Create a new interactive_t helper class

The purpose of this class is much like Emacs' (interactive) form: it
allows a value expression function to declare exactly how many
arguments, and of what type, it intends to receive.  It then offers
type-safe access to theese arguments in a consistent manner.

An example value expression function definition in C++:

    value_t fn_foo(call_scope_t& scope) {
      // We expect a string, an integer, and an optional date
      interactive_t args(scope, "sl&d");

      std::cout << "String  = " << args.get<string>(0)
                << "Integer = " << args.get<long>(1) << std::endl;

      if (args.has(2)) // was a date provided?
        std::cout << "Date    = " << args.get<date_t>(2) << std::endl;

      return NULL_VALUE;
    }

There is also an in_context_t<T> template, which finds the context type
T in the current scope hierarchy.  The in_context_t then also acts as a
smart pointer to reference this context object, in addition to serving
the same duty as interactive_t.  This combination of intent is solely
for the sake of brevity.

    value_t fn_bar(call_scope_t& scope) {
      in_context_t<account_t> env(scope, "sl&d");
      std::cout << "Account name = " << env->fullname()
                << "String arg   = " << env.get<string>(0)
                << std::endl;
      return NULL_VALUE;
    }

As you can see here, 'env' acts as a smart pointer to the required
context, and an object to extract the typed arguments.

1 files changed, 142 insertions, 0 deletions

diff --git a/src/interactive.h b/src/interactive.h
new file mode 100644
index 00000000..766953ec
--- /dev/null
+++ b/src/interactive.h
@@ -0,0 +1,142 @@
+/*
+ * Copyright (c) 2003-2009, John Wiegley.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the distribution.
+ *
+ * - Neither the name of New Artisans LLC nor the names of its
+ *   contributors may be used to endorse or promote products derived from
+ *   this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/**
+ * @addtogroup expr
+ */
+
+/**
+ * @file   interactive.h
+ * @author John Wiegley
+ *
+ * @ingroup expr
+ *
+ * @brief Brief
+ *
+ * Long.
+ */
+#ifndef _INTERACTIVE_H
+#define _INTERACTIVE_H
+
+#include "scope.h"
+
+namespace ledger {
+
+/**
+ * @brief Brief
+ *
+ * Long.
+ */
+class interactive_t : public noncopyable
+{
+  call_scope_t& args;
+  string        spec;
+
+public:
+  explicit interactive_t(call_scope_t& _args, const string& _spec = "")
+    : args(_args), spec(_spec)  {
+    TRACE_CTOR(interactive_t, "call_scope_t&, const string&");
+    verify_arguments();
+  }
+  virtual ~interactive_t() {
+    TRACE_DTOR(interactive_t);
+  }
+
+  void verify_arguments() const;
+
+  bool has(std::size_t index) const {
+    if (index < args.size())
+      return true;
+    return false;
+  }
+
+  const value_t& value_at(std::size_t index) const {
+    assert(has(index));
+    return args[index];
+  }
+
+  template <typename T>
+  T get(std::size_t index) const;
+};
+
+template <>
+inline bool interactive_t::get<bool>(std::size_t index) const {
+  return value_at(index).to_boolean();
+}
+template <>
+inline long interactive_t::get<long>(std::size_t index) const {
+  return value_at(index).to_long();
+}
+template <>
+inline string interactive_t::get<string>(std::size_t index) const {
+  return value_at(index).to_string();
+}
+template <>
+inline mask_t interactive_t::get<mask_t>(std::size_t index) const {
+  return value_at(index).to_mask();
+}
+template <>
+inline date_t interactive_t::get<date_t>(std::size_t index) const {
+  return value_at(index).to_date();
+}
+template <>
+inline datetime_t interactive_t::get<datetime_t>(std::size_t index) const {
+  return value_at(index).to_datetime();
+}
+
+template <typename T>
+class in_context_t : public interactive_t
+{
+  T& context;
+
+public:
+  explicit in_context_t(call_scope_t& args, const string& spec)
+    : interactive_t(args, spec), context(find_scope<T>(args)) {
+    TRACE_CTOR(in_context_t, "call_scope_t&, const string&");
+  }
+  virtual ~in_context_t() {
+    TRACE_DTOR(in_context_t);
+  }
+
+  T& operator *() {
+    return context;
+  }
+  T * operator->() {
+    return &context;
+  }
+};
+
+string join_args(call_scope_t& args);
+
+} // namespace ledger
+
+#endif // _INTERACTIVE_H
+