1 files changed, 65 insertions, 0 deletions
diff --git a/include/mbgl/style/expression/parse.hpp b/include/mbgl/style/expression/parse.hpp
new file mode 100644
index 0000000000..3d7fad70b3
--- /dev/null
+++ b/include/mbgl/style/expression/parse.hpp
@@ -0,0 +1,65 @@
+#pragma once
+
+#include <memory>
+#include <mbgl/style/expression/parsing_context.hpp>
+#include <mbgl/style/expression/expression.hpp>
+#include <mbgl/style/conversion.hpp>
+
+namespace mbgl {
+namespace style {
+namespace expression {
+
+using namespace mbgl::style;
+
+template <class V>
+std::string getJSType(const V& value) {
+    using namespace mbgl::style::conversion;
+    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"; }
+    );
+}
+
+using ParseResult = variant<CompileError, std::unique_ptr<Expression>>;
+
+template <class V>
+ParseResult parseExpression(const V& value, const ParsingContext& context)
+{
+    using namespace mbgl::style::conversion;
+    
+    if (isArray(value)) {
+        if (arrayLength(value) == 0) {
+            CompileError error = {
+                "Expected an array with at least one element. If you wanted a literal array, use [\"literal\", []].",
+                context.key()
+            };
+            return error;
+        }
+        
+        const optional<std::string>& op = toString(arrayMember(value, 0));
+        if (!op) {
+            CompileError error = {
+                "Expression name must be a string, but found " + getJSType(arrayMember(value, 0)) +
+                    " instead. If you wanted a literal array, use [\"literal\", [...]].",
+                context.key(0)
+            };
+            return error;
+        }
+    }
+
+    return LiteralExpression::parse(value, context);
+}
+
+
+} // namespace expression
+} // namespace style
+} // namespace mbgl