Add ite expression

This introduces Conditional expression constructs.

Issue #67

share/input.rng

@@ -632,6 +632,7 @@
     <choice>
       <ref name="numerical-operation"/>
       <ref name="Boolean-operation"/>
+      <ref name="conditional-operation"/>
     </choice>
   </define>
 
@@ -837,6 +838,19 @@
     <!-- V.2.5. Conditional Expressions -->
     <!-- *********************************************************** -->
 
+  <define name="conditional-operation">
+    <choice>
+      <ref name="if-then-else-operation"/>
+    </choice>
+  </define>
+
+  <define name="if-then-else-operation">
+    <element name="ite">
+      <ref name="expression"/>
+      <ref name="expression"/>
+      <ref name="expression"/>
+    </element>
+  </define>
 
     <!-- *********************************************************** -->
     <!-- V.2.6. Built-ins -->

src/CMakeLists.txt

@@ -32,6 +32,7 @@ set(SCRAM_CORE_SRC
   "${CMAKE_CURRENT_SOURCE_DIR}/element.cc"
   "${CMAKE_CURRENT_SOURCE_DIR}/expression.cc"
   "${CMAKE_CURRENT_SOURCE_DIR}/parameter.cc"
+  "${CMAKE_CURRENT_SOURCE_DIR}/expression/conditional.cc"
   "${CMAKE_CURRENT_SOURCE_DIR}/expression/constant.cc"
   "${CMAKE_CURRENT_SOURCE_DIR}/expression/numerical.cc"
   "${CMAKE_CURRENT_SOURCE_DIR}/expression/exponential.cc"

src/expression/conditional.cc

@@ -0,0 +1,38 @@
+/*
+ * Copyright (C) 2017 Olzhas Rakhimov
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/// @file conditional.cc
+/// Implementation of conditional expressions.
+
+#include "conditional.h"
+
+#include <algorithm>
+
+namespace scram {
+namespace mef {
+
+Interval Ite::interval() noexcept {
+  assert(args().size() == 3);
+  Interval then_interval = args()[1]->interval();
+  Interval else_interval = args()[2]->interval();
+  return Interval::closed(
+      std::min(then_interval.lower(), else_interval.lower()),
+      std::max(then_interval.upper(), else_interval.upper()));
+}
+
+}  // namespace mef
+}  // namespace scram

src/expression/conditional.h

@@ -0,0 +1,51 @@
+/*
+ * Copyright (C) 2017 Olzhas Rakhimov
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/// @file conditional.h
+/// Conditional (if-then-else, switch-case) expressions.
+
+#ifndef SCRAM_SRC_EXPRESSION_CONDITIONAL_H_
+#define SCRAM_SRC_EXPRESSION_CONDITIONAL_H_
+
+#include "src/expression.h"
+
+namespace scram {
+namespace mef {
+
+/// If-Then-Else ternary expression.
+class Ite : public ExpressionFormula<Ite> {
+ public:
+  /// @param[in] condition  The Boolean expression to be tested.
+  /// @param[in] then_arm  The expression if the Boolean is true.
+  /// @param[in] else_arm  The expression if the Boolean is false.
+  Ite(Expression* condition, Expression* then_arm, Expression* else_arm)
+      : ExpressionFormula<Ite>({condition, then_arm, else_arm}) {}
+
+  Interval interval() noexcept override;
+
+  /// Computes the if-then-else expression with the given evaluator.
+  template <typename F>
+  double Compute(F&& eval) noexcept {
+    assert(args().size() == 3);
+    return eval(args()[0]) ? eval(args()[1]) : eval(args()[2]);
+  }
+};
+
+}  // namespace mef
+}  // namespace scram
+
+#endif  // SCRAM_SRC_EXPRESSION_CONDITIONAL_H_

src/initializer.cc

@@ -30,6 +30,7 @@
 #include "env.h"
 #include "error.h"
 #include "expression/boolean.h"
+#include "expression/conditional.h"
 #include "expression/exponential.h"
 #include "expression/numerical.h"
 #include "expression/random_deviate.h"
@@ -834,7 +835,8 @@ const Initializer::ExtractorMap Initializer::kExpressionExtractors_ = {
     {"lt", &Extract<Lt>},
     {"gt", &Extract<Gt>},
     {"leq", &Extract<Leq>},
-    {"geq", &Extract<Geq>}};
+    {"geq", &Extract<Geq>},
+    {"ite", &Extract<Ite>}};
 
 Expression* Initializer::GetExpression(const xmlpp::Element* expr_element,
                                        const std::string& base_path) {

tests/expression_tests.cc

@@ -17,6 +17,7 @@
 
 #include "expression.h"
 #include "expression/boolean.h"
+#include "expression/conditional.h"
 #include "expression/exponential.h"
 #include "expression/constant.h"
 #include "expression/numerical.h"
@@ -1150,6 +1151,22 @@ TEST(ExpressionTest, Geq) {
   EXPECT_DOUBLE_EQ(0, dev->value());
 }
 
+TEST(ExpressionTest, Ite) {
+  OpenExpression arg_one(1);
+  OpenExpression arg_two(42, 42, 32, 52);
+  OpenExpression arg_three(10, 10, 5, 15);
+  std::unique_ptr<Expression> dev;
+  ASSERT_NO_THROW(dev = std::make_unique<Ite>(&arg_one, &arg_two, &arg_three));
+  EXPECT_DOUBLE_EQ(42, dev->value());
+  arg_one.mean = 0;
+  EXPECT_DOUBLE_EQ(10, dev->value());
+  arg_one.mean = 0.5;
+  EXPECT_DOUBLE_EQ(42, dev->value());
+
+  EXPECT_TRUE(Interval::closed(5, 52) == dev->interval())
+      << dev->interval();
+}
+
 }  // namespace test
 }  // namespace mef
 }  // namespace scram

tests/input/fta/correct_expressions.xml

@@ -353,5 +353,12 @@ The input tries to utilize all the functionality including optional cases.
         <bool value="false"/>
       </geq>
     </define-parameter>
+    <define-parameter name="if-then-else">
+      <ite>
+        <bool value="true"/>
+        <int value="42"/>
+        <float value="-42"/>
+      </ite>
+    </define-parameter>
   </model-data>
 </opsa-mef>