[core] Convert legacy functions directly to expressions

12 files changed, 64 insertions, 966 deletions

diff --git a/include/mbgl/style/conversion/function.hpp b/include/mbgl/style/conversion/function.hpp
index 932925c53c..5ddede324b 100644
--- a/include/mbgl/style/conversion/function.hpp
+++ b/include/mbgl/style/conversion/function.hpp
@@ -3,224 +3,15 @@
 #include <mbgl/style/function/camera_function.hpp>
 #include <mbgl/style/function/source_function.hpp>
 #include <mbgl/style/function/composite_function.hpp>
-#include <mbgl/style/function/convert.hpp>
-#include <mbgl/style/function/categorical_stops.hpp>
-#include <mbgl/style/function/exponential_stops.hpp>
-#include <mbgl/style/function/interval_stops.hpp>
-#include <mbgl/style/function/identity_stops.hpp>
-#include <mbgl/style/function/composite_exponential_stops.hpp>
-#include <mbgl/style/function/composite_interval_stops.hpp>
-#include <mbgl/style/function/composite_categorical_stops.hpp>
 #include <mbgl/style/conversion.hpp>
 #include <mbgl/style/conversion/constant.hpp>
-#include <mbgl/util/ignore.hpp>
-#include <mbgl/util/variant.hpp>
+#include <mbgl/style/expression/expression.hpp>
+#include <mbgl/style/expression/value.hpp>
 
 namespace mbgl {
 namespace style {
 namespace conversion {
 
-template <class D, class R>
-optional<std::map<D, R>> convertStops(const Convertible& value, Error& error) {
-    auto stopsValue = objectMember(value, "stops");
-    if (!stopsValue) {
-        error = { "function value must specify stops" };
-        return {};
-    }
-
-    if (!isArray(*stopsValue)) {
-        error = { "function stops must be an array" };
-        return {};
-    }
-
-    if (arrayLength(*stopsValue) == 0) {
-        error = { "function must have at least one stop" };
-        return {};
-    }
-
-    std::map<D, R> stops;
-    for (std::size_t i = 0; i < arrayLength(*stopsValue); ++i) {
-        const auto& stopValue = arrayMember(*stopsValue, i);
-
-        if (!isArray(stopValue)) {
-            error = { "function stop must be an array" };
-            return {};
-        }
-
-        if (arrayLength(stopValue) != 2) {
-            error = { "function stop must have two elements" };
-            return {};
-        }
-
-        optional<D> d = convert<D>(arrayMember(stopValue, 0), error);
-        if (!d) {
-            return {};
-        }
-
-        optional<R> r = convert<R>(arrayMember(stopValue, 1), error);
-        if (!r) {
-            return {};
-        }
-
-        stops.emplace(*d, *r);
-    }
-
-    return stops;
-}
-
-template <class T>
-struct Converter<ExponentialStops<T>> {
-    static constexpr const char * type = "exponential";
-
-    optional<ExponentialStops<T>> operator()(const Convertible& value, Error& error) const {
-        auto stops = convertStops<float, T>(value, error);
-        if (!stops) {
-            return {};
-        }
-
-        auto baseValue = objectMember(value, "base");
-        if (!baseValue) {
-            return ExponentialStops<T>(*stops);
-        }
-
-        optional<float> base = toNumber(*baseValue);
-        if (!base) {
-            error = { "function base must be a number"};
-            return {};
-        }
-
-        return ExponentialStops<T>(*stops, *base);
-    }
-};
-
-template <class T>
-struct Converter<IntervalStops<T>> {
-    static constexpr const char * type = "interval";
-
-    optional<IntervalStops<T>> operator()(const Convertible& value, Error& error) const {
-        auto stops = convertStops<float, T>(value, error);
-        if (!stops) {
-            return {};
-        }
-        return IntervalStops<T>(*stops);
-    }
-};
-
-template <>
-struct Converter<CategoricalValue> {
-    optional<CategoricalValue> operator()(const Convertible& value, Error& error) const {
-        auto b = toBool(value);
-        if (b) {
-            return { *b };
-        }
-
-        auto n = toNumber(value);
-        if (n) {
-            return { int64_t(*n) };
-        }
-
-        auto s = toString(value);
-        if (s) {
-            return { *s };
-        }
-
-        error = { "stop domain value must be a number, string, or boolean" };
-        return {};
-    }
-};
-
-template <class T>
-struct Converter<CategoricalStops<T>> {
-    static constexpr const char * type = "categorical";
-
-    optional<CategoricalStops<T>> operator()(const Convertible& value, Error& error) const {
-        auto stops = convertStops<CategoricalValue, T>(value, error);
-        if (!stops) {
-            return {};
-        }
-        return CategoricalStops<T>(
-            std::map<CategoricalValue, T>((*stops).begin(), (*stops).end()));
-    }
-};
-
-template <class T>
-struct Converter<IdentityStops<T>> {
-    static constexpr const char * type = "identity";
-
-    optional<IdentityStops<T>> operator()(const Convertible&, Error&) const {
-        return IdentityStops<T>();
-    }
-};
-
-template <class, class>
-struct StopsConverter;
-
-template <class T, class... Ts>
-struct StopsConverter<T, variant<Ts...>> {
-public:
-    optional<variant<Ts...>> operator()(const Convertible& value, Error& error) const {
-        std::string type = util::Interpolatable<T>::value ? "exponential" : "interval";
-
-        auto typeValue = objectMember(value, "type");
-        if (typeValue && toString(*typeValue)) {
-            type = *toString(*typeValue);
-        }
-
-        bool matched = false;
-        optional<variant<Ts...>> result;
-
-        // Workaround for https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47226
-        auto tryConvert = [&] (auto* tp) {
-            using Stops = std::decay_t<decltype(*tp)>;
-            if (type == Converter<Stops>::type) {
-                matched = true;
-                optional<Stops> stops = convert<Stops>(value, error);
-                if (stops) {
-                    result = variant<Ts...>(*stops);
-                }
-            }
-        };
-
-        util::ignore({
-            (tryConvert((Ts*)nullptr), 0)...
-        });
-
-        if (!matched) {
-            error = { "unsupported function type" };
-            return {};
-        }
-
-        return result;
-    }
-};
-
-template <class T>
-struct Converter<CameraFunction<T>> {
-    optional<CameraFunction<T>> operator()(const Convertible& value, Error& error) const {
-        if (!isObject(value)) {
-            error = { "function must be an object" };
-            return {};
-        }
-
-        using Stops = std::conditional_t<
-            util::Interpolatable<T>::value,
-            variant<
-                ExponentialStops<T>,
-                IntervalStops<T>>,
-            variant<
-                IntervalStops<T>>>;
-
-        auto stops = StopsConverter<T, Stops>()(value, error);
-        if (!stops) {
-            return {};
-        }
-
-        return CameraFunction<T>((*stops).match([&] (const auto& s) {
-            return expression::Convert::toExpression(s);
-        }), false);
-    }
-};
-
 template <class T>
 optional<optional<T>> convertDefaultValue(const Convertible& value, Error& error) {
     auto defaultValueValue = objectMember(value, "default");
@@ -237,199 +28,48 @@ optional<optional<T>> convertDefaultValue(const Convertible& value, Error& error
     return { *defaultValue };
 }
 
-template <class T>
-struct Converter<SourceFunction<T>> {
-    optional<SourceFunction<T>> operator()(const Convertible& value, Error& error) const {
-        if (!isObject(value)) {
-            error = { "function must be an object" };
-            return {};
-        }
-
-        auto propertyValue = objectMember(value, "property");
-        if (!propertyValue) {
-            error = { "function must specify property" };
-            return {};
-        }
-
-        auto propertyString = toString(*propertyValue);
-        if (!propertyString) {
-            error = { "function property must be a string" };
-            return {};
-        }
-
-        using Stops = std::conditional_t<
-            util::Interpolatable<T>::value,
-            variant<
-                ExponentialStops<T>,
-                IntervalStops<T>,
-                CategoricalStops<T>,
-                IdentityStops<T>>,
-            variant<
-                IntervalStops<T>,
-                CategoricalStops<T>,
-                IdentityStops<T>>>;
-
-        auto stops = StopsConverter<T, Stops>()(value, error);
-        if (!stops) {
-            return {};
-        }
-
-        auto defaultValue = convertDefaultValue<T>(value, error);
-        if (!defaultValue) {
-            return {};
-        }
-
-        return SourceFunction<T>((*stops).match([&] (const auto& s) {
-            return expression::Convert::toExpression(*propertyString, s);
-        }), *defaultValue);
-    }
-};
-
-template <class S>
-struct CompositeValue : std::pair<float, S> {
-    using std::pair<float, S>::pair;
-};
-
-template <class S>
-struct Converter<CompositeValue<S>> {
-    optional<CompositeValue<S>> operator()(const Convertible& value, Error& error) const {
-        if (!isObject(value)) {
-            error = { "stop must be an object" };
-            return {};
-        }
-
-        auto zoomValue = objectMember(value, "zoom");
-        if (!zoomValue) {
-            error = { "stop must specify zoom" };
-            return {};
-        }
-
-        auto propertyValue = objectMember(value, "value");
-        if (!propertyValue) {
-            error = { "stop must specify value" };
-            return {};
-        }
-
-        optional<float> z = convert<float>(*zoomValue, error);
-        if (!z) {
-            return {};
-        }
-
-        optional<S> s = convert<S>(*propertyValue, error);
-        if (!s) {
-            return {};
-        }
-
-        return CompositeValue<S> { *z, *s };
-    }
-};
+optional<std::unique_ptr<expression::Expression>> convertCameraFunctionToExpression(expression::type::Type, const Convertible&, Error&);
+optional<std::unique_ptr<expression::Expression>> convertSourceFunctionToExpression(expression::type::Type, const Convertible&, Error&);
+optional<std::unique_ptr<expression::Expression>> convertCompositeFunctionToExpression(expression::type::Type, const Convertible&, Error&);
 
 template <class T>
-struct Converter<CompositeExponentialStops<T>> {
-    static constexpr const char * type = "exponential";
-
-    optional<CompositeExponentialStops<T>> operator()(const Convertible& value, Error& error) const {
-        auto stops = convertStops<CompositeValue<float>, T>(value, error);
-        if (!stops) {
+struct Converter<CameraFunction<T>> {
+    optional<CameraFunction<T>> operator()(const Convertible& value, Error& error) const {
+        auto expression = convertCameraFunctionToExpression(expression::valueTypeToExpressionType<T>(), value, error);
+        if (!expression) {
             return {};
         }
-
-        auto base = 1.0f;
-        auto baseValue = objectMember(value, "base");
-        if (baseValue && toNumber(*baseValue)) {
-            base = *toNumber(*baseValue);
-        }
-
-        std::map<float, std::map<float, T>> convertedStops;
-        for (const auto& stop : *stops) {
-            convertedStops[stop.first.first].emplace(stop.first.second, stop.second);
-        }
-
-        return CompositeExponentialStops<T>(convertedStops, base);
+        return CameraFunction<T>(std::move(*expression), false);
     }
 };
 
 template <class T>
-struct Converter<CompositeIntervalStops<T>> {
-    static constexpr const char * type = "interval";
-
-    optional<CompositeIntervalStops<T>> operator()(const Convertible& value, Error& error) const {
-        auto stops = convertStops<CompositeValue<float>, T>(value, error);
-        if (!stops) {
+struct Converter<SourceFunction<T>> {
+    optional<SourceFunction<T>> operator()(const Convertible& value, Error& error) const {
+        auto expression = convertSourceFunctionToExpression(expression::valueTypeToExpressionType<T>(), value, error);
+        if (!expression) {
             return {};
         }
-
-        std::map<float, std::map<float, T>> convertedStops;
-        for (const auto& stop : *stops) {
-            convertedStops[stop.first.first].emplace(stop.first.second, stop.second);
-        }
-
-        return CompositeIntervalStops<T>(convertedStops);
-    }
-};
-
-template <class T>
-struct Converter<CompositeCategoricalStops<T>> {
-    static constexpr const char * type = "categorical";
-
-    optional<CompositeCategoricalStops<T>> operator()(const Convertible& value, Error& error) const {
-        auto stops = convertStops<CompositeValue<CategoricalValue>, T>(value, error);
-        if (!stops) {
+        auto defaultValue = convertDefaultValue<T>(value, error);
+        if (!defaultValue) {
             return {};
         }
-
-        std::map<float, std::map<CategoricalValue, T>> convertedStops;
-        for (const auto& stop : *stops) {
-            convertedStops[stop.first.first].emplace(stop.first.second, stop.second);
-        }
-
-        return CompositeCategoricalStops<T>(convertedStops);
+        return SourceFunction<T>(std::move(*expression), *defaultValue);
     }
 };
 
 template <class T>
 struct Converter<CompositeFunction<T>> {
     optional<CompositeFunction<T>> operator()(const Convertible& value, Error& error) const {
-        if (!isObject(value)) {
-            error = { "function must be an object" };
+        auto expression = convertCompositeFunctionToExpression(expression::valueTypeToExpressionType<T>(), value, error);
+        if (!expression) {
             return {};
         }
-
-        auto propertyValue = objectMember(value, "property");
-        if (!propertyValue) {
-            error = { "function must specify property" };
-            return {};
-        }
-
-        auto propertyString = toString(*propertyValue);
-        if (!propertyString) {
-            error = { "function property must be a string" };
-            return {};
-        }
-
-        using Stops = std::conditional_t<
-            util::Interpolatable<T>::value,
-            variant<
-                CompositeExponentialStops<T>,
-                CompositeIntervalStops<T>,
-                CompositeCategoricalStops<T>>,
-            variant<
-                CompositeIntervalStops<T>,
-                CompositeCategoricalStops<T>>>;
-
-        auto stops = StopsConverter<T, Stops>()(value, error);
-        if (!stops) {
-            return {};
-        }
-
         auto defaultValue = convertDefaultValue<T>(value, error);
         if (!defaultValue) {
             return {};
         }
-
-        return CompositeFunction<T>((*stops).match([&] (const auto& s) {
-            return expression::Convert::toExpression(*propertyString, s);
-        }), *defaultValue);
+        return CompositeFunction<T>(std::move(*expression), *defaultValue);
     }
 };
 
diff --git a/include/mbgl/style/conversion/property_value.hpp b/include/mbgl/style/conversion/property_value.hpp
index dc1c32830f..e52c63d023 100644
--- a/include/mbgl/style/conversion/property_value.hpp
+++ b/include/mbgl/style/conversion/property_value.hpp
@@ -9,6 +9,7 @@
 #include <mbgl/style/expression/is_expression.hpp>
 #include <mbgl/style/expression/find_zoom_curve.hpp>
 #include <mbgl/style/expression/parsing_context.hpp>
+#include <mbgl/style/expression/literal.hpp>
 
 namespace mbgl {
 namespace style {
diff --git a/include/mbgl/style/expression/dsl.hpp b/include/mbgl/style/expression/dsl.hpp
index 8a5d1d84f5..22278b0975 100644
--- a/include/mbgl/style/expression/dsl.hpp
+++ b/include/mbgl/style/expression/dsl.hpp
@@ -5,6 +5,7 @@
 #include <mbgl/style/expression/interpolator.hpp>
 
 #include <memory>
+#include <string>
 #include <initializer_list>
 
 namespace mbgl {
@@ -15,6 +16,8 @@ namespace dsl {
 // This convenience API does little to no expression validation or type-checking, and is intended for
 // use only by test and other non-production code.
 
+std::unique_ptr<Expression> error(std::string);
+
 std::unique_ptr<Expression> literal(const char* value);
 std::unique_ptr<Expression> literal(Value value);
 std::unique_ptr<Expression> literal(std::initializer_list<double> value);
@@ -22,6 +25,7 @@ std::unique_ptr<Expression> literal(std::initializer_list<const char *> value);
 
 std::unique_ptr<Expression> number(std::unique_ptr<Expression>);
 std::unique_ptr<Expression> string(std::unique_ptr<Expression>);
+std::unique_ptr<Expression> boolean(std::unique_ptr<Expression>);
 
 std::unique_ptr<Expression> toColor(const char* value);
 std::unique_ptr<Expression> toColor(std::unique_ptr<Expression>);
diff --git a/include/mbgl/style/expression/error.hpp b/include/mbgl/style/expression/error.hpp
new file mode 100644
index 0000000000..bfb9247d11
--- /dev/null
+++ b/include/mbgl/style/expression/error.hpp
@@ -0,0 +1,39 @@
+#pragma once
+
+#include <mbgl/style/expression/expression.hpp>
+
+#include <string>
+
+namespace mbgl {
+namespace style {
+namespace expression {
+
+class Error : public Expression {
+public:
+    Error(std::string message_) 
+        : Expression(type::Error),
+          message(std::move(message_)) {}
+
+    void eachChild(const std::function<void(const Expression&)>&) const override {}
+
+    bool operator==(const Expression& e) const override {
+        return dynamic_cast<const Error*>(&e);
+    }
+
+    EvaluationResult evaluate(const EvaluationContext&) const override {
+        return EvaluationError{message};
+    }
+
+    std::vector<optional<Value>> possibleOutputs() const override {
+        return {};
+    }
+
+    std::string getOperator() const override { return "error"; }
+
+private:
+    std::string message;
+};
+
+} // namespace expression
+} // namespace style
+} // namespace mbgl
diff --git a/include/mbgl/style/function/categorical_stops.hpp b/include/mbgl/style/function/categorical_stops.hpp
deleted file mode 100644
index c8505115ab..0000000000
--- a/include/mbgl/style/function/categorical_stops.hpp
+++ /dev/null
@@ -1,40 +0,0 @@
-#pragma once
-
-#include <mbgl/util/feature.hpp>
-#include <mbgl/util/variant.hpp>
-
-#include <cassert>
-#include <utility>
-#include <map>
-
-namespace mbgl {
-namespace style {
-
-class CategoricalValue : public variant<bool, int64_t, std::string> {
-public:
-    using variant<bool, int64_t, std::string>::variant;
-};
-
-template <class T>
-class CategoricalStops {
-public:
-    using Stops = std::map<CategoricalValue, T>;
-
-    Stops stops;
-
-    CategoricalStops() = default;
-    CategoricalStops(Stops stops_)
-        : stops(std::move(stops_)) {
-        assert(stops.size() > 0);
-    }
-
-    optional<T> evaluate(const Value&) const;
-
-    friend bool operator==(const CategoricalStops& lhs,
-                           const CategoricalStops& rhs) {
-        return lhs.stops == rhs.stops;
-    }
-};
-
-} // namespace style
-} // namespace mbgl
diff --git a/include/mbgl/style/function/composite_categorical_stops.hpp b/include/mbgl/style/function/composite_categorical_stops.hpp
deleted file mode 100644
index b796621d1a..0000000000
--- a/include/mbgl/style/function/composite_categorical_stops.hpp
+++ /dev/null
@@ -1,30 +0,0 @@
-#pragma once
-
-#include <mbgl/style/function/categorical_stops.hpp>
-
-namespace mbgl {
-namespace style {
-
-template <class T>
-class CompositeCategoricalStops {
-public:
-    using Stops = std::map<float, std::map<CategoricalValue, T>>;
-    Stops stops;
-
-    CompositeCategoricalStops() = default;
-    CompositeCategoricalStops(Stops stops_)
-        : stops(std::move(stops_)) {
-    }
-
-    CategoricalStops<T> innerStops(const std::map<CategoricalValue, T>& stops_) const {
-        return CategoricalStops<T>(stops_);
-    }
-
-    friend bool operator==(const CompositeCategoricalStops& lhs,
-                           const CompositeCategoricalStops& rhs) {
-        return lhs.stops == rhs.stops;
-    }
-};
-
-} // namespace style
-} // namespace mbgl
diff --git a/include/mbgl/style/function/composite_exponential_stops.hpp b/include/mbgl/style/function/composite_exponential_stops.hpp
deleted file mode 100644
index f1ad32a04d..0000000000
--- a/include/mbgl/style/function/composite_exponential_stops.hpp
+++ /dev/null
@@ -1,35 +0,0 @@
-#pragma once
-
-#include <mbgl/style/function/exponential_stops.hpp>
-
-#include <map>
-
-namespace mbgl {
-namespace style {
-
-template <class T>
-class CompositeExponentialStops {
-public:
-    using Stops = std::map<float, std::map<float, T>>;
-
-    Stops stops;
-    float base = 1.0f;
-
-    CompositeExponentialStops() = default;
-    CompositeExponentialStops(Stops stops_, float base_ = 1.0f)
-        : stops(std::move(stops_)),
-          base(base_) {
-    }
-
-    ExponentialStops<T> innerStops(const std::map<float, T>& stops_) const {
-        return ExponentialStops<T>(stops_, base);
-    }
-
-    friend bool operator==(const CompositeExponentialStops& lhs,
-                           const CompositeExponentialStops& rhs) {
-        return lhs.stops == rhs.stops && lhs.base == rhs.base;
-    }
-};
-
-} // namespace style
-} // namespace mbgl
diff --git a/include/mbgl/style/function/composite_interval_stops.hpp b/include/mbgl/style/function/composite_interval_stops.hpp
deleted file mode 100644
index 3c495f2a7f..0000000000
--- a/include/mbgl/style/function/composite_interval_stops.hpp
+++ /dev/null
@@ -1,32 +0,0 @@
-#pragma once
-
-#include <mbgl/style/function/interval_stops.hpp>
-
-#include <map>
-
-namespace mbgl {
-namespace style {
-
-template <class T>
-class CompositeIntervalStops {
-public:
-    using Stops = std::map<float, std::map<float, T>>;
-    Stops stops;
-
-    CompositeIntervalStops() = default;
-    CompositeIntervalStops(Stops stops_)
-        : stops(std::move(stops_)) {
-    }
-
-    IntervalStops<T> innerStops(const std::map<float, T>& stops_) const {
-        return IntervalStops<T>(stops_);
-    }
-
-    friend bool operator==(const CompositeIntervalStops& lhs,
-                           const CompositeIntervalStops& rhs) {
-        return lhs.stops == rhs.stops;
-    }
-};
-
-} // namespace style
-} // namespace mbgl
diff --git a/include/mbgl/style/function/convert.hpp b/include/mbgl/style/function/convert.hpp
deleted file mode 100644
index a0dae992fa..0000000000
--- a/include/mbgl/style/function/convert.hpp
+++ /dev/null
@@ -1,322 +0,0 @@
-#pragma once
-
-#include <mbgl/style/expression/array_assertion.hpp>
-#include <mbgl/style/expression/assertion.hpp>
-#include <mbgl/style/expression/case.hpp>
-#include <mbgl/style/expression/coalesce.hpp>
-#include <mbgl/style/expression/compound_expression.hpp>
-#include <mbgl/style/expression/coercion.hpp>
-#include <mbgl/style/expression/interpolate.hpp>
-#include <mbgl/style/expression/expression.hpp>
-#include <mbgl/style/expression/literal.hpp>
-#include <mbgl/style/expression/match.hpp>
-#include <mbgl/style/expression/step.hpp>
-
-#include <mbgl/style/function/exponential_stops.hpp>
-#include <mbgl/style/function/interval_stops.hpp>
-#include <mbgl/style/function/categorical_stops.hpp>
-#include <mbgl/style/function/composite_exponential_stops.hpp>
-#include <mbgl/style/function/composite_interval_stops.hpp>
-#include <mbgl/style/function/composite_categorical_stops.hpp>
-#include <mbgl/style/function/identity_stops.hpp>
-
-#include <mbgl/util/enum.hpp>
-#include <mbgl/style/types.hpp>
-
-#include <string>
-
-
-namespace mbgl {
-namespace style {
-namespace expression {
-
-namespace detail {
-
-class ErrorExpression : public Expression {
-public:
-    ErrorExpression(std::string message_) : Expression(type::Error), message(std::move(message_)) {}
-    void eachChild(const std::function<void(const Expression&)>&) const override {}
-    
-    bool operator==(const Expression& e) const override {
-        return dynamic_cast<const ErrorExpression*>(&e);
-    }
-
-    EvaluationResult evaluate(const EvaluationContext&) const override {
-        return EvaluationError{message};
-    }
-
-    std::vector<optional<Value>> possibleOutputs() const override {
-        return {};
-    }
-
-    std::string getOperator() const override { return "error"; }
-private:
-    std::string message;
-};
-
-} // namespace detail
-
-
-// Create expressions representing 'classic' (i.e. stop-based) style functions
-
-struct Convert {
-    template <typename T>
-    static std::unique_ptr<Literal> makeLiteral(const T& value) {
-        return std::make_unique<Literal>(Value(toExpressionValue(value)));
-    }
-    
-    static std::unique_ptr<Expression> makeGet(type::Type type, const std::string& property) {
-        ParsingContext ctx;
-        std::vector<std::unique_ptr<Expression>> getArgs;
-        getArgs.push_back(makeLiteral(property));
-        ParseResult get = createCompoundExpression("get", std::move(getArgs), ctx);
-        assert(get);
-        assert(ctx.getErrors().size() == 0);
-
-        std::vector<std::unique_ptr<Expression>> assertionArgs;
-        assertionArgs.push_back(std::move(*get));
-        
-        return std::make_unique<Assertion>(type, std::move(assertionArgs));
-    }
-    
-    static std::unique_ptr<Expression> makeZoom() {
-        ParsingContext ctx;
-        ParseResult zoom = createCompoundExpression("zoom", std::vector<std::unique_ptr<Expression>>(), ctx);
-        assert(zoom);
-        assert(ctx.getErrors().size() == 0);
-        return std::move(*zoom);
-    }
-    
-    static std::unique_ptr<Expression> makeError(std::string message) {
-        return std::make_unique<detail::ErrorExpression>(message);
-    }
-    
-    template <typename Key>
-    static ParseResult makeMatch(type::Type type,
-                                 std::unique_ptr<Expression> input,
-                                 std::map<CategoricalValue, std::unique_ptr<Expression>> stops) {
-        // match expression
-        typename Match<Key>::Branches branches;
-        for(auto it = stops.begin(); it != stops.end(); it++) {
-            assert(it->first.template is<Key>());
-            Key key = it->first.template get<Key>();
-            branches.emplace(
-                std::move(key),
-                std::move(it->second)
-            );
-        }
-        
-        return ParseResult(std::make_unique<Match<Key>>(std::move(type),
-                                            std::move(input),
-                                            std::move(branches),
-                                            makeError("No matching label")));
-    }
-    
-    static ParseResult makeCase(type::Type type,
-                                std::unique_ptr<Expression> input,
-                                std::map<CategoricalValue, std::unique_ptr<Expression>> stops) {
-        // case expression
-        std::vector<typename Case::Branch> branches;
-        
-        auto it = stops.find(true);
-        std::unique_ptr<Expression> true_case = it == stops.end() ?
-            makeError("No matching label") :
-            std::move(it->second);
-
-        it = stops.find(false);
-        std::unique_ptr<Expression> false_case = it == stops.end() ?
-            makeError("No matching label") :
-            std::move(it->second);
-
-        branches.push_back(std::make_pair(std::move(input), std::move(true_case)));
-        return ParseResult(std::make_unique<Case>(std::move(type), std::move(branches), std::move(false_case)));
-    }
-    
-    template <typename T>
-    static ParseResult fromCategoricalStops(std::map<CategoricalValue, T> stops, const std::string& property) {
-        assert(stops.size() > 0);
-
-        std::map<CategoricalValue, std::unique_ptr<Expression>> convertedStops;
-        for(const std::pair<CategoricalValue, T>& stop : stops) {
-            convertedStops.emplace(
-                stop.first,
-                makeLiteral(stop.second)
-            );
-        }
-        
-        type::Type type = valueTypeToExpressionType<T>();
-
-        const CategoricalValue& firstKey = stops.begin()->first;
-        return firstKey.match(
-            [&](bool) {
-                return makeCase(type, makeGet(type::Boolean, property), std::move(convertedStops));
-            },
-            [&](const std::string&) {
-                return makeMatch<std::string>(type, makeGet(type::String, property), std::move(convertedStops));
-            },
-            [&](int64_t) {
-                return makeMatch<int64_t>(type, makeGet(type::Number, property), std::move(convertedStops));
-            }
-        );
-    }
-    
-    template <typename T>
-    static std::map<double, std::unique_ptr<Expression>> convertStops(const std::map<float, T>& stops) {
-        std::map<double, std::unique_ptr<Expression>> convertedStops;
-        for(const auto& stop : stops) {
-            convertedStops.emplace(
-                stop.first,
-                makeLiteral(stop.second)
-            );
-        }
-        return convertedStops;
-    }
-    
-    template <typename T>
-    static std::unique_ptr<Expression> toExpression(const ExponentialStops<T>& stops)
-    {
-        ParsingContext ctx;
-        ParseResult e = createInterpolate(valueTypeToExpressionType<T>(),
-                                          ExponentialInterpolator(stops.base),
-                                          makeZoom(),
-                                          convertStops(stops.stops),
-                                          ctx);
-        assert(e);
-        return std::move(*e);
-    }
-    
-    template <typename T>
-    static std::unique_ptr<Expression> toExpression(const IntervalStops<T>& stops)
-    {
-        ParseResult e(std::make_unique<Step>(valueTypeToExpressionType<T>(),
-                                             makeZoom(),
-                                             convertStops(stops.stops)));
-        assert(e);
-        return std::move(*e);
-    }
-    
-    template <typename T>
-    static std::unique_ptr<Expression> toExpression(const std::string& property,
-                                                  const ExponentialStops<T>& stops)
-    {
-        ParsingContext ctx;
-        ParseResult e = createInterpolate(valueTypeToExpressionType<T>(),
-                                          ExponentialInterpolator(stops.base),
-                                          makeGet(type::Number, property),
-                                          convertStops(stops.stops),
-                                          ctx);
-        assert(e);
-        return std::move(*e);
-    }
-    
-    template <typename T>
-    static std::unique_ptr<Expression> toExpression(const std::string& property,
-                                                  const IntervalStops<T>& stops)
-    {
-        std::unique_ptr<Expression> get = makeGet(type::Number, property);
-        ParseResult e(std::make_unique<Step>(valueTypeToExpressionType<T>(),
-                                             std::move(get),
-                                             convertStops(stops.stops)));
-        assert(e);
-        return std::move(*e);
-    }
-    
-    template <typename T>
-    static std::unique_ptr<Expression> toExpression(const std::string& property,
-                                                  const CategoricalStops<T>& stops)
-    {
-        ParseResult expr = fromCategoricalStops(stops.stops, property);
-        assert(expr);
-        return std::move(*expr);
-    }
-
-    // interpolatable zoom curve
-    template <typename T>
-    static typename std::enable_if_t<util::Interpolatable<T>::value,
-    ParseResult> makeZoomCurve(std::map<double, std::unique_ptr<Expression>> stops) {
-        ParsingContext ctx;
-        return createInterpolate(valueTypeToExpressionType<T>(),
-                                 ExponentialInterpolator(1.0),
-                                 makeZoom(),
-                                 std::move(stops),
-                                 ctx);
-    }
-    
-    // non-interpolatable zoom curve
-    template <typename T>
-    static typename std::enable_if_t<!util::Interpolatable<T>::value,
-    ParseResult> makeZoomCurve(std::map<double, std::unique_ptr<Expression>> stops) {
-        return ParseResult(std::make_unique<Step>(valueTypeToExpressionType<T>(), makeZoom(), std::move(stops)));
-    }
-
-    template <typename T>
-    static std::unique_ptr<Expression> toExpression(const std::string& property,
-                                                  const CompositeExponentialStops<T>& stops)
-    {
-        ParsingContext ctx;
-
-        std::map<double, std::unique_ptr<Expression>> outerStops;
-        for (const std::pair<float, std::map<float, T>>& stop : stops.stops) {
-            ParseResult innerInterpolate = createInterpolate(valueTypeToExpressionType<T>(),
-                                                             ExponentialInterpolator(stops.base),
-                                                             makeGet(type::Number, property),
-                                                             convertStops(stop.second),
-                                                             ctx);
-            assert(innerInterpolate);
-            outerStops.emplace(stop.first, std::move(*innerInterpolate));
-        }
-        
-        ParseResult zoomCurve = makeZoomCurve<T>(std::move(outerStops));
-        assert(zoomCurve);
-        return std::move(*zoomCurve);
-    }
-    
-    template <typename T>
-    static std::unique_ptr<Expression> toExpression(const std::string& property,
-                                                  const CompositeIntervalStops<T>& stops)
-    {
-        std::map<double, std::unique_ptr<Expression>> outerStops;
-        for (const std::pair<float, std::map<float, T>>& stop : stops.stops) {
-            std::unique_ptr<Expression> get = makeGet(type::Number, property);
-            ParseResult innerInterpolate(std::make_unique<Step>(valueTypeToExpressionType<T>(),
-                                                                std::move(get),
-                                                                convertStops(stop.second)));
-            assert(innerInterpolate);
-            outerStops.emplace(stop.first, std::move(*innerInterpolate));
-        }
-
-        ParseResult zoomCurve = makeZoomCurve<T>(std::move(outerStops));
-        assert(zoomCurve);
-        return std::move(*zoomCurve);
-    }
-    
-    template <typename T>
-    static std::unique_ptr<Expression> toExpression(const std::string& property,
-                                                  const CompositeCategoricalStops<T>& stops)
-    {
-        std::map<double, std::unique_ptr<Expression>> outerStops;
-        for (const std::pair<float, std::map<CategoricalValue, T>>& stop : stops.stops) {
-            ParseResult innerInterpolate = fromCategoricalStops(stop.second, property);
-            assert(innerInterpolate);
-            outerStops.emplace(stop.first, std::move(*innerInterpolate));
-        }
-        
-        ParseResult zoomCurve = makeZoomCurve<T>(std::move(outerStops));
-        assert(zoomCurve);
-        return std::move(*zoomCurve);
-    }
-
-    template <typename T>
-    static std::unique_ptr<Expression> toExpression(const std::string& property,
-                                                    const IdentityStops<T>&)
-    {
-        return fromIdentityFunction(property, expression::valueTypeToExpressionType<T>());
-    }
-
-private:
-    static std::unique_ptr<Expression> fromIdentityFunction(const std::string& property, type::Type type);
-};
-
-} // namespace expression
-} // namespace style
-} // namespace mbgl
diff --git a/include/mbgl/style/function/exponential_stops.hpp b/include/mbgl/style/function/exponential_stops.hpp
deleted file mode 100644
index b3866c4059..0000000000
--- a/include/mbgl/style/function/exponential_stops.hpp
+++ /dev/null
@@ -1,56 +0,0 @@
-#pragma once
-
-#include <mbgl/util/feature.hpp>
-#include <mbgl/util/interpolate.hpp>
-
-#include <map>
-
-namespace mbgl {
-namespace style {
-
-template <class T>
-class ExponentialStops {
-public:
-    using Stops = std::map<float, T>;
-
-    Stops stops;
-    float base = 1.0f;
-
-    ExponentialStops() = default;
-    ExponentialStops(Stops stops_, float base_ = 1.0f)
-        : stops(std::move(stops_)),
-          base(base_) {
-    }
-
-    optional<T> evaluate(float z) const {
-        if (stops.empty()) {
-            return {};
-        }
-
-        auto it = stops.upper_bound(z);
-        if (it == stops.end()) {
-            return stops.rbegin()->second;
-        } else if (it == stops.begin()) {
-            return stops.begin()->second;
-        } else {
-            return util::interpolate(std::prev(it)->second, it->second,
-                util::interpolationFactor(base, { std::prev(it)->first, it->first }, z));
-        }
-    }
-
-    optional<T> evaluate(const Value& value) const {
-        optional<float> z = numericValue<float>(value);
-        if (!z) {
-            return {};
-        }
-        return evaluate(*z);
-    }
-
-    friend bool operator==(const ExponentialStops& lhs,
-                           const ExponentialStops& rhs) {
-        return lhs.stops == rhs.stops && lhs.base == rhs.base;
-    }
-};
-
-} // namespace style
-} // namespace mbgl
diff --git a/include/mbgl/style/function/identity_stops.hpp b/include/mbgl/style/function/identity_stops.hpp
deleted file mode 100644
index 741ebbbe0c..0000000000
--- a/include/mbgl/style/function/identity_stops.hpp
+++ /dev/null
@@ -1,20 +0,0 @@
-#pragma once
-
-#include <mbgl/util/feature.hpp>
-
-namespace mbgl {
-namespace style {
-
-template <class T>
-class IdentityStops {
-public:
-    optional<T> evaluate(const Value&) const;
-
-    friend bool operator==(const IdentityStops&,
-                           const IdentityStops&) {
-        return true;
-    }
-};
-
-} // namespace style
-} // namespace mbgl
diff --git a/include/mbgl/style/function/interval_stops.hpp b/include/mbgl/style/function/interval_stops.hpp
deleted file mode 100644
index 45e2dc6f2e..0000000000
--- a/include/mbgl/style/function/interval_stops.hpp
+++ /dev/null
@@ -1,51 +0,0 @@
-#pragma once
-
-#include <mbgl/util/feature.hpp>
-
-#include <map>
-
-namespace mbgl {
-namespace style {
-
-template <class T>
-class IntervalStops {
-public:
-    using Stops = std::map<float, T>;
-    Stops stops;
-
-    IntervalStops() = default;
-    IntervalStops(Stops stops_)
-        : stops(std::move(stops_)) {
-    }
-
-    optional<T> evaluate(float z) const {
-        if (stops.empty()) {
-            return {};
-        }
-
-        auto it = stops.upper_bound(z);
-        if (it == stops.end()) {
-            return stops.rbegin()->second;
-        } else if (it == stops.begin()) {
-            return stops.begin()->second;
-        } else {
-            return std::prev(it)->second;
-        }
-    }
-
-    optional<T> evaluate(const Value& value) const {
-        optional<float> z = numericValue<float>(value);
-        if (!z) {
-            return {};
-        }
-        return evaluate(*z);
-    }
-
-    friend bool operator==(const IntervalStops& lhs,
-                           const IntervalStops& rhs) {
-        return lhs.stops == rhs.stops;
-    }
-};
-
-} // namespace style
-} // namespace mbgl