From 012597b112bf2498f63e028d1eaf1044146562d2 Mon Sep 17 00:00:00 2001
From: Roland Conybeare <rconybeare@gmail.com>
Date: Mon, 17 Jun 2024 12:26:24 -0400
Subject: [PATCH] xo-expression: + if-expressions

---
 include/xo/expression/IfExpr.hpp   | 67 ++++++++++++++++++++++++++++++
 include/xo/expression/exprtype.hpp |  3 ++
 src/expression/CMakeLists.txt      |  2 +-
 src/expression/IfExpr.cpp          | 20 +++++++++
 4 files changed, 91 insertions(+), 1 deletion(-)
 create mode 100644 include/xo/expression/IfExpr.hpp
 create mode 100644 src/expression/IfExpr.cpp

diff --git a/include/xo/expression/IfExpr.hpp b/include/xo/expression/IfExpr.hpp
new file mode 100644
index 00000000..d60ab1d3
--- /dev/null
+++ b/include/xo/expression/IfExpr.hpp
@@ -0,0 +1,67 @@
+/** @file IfExpr.hpp
+ *
+ *  Author: Roland Conybeare
+ **/
+
+#pragma once
+
+#include "Expression.hpp"
+#include <vector>
+#include <string>
+//#include <cstdint>
+
+namespace xo {
+    namespace ast {
+        /** @class IfExpr
+         *  @brief abstract syntax tree for a function definition
+         *
+         **/
+        class IfExpr : public Expression {
+        public:
+            /** @p test   test-expression;  always execute
+             *  @p when_true  then-branch;  executes only when test succeeds
+             *  @p when_false else-branch;  executes only when test fails
+             **/
+            IfExpr(const ref::rp<Expression> & test,
+                   const ref::rp<Expression> & when_true,
+                   const ref::rp<Expression> & when_false)
+                : Expression(exprtype::if_expr),
+                  test_{test},
+                  when_true_{when_true},
+                  when_false_{when_false} {}
+
+            /** downcast from Expression **/
+            static ref::brw<IfExpr> from(ref::brw<Expression> x) {
+                return ref::brw<IfExpr>::from(x);
+            }
+
+            const ref::rp<Expression> & test() const { return test_; }
+            const ref::rp<Expression> & when_true() const { return when_true_; }
+            const ref::rp<Expression> & when_false() const { return when_false_; }
+
+            // ----- Expression -----
+
+            virtual void display(std::ostream & os) const override;
+
+        private:
+            /** if:
+             *    (if x y z)
+             *
+             *  executes x;  if true execute y; otherwise execute z
+             **/
+            ref::rp<Expression> test_;
+            ref::rp<Expression> when_true_;
+            ref::rp<Expression> when_false_;
+        }; /*IfExpr*/
+
+        inline ref::rp<IfExpr>
+        make_if_expr(const ref::rp<Expression> & test,
+                     const ref::rp<Expression> & when_true,
+                     const ref::rp<Expression> & when_false)
+        {
+            return new IfExpr(test, when_true, when_false);
+        }
+    } /*namespace ast*/
+} /*namespace xo*/
+
+/** end IfExpr.hpp **/
diff --git a/include/xo/expression/exprtype.hpp b/include/xo/expression/exprtype.hpp
index 91bcfbb5..ee33190e 100644
--- a/include/xo/expression/exprtype.hpp
+++ b/include/xo/expression/exprtype.hpp
@@ -28,6 +28,8 @@ namespace xo {
             lambda,
             /** variable reference **/
             variable,
+            /** if-then-else **/
+            if_expr,
 
             /** not an expression.  comes last, counts entries **/
             n_expr
@@ -43,6 +45,7 @@ namespace xo {
             case exprtype::apply: return "apply";
             case exprtype::lambda: return "lambda";
             case exprtype::variable: return "variable";
+            case exprtype::if_expr: return "if_expr";
             default: break;
             }
 
diff --git a/src/expression/CMakeLists.txt b/src/expression/CMakeLists.txt
index 0ef351e1..ef5cf6f2 100644
--- a/src/expression/CMakeLists.txt
+++ b/src/expression/CMakeLists.txt
@@ -6,7 +6,7 @@ set(SELF_SRCS
     Apply.cpp
     Lambda.cpp
     Variable.cpp
-    #init_reflect.cpp
+    IfExpr.cpp
 )
 
 xo_add_shared_library4(${SELF_LIB} ${PROJECT_NAME}Targets ${PROJECT_VERSION} 1 ${SELF_SRCS})
diff --git a/src/expression/IfExpr.cpp b/src/expression/IfExpr.cpp
new file mode 100644
index 00000000..a12fbdb7
--- /dev/null
+++ b/src/expression/IfExpr.cpp
@@ -0,0 +1,20 @@
+/* @file IfExpr.cpp */
+
+#include "IfExpr.hpp"
+#include "xo/indentlog/print/vector.hpp"
+
+namespace xo {
+    namespace ast {
+        void
+        IfExpr::display(std::ostream & os) const {
+            os << "<IfExpr"
+               << xtag("test", test_)
+               << xtag("when_true", when_true_)
+               << xtag("when_false", when_false_)
+               << ">";
+        } /*display*/
+    } /*namespace ast*/
+} /*namespace xo*/
+
+
+/* end IfExpr.cpp */