u): u(u), m(u.m), m_fid(u.m_fid) {}
@@ -273,7 +269,6 @@ class seq_util {
         sort* mk_string_sort() const { return m.mk_sort(m_fid, _STRING_SORT, 0, nullptr); }
         app* mk_empty(sort* s) const { return m.mk_const(m.mk_func_decl(m_fid, OP_SEQ_EMPTY, 0, nullptr, 0, (expr*const*)nullptr, s)); }
         app* mk_string(zstring const& s) const;
-        app* mk_string(symbol const& s) const { return u.seq.mk_string(s); }
         app* mk_char(unsigned ch) const;
         app* mk_concat(expr* a, expr* b) const { expr* es[2] = { a, b }; return m.mk_app(m_fid, OP_SEQ_CONCAT, 2, es); }
         app* mk_concat(expr* a, expr* b, expr* c) const { return mk_concat(a, mk_concat(b, c)); }
@@ -313,14 +308,12 @@ class seq_util {
         bool is_skolem(func_decl const* f)      const { return is_decl_of(f, m_fid, _OP_SEQ_SKOLEM); }
 
         bool is_string(expr const * n) const { return is_app_of(n, m_fid, OP_STRING_CONST); }
-        bool is_string(expr const* n, symbol& s) const {
-            return is_string(n) && (s = to_app(n)->get_decl()->get_parameter(0).get_symbol(), true);
-        }
         bool is_string(func_decl const* f) const { return is_decl_of(f, m_fid, OP_STRING_CONST); }
         bool is_string(expr const* n, zstring& s) const;
         bool is_string(func_decl const* f, zstring& s) const;
-        bool is_empty(expr const* n) const { symbol s;
-            return is_app_of(n, m_fid, OP_SEQ_EMPTY) || (is_string(n, s) && !s.is_numerical() && *s.bare_str() == 0);
+        bool is_empty(expr const* n) const {
+            zstring s;
+            return is_app_of(n, m_fid, OP_SEQ_EMPTY) || (is_string(n, s) && s.empty());
         }
         bool is_concat(expr const* n)   const { return is_app_of(n, m_fid, OP_SEQ_CONCAT); }
         bool is_length(expr const* n)   const { return is_app_of(n, m_fid, OP_SEQ_LENGTH); }
diff --git a/src/model/seq_factory.h b/src/model/seq_factory.h
index d40a7f7bdc4..f5046b384ed 100644
--- a/src/model/seq_factory.h
+++ b/src/model/seq_factory.h
@@ -67,8 +67,8 @@ class seq_factory : public value_factory {
     }
     bool get_some_values(sort* s, expr_ref& v1, expr_ref& v2) override {
         if (u.is_string(s)) {
-            v1 = u.str.mk_string(symbol("a"));
-            v2 = u.str.mk_string(symbol("b"));
+            v1 = u.str.mk_string("a");
+            v2 = u.str.mk_string("b");
             return true;
         }
         sort* ch;
@@ -94,10 +94,11 @@ class seq_factory : public value_factory {
             while (true) {
                 std::ostringstream strm;
                 strm << m_unique_delim << std::hex << m_next++ << std::dec << m_unique_delim;
-                symbol sym(strm.str());
+                std::string s(strm.str());
+                symbol sym(s);
                 if (m_strings.contains(sym)) continue;
                 m_strings.insert(sym);
-                return u.str.mk_string(sym);
+                return u.str.mk_string(s);
             }
         }
         sort* seq = nullptr, *ch = nullptr;
@@ -131,8 +132,9 @@ class seq_factory : public value_factory {
         return nullptr;
     }
     void register_value(expr* n) override {
-        symbol sym;
-        if (u.str.is_string(n, sym)) {
+        zstring s;
+        if (u.str.is_string(n, s)) {
+            symbol sym(s.encode());
             m_strings.insert(sym);
             if (sym.str().find(m_unique_delim) != std::string::npos) 
                 add_new_delim();
diff --git a/src/parsers/smt2/smt2parser.cpp b/src/parsers/smt2/smt2parser.cpp
index 596cb8af90e..344c61283f9 100644
--- a/src/parsers/smt2/smt2parser.cpp
+++ b/src/parsers/smt2/smt2parser.cpp
@@ -1188,7 +1188,7 @@ namespace smt2 {
 
         void parse_string_const() {
             SASSERT(curr() == scanner::STRING_TOKEN);
-            zstring zs(m_scanner.get_string(), true);
+            zstring zs(m_scanner.get_string());
             expr_stack().push_back(sutil().str.mk_string(zs));
             TRACE("smt2parser", tout << "new string: " << mk_pp(expr_stack().back(), m()) << "\n";);
             next();
diff --git a/src/smt/theory_str.cpp b/src/smt/theory_str.cpp
index 6ef086b6098..e5c1469a6fc 100644
--- a/src/smt/theory_str.cpp
+++ b/src/smt/theory_str.cpp
@@ -190,8 +190,7 @@ namespace smt {
     }
 
     expr * theory_str::mk_string(const char * str) {
-        symbol sym(str);
-        return u.str.mk_string(sym);
+        return u.str.mk_string(str);
     }
 
     void theory_str::collect_statistics(::statistics & st) const {
diff --git a/src/smt/theory_str.h b/src/smt/theory_str.h
index 14356f8a17f..d96a4e4aff1 100644
--- a/src/smt/theory_str.h
+++ b/src/smt/theory_str.h
@@ -53,11 +53,11 @@ class str_value_factory : public value_factory {
         u(m), delim("!"), m_next(0) {}
     ~str_value_factory() override {}
     expr * get_some_value(sort * s) override {
-        return u.str.mk_string(symbol("some value"));
+        return u.str.mk_string("some value");
     }
     bool get_some_values(sort * s, expr_ref & v1, expr_ref & v2) override {
-        v1 = u.str.mk_string(symbol("value 1"));
-        v2 = u.str.mk_string(symbol("value 2"));
+        v1 = u.str.mk_string("value 1");
+        v2 = u.str.mk_string("value 2");
         return true;
     }
     expr * get_fresh_value(sort * s) override {
@@ -65,10 +65,11 @@ class str_value_factory : public value_factory {
             while (true) {
                 std::ostringstream strm;
                 strm << delim << std::hex << (m_next++) << std::dec << delim;
-                symbol sym(strm.str());
+                std::string s(strm.str());
+                symbol sym(s);
                 if (m_strings.contains(sym)) continue;
                 m_strings.insert(sym);
-                return u.str.mk_string(sym);
+                return u.str.mk_string(s);
             }
         }
         sort* seq = nullptr;
diff --git a/src/smt/theory_str_mc.cpp b/src/smt/theory_str_mc.cpp
index 8979a7a379b..49efa107738 100644
--- a/src/smt/theory_str_mc.cpp
+++ b/src/smt/theory_str_mc.cpp
@@ -1337,9 +1337,8 @@ namespace smt {
                             rw(arg_subst);
                             TRACE("str_fl", tout << "ival = " << ival << ", string arg evaluates to " << mk_pp(arg_subst, m) << std::endl;);
 
-                            symbol arg_str;
-                            if (u.str.is_string(arg_subst, arg_str)) {
-                                zstring arg_zstr(arg_str.bare_str());
+                            zstring arg_zstr;
+                            if (u.str.is_string(arg_subst, arg_zstr)) {
                                 rational arg_value;
                                 if (string_integer_conversion_valid(arg_zstr, arg_value)) {
                                     if (ival != arg_value) {
@@ -1365,9 +1364,8 @@ namespace smt {
                             (*replacer)(arg, arg_subst);
                             rw(arg_subst);
                             TRACE("str_fl", tout << "ival = " << ival << ", string arg evaluates to " << mk_pp(arg_subst, m) << std::endl;);
-                            symbol arg_str;
-                            if (u.str.is_string(arg_subst, arg_str)) {
-                                zstring arg_zstr(arg_str.bare_str());
+                            zstring arg_zstr;
+                            if (u.str.is_string(arg_subst, arg_zstr)) {
                                 if (ival >= rational::zero() && ival <= rational(u.max_char())) {
                                     // check that arg_subst has length 1 and that the codepoints are the same
                                     if (arg_zstr.length() != 1 || rational(arg_zstr[0]) != ival) {
@@ -1396,9 +1394,8 @@ namespace smt {
                             rw(e_subst);
                             TRACE("str_fl", tout << "ival = " << ival << ", string arg evaluates to " << mk_pp(e_subst, m) << std::endl;);
 
-                            symbol e_str;
-                            if (u.str.is_string(e_subst, e_str)) {
-                                zstring e_zstr(e_str.bare_str());
+                            zstring e_zstr;
+                            if (u.str.is_string(e_subst, e_zstr)) {
                                 // if arg is negative, e must be empty
                                 // if arg is non-negative, e must be valid AND cannot contain leading zeroes
 
@@ -1436,9 +1433,8 @@ namespace smt {
                             (*replacer)(e, e_subst);
                             rw(e_subst);
                             TRACE("str_fl", tout << "ival = " << ival << ", string arg evaluates to " << mk_pp(e_subst, m) << std::endl;);
-                            symbol e_str;
-                            if (u.str.is_string(e_subst, e_str)) {
-                                zstring e_zstr(e_str.bare_str());
+                            zstring e_zstr;
+                            if (u.str.is_string(e_subst, e_zstr)) {
                                 // if arg is out of range, e must be empty
                                 // if arg is in range, e must be valid
                                 if (ival <= rational::zero() || ival >= rational(u.max_char())) {
diff --git a/src/util/zstring.cpp b/src/util/zstring.cpp
index 5a57ec862c9..d5f12353317 100644
--- a/src/util/zstring.cpp
+++ b/src/util/zstring.cpp
@@ -33,7 +33,7 @@ static bool is_hex_digit(char ch, unsigned& d) {
     return false;
 }
 
-bool zstring::is_escape_char(bool from_input, char const *& s, unsigned& result) {
+bool zstring::is_escape_char(char const *& s, unsigned& result) {
     unsigned d;
     if (*s == '\\' && s[1] == 'u' && s[2] == '{' && s[3] != '}') {
         result = 0;
@@ -55,8 +55,6 @@ bool zstring::is_escape_char(bool from_input, char const *& s, unsigned& result)
         }
         return false;
     }
-    if (!from_input)
-        return false;
     unsigned d1, d2, d3, d4;
     if (*s == '\\' && s[1] == 'u' && 
         is_hex_digit(s[2], d1) &&
@@ -75,10 +73,10 @@ bool zstring::is_escape_char(bool from_input, char const *& s, unsigned& result)
     return false;
 }
 
-zstring::zstring(char const* s, bool from_input) {
+zstring::zstring(char const* s) {
     while (*s) {
         unsigned ch = 0;
-        if (is_escape_char(from_input, s, ch)) {
+        if (is_escape_char(s, ch)) {
             m_buffer.push_back(ch);
         }
         else {
@@ -89,6 +87,7 @@ zstring::zstring(char const* s, bool from_input) {
     SASSERT(well_formed());
 }
 
+
 bool zstring::uses_unicode() const {
     return gparams::get_value("unicode") != "false";
 }
@@ -236,12 +235,17 @@ zstring zstring::extract(unsigned offset, unsigned len) const {
     return result;
 }
 
+unsigned zstring::hash() const {
+    return unsigned_ptr_hash(m_buffer.data(), m_buffer.size(), 23);
+}
+
 zstring zstring::operator+(zstring const& other) const {
     zstring result(*this);
     result.m_buffer.append(other.m_buffer);
     return result;
 }
 
+
 bool zstring::operator==(const zstring& other) const {
     // two strings are equal iff they have the same length and characters
     if (length() != other.length()) {
diff --git a/src/util/zstring.h b/src/util/zstring.h
index f69a74ba5c8..7531390c86b 100644
--- a/src/util/zstring.h
+++ b/src/util/zstring.h
@@ -19,21 +19,23 @@ Module Name:
 #include <string>
 #include "util/vector.h"
 #include "util/buffer.h"
+#include "util/rational.h"
 
 class zstring {
 private:
     buffer<unsigned> m_buffer;
     bool well_formed() const;
     bool uses_unicode() const;
-    bool is_escape_char(bool from_input, char const *& s, unsigned& result);
+    bool is_escape_char(char const *& s, unsigned& result);
 public:
     static unsigned unicode_max_char() { return 196607; }
     static unsigned unicode_num_bits() { return 18; }
     static unsigned ascii_max_char() { return 255; }
     static unsigned ascii_num_bits() { return 8; }
     zstring() {}
-    zstring(char const* s, bool from_input);
-    zstring(const std::string &str) : zstring(str.c_str(), false) {}
+    zstring(char const* s);
+    zstring(const std::string &str) : zstring(str.c_str()) {}
+    zstring(rational const& r): zstring(r.to_string()) {}
     zstring(unsigned sz, unsigned const* s) { m_buffer.append(sz, s); SASSERT(well_formed()); }
     zstring(unsigned ch);
     zstring replace(zstring const& src, zstring const& dst) const;
@@ -51,6 +53,7 @@ class zstring {
     zstring operator+(zstring const& other) const;
     bool operator==(const zstring& other) const;
     bool operator!=(const zstring& other) const;
+    unsigned hash() const;
 
     friend std::ostream& operator<<(std::ostream &os, const zstring &str);
     friend bool operator<(const zstring& lhs, const zstring& rhs);