xo-interpreter: repl example [wip]

xo-interpreter/example/CMakeLists.txt

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+add_subdirectory(replxx)

xo-interpreter/example/replxx/CMakeLists.txt

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+# xo-interpreter/example/replxx/CMakeLists.txt
+
+set(SELF_EXE xo_interpreter_replxx)
+set(SELF_SRCS replxx.cpp)
+
+if (XO_ENABLE_EXAMPLES)
+    xo_add_executable(${SELF_EXE} ${SELF_SRCS})
+    xo_self_dependency(${SELF_EXE} xo_interpreter)
+    # TODO: consider promoting to regular app
+    xo_dependency(${SELF_EXE} xo_reader)
+    xo_external_target_dependency(${SELF_EXE} replxx replxx::replxx)
+
+    find_package(Threads REQUIRED)
+    target_link_libraries(${SELF_EXE} PUBLIC Threads::Threads)
+endif()
+
+# end CMakeLists.txt

xo-interpreter/example/replxx/replxx.cpp

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+/** @file replxx.cpp **/
+
+#include "xo/reader/reader.hpp"
+#include <replxx.hxx>
+#include <iostream>
+#include <unistd.h> // for isatty
+
+// similar helper in exprreplxx.cpp
+//
+bool replxx_getline(bool interactive,
+                    std::size_t parser_stack_size,
+                    replxx::Replxx & rx,
+                    std::string & input)
+{
+    using namespace std;
+
+    char const * prompt = "";
+
+    if (interactive) {
+        if (parser_stack_size <= 1)
+            prompt = "> ";
+        else
+            prompt = ". ";
+    }
+
+    /* input_cstr: next line of input from replxx library */
+    const char * input_cstr = rx.input(prompt);
+
+    bool retval = (input_cstr != nullptr);
+
+    if (retval) {
+        /* got new input */
+        input = input_cstr;
+    }
+
+    rx.history_add(input);
+
+    input.push_back('\n');
+
+    return retval;
+}
+
+void
+welcome(std::ostream & os)
+{
+    using namespace std;
+
+    os << "read-eval-print loop for schematika expressions" << endl;
+    os << "  ctrl-a/ctrl-e   beginning/end of line" << endl;
+    os << "  ctrl-u          delete entire line" << endl;
+    os << "  ctrl-k          delete to end of line" << endl;
+    os << "  meta-<bs>       backward delete word" << endl;
+    os << "  <up>|meta-p     previous command from history" << endl;
+    os << "  <down>|meta-n   next command from history" << endl;
+    os << "  <pgup>/<pgdown> page through history faster" << endl;
+    os << "  ctrl-s/ctrl-r   forward/backward history search" << endl;
+    os << endl;
+}
+
+int
+main()
+{
+    using namespace replxx;
+    using namespace xo::scm;
+    using xo::scm::Expression;
+    using xo::print::ppconfig;
+    using xo::print::ppstate_standalone;
+    using xo::rp;
+    using namespace std;
+
+    using span_type = xo::scm::span<const char>;
+
+    bool interactive = isatty(STDIN_FILENO);
+
+    Replxx rx;
+    rx.set_max_history_size(1000);
+    rx.history_load("repl_history.txt");
+//    rx.bind_key_internal(Replxx::KEY::control('p'), "history_previous");
+//    rx.bind_key_internal(Replxx::KEY::control('n'), "history_next");
+
+    constexpr bool c_debug_flag = false;
+
+    reader rdr(c_debug_flag);
+    rdr.begin_interactive_session();
+
+    string input_str;
+
+    bool eof = false;
+
+    span_type input;
+    std::size_t parser_stack_size = 0;
+
+    welcome(cerr);
+
+    while (replxx_getline(interactive, parser_stack_size, rx, input_str)) {
+        input  = span_type::from_string(input_str);
+
+        while (!input.empty()) {
+            auto [expr, consumed, psz, error] = rdr.read_expr(input, eof);
+
+            if (expr) {
+                ppconfig ppc;
+                ppstate_standalone pps(&cout, 0, &ppc);
+
+                pps.prettyn(expr);
+            } else if (error.is_error()) {
+                cout << "parsing error (detected in " << error.src_function() << "): " << endl;
+                error.report(cout);
+
+                /* discard stashed remainder of input line
+                 * (for nicely-formatted errors)
+                 */
+                rdr.reset_to_idle_toplevel();
+                break;
+            }
+
+            input = input.after_prefix(consumed);
+            parser_stack_size = psz;
+        }
+
+        /* here: input.empty() or error encountered */
+
+    }
+
+    auto [expr, _1, _2, error] = rdr.read_expr(input, true /*eof*/);
+
+    if (expr) {
+        ppconfig ppc;
+        ppstate_standalone pps(&cout, 0, &ppc);
+
+        pps.prettyn<rp<Expression>>(rp<Expression>(expr));
+    } else if (error.is_error()) {
+        cout << "parsing error (detected in " << error.src_function() << "): " << endl;
+        error.report(cout);
+    }
+
+    rx.history_save("repl_history.txt");
+}
+
+/* end replxx.cpp */

xo-interpreter/include/xo/interpreter/Schematika.hpp

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+/** @file Schematika.hpp
+ *
+ *  @author Roland Conybeare, Nov 2025
+ **/
+
+#pramga once
+
+
+
+namespace xo {
+    namespace scm {
+
+        /** @class Schematika
+         *  @brief schematika interpreter state
+         **/
+        class Schematika {
+        public:
+            /** interactive read-eval-print loop.
+             *  Uses replxx to read from stdin.
+             *  If stdin is interactive, accepts line editing commands:
+             *  - ctrl-a          goto beginning of line
+             *  - ctrl-e          goto end of line
+             *  - ctrl-k          delete to end of line
+             *  - meta-<bs>       backwards delete word
+             *  - meta-p|<up>     retrieve previous command from history
+             *  - meta-n|<down>   retrieve next command from history
+             *  - <pgup>/<pgdown> page through history faster
+             *  - ctrl-s          forward history search
+             *  - ctrl-r          backward history search
+             **/
+            void interactive_repl();
+
+        private:
+            class Impl;
+            std::unique_ptr<Impl> p_impl_;
+        };
+    }
+}
+
+/* end Schematika.hpp */