1 files changed, 56 insertions, 0 deletions
diff --git a/include/mbgl/style/conversion/expression.hpp b/include/mbgl/style/conversion/expression.hpp
new file mode 100644
index 0000000000..d70e3e0b33
--- /dev/null
+++ b/include/mbgl/style/conversion/expression.hpp
@@ -0,0 +1,56 @@
+#pragma once
+
+#include <memory>
+#include <sstream>
+#include <mbgl/style/function/expression.hpp>
+#include <mbgl/style/conversion.hpp>
+
+namespace mbgl {
+namespace style {
+namespace conversion {
+
+using namespace mbgl::style::expression;
+
+template<> struct Converter<std::unique_ptr<Expression>> {
+    template <class V>
+    std::string getJSType(const V& value) const {
+        if (isUndefined(value)) {
+            return "undefined";
+        }
+        if (isArray(value) || isObject(value)) {
+            return "object";
+        }
+        optional<mbgl::Value> v = toValue(value);
+        assert(v);
+        return v->match(
+            [&] (std::string) { return "string"; },
+            [&] (bool) { return "boolean"; },
+            [&] (auto) { return "number"; }
+        );
+    }
+
+    template <class V>
+    optional<std::unique_ptr<Expression>> operator()(const V& value, Error& error) const {
+        if (isArray(value)) {
+            if (arrayLength(value) == 0) {
+                error = { "Expected an array with at least one element. If you wanted a literal array, use [\"literal\", []]." };
+                return {};
+            }
+            
+            const optional<std::string>& op = toString(arrayMember(value, 0));
+            if (!op) {
+                std::ostringstream ss;
+                ss << "Expression name must be a string, but found "
+                    << getJSType(arrayMember(value, 0))
+                    << " instead. If you wanted a literal array, use [\"literal\", [...]].";
+                error = { ss.str() };
+                return {};
+            }
+        }
+        return {std::make_unique<LiteralExpression>("", 1.0f)};
+    }
+};
+
+} // namespace conversion
+} // namespace style
+} // namespace mbgl