5 files changed, 3385 insertions, 0 deletions

diff --git a/src/Mapbox/Expression.elm b/src/Mapbox/Expression.elm
new file mode 100644
index 0000000..6a9d9f7
--- /dev/null
+++ b/src/Mapbox/Expression.elm
@@ -0,0 +1,1390 @@
+module Mapbox.Expression
+    exposing
+        ( Expression
+        , DataExpression
+        , CameraExpression
+        , encode
+        , Color
+        , Object
+        , Collator
+        , defaultCollator
+        , true
+        , false
+        , bool
+        , int
+        , float
+        , str
+        , rgba
+        , floats
+        , strings
+        , object
+        , collator
+        , assertArray
+        , assertArrayOfStrings
+        , assertArrayOfFloats
+        , assertArrayOfBools
+        , assertBool
+        , assertFloat
+        , assertObject
+        , assertString
+        , toBool
+        , toColor
+        , toFloat
+        , toString
+        , typeof
+        , at
+        , get
+        , has
+        , count
+        , length
+        , geometryType
+        , id
+        , properties
+        , getProperty
+        , hasProperty
+        , isEqual
+        , notEqual
+        , lessThan
+        , lessThanOrEqual
+        , greaterThan
+        , greaterThanOrEqual
+        , isEqualWithCollator
+        , notEqualWithCollator
+        , lessThanWithCollator
+        , lessThanOrEqualWithCollator
+        , greaterThanWithCollator
+        , greaterThanOrEqualWithCollator
+        , not
+        , all
+        , any
+        , ifElse
+        , conditionally
+        , matchesStr
+        , matchesFloat
+        , coallesce
+        , interpolate
+        , Interpolation(..)
+        , step
+        , append
+        , downcase
+        , upcase
+        , isSupportedScript
+        , resolvedLocale
+        , makeRGBColor
+        , makeRGBAColor
+        , rgbaChannels
+        , minus
+        , multiply
+        , divideBy
+        , modBy
+        , plus
+        , raiseBy
+        , sqrt
+        , abs
+        , ceil
+        , floor
+        , round
+        , cos
+        , sin
+        , tan
+        , acos
+        , asin
+        , atan
+        , e
+        , pi
+        , ln
+        , ln2
+        , log10
+        , log2
+        , zoom
+        , heatmapDensity
+        , lineProgress
+        , Anchor(..)
+        , anchorMap
+        , anchorViewport
+        , AnchorAuto
+        , anchorAutoMap
+        , anchorAutoViewport
+        , anchorAutoAuto
+        , Position
+        , positionCenter
+        , positionLeft
+        , positionRight
+        , positionTop
+        , positionBottom
+        , positionTopLeft
+        , positionTopRight
+        , positionBottomLeft
+        , positionBottomRight
+        , TextFit
+        , textFitNone
+        , textFitWidth
+        , textFitHeight
+        , textFitBoth
+        , LineCap
+        , lineCapButt
+        , lineCapRound
+        , lineCapSquare
+        , LineJoin
+        , lineJoinBevel
+        , lineJoinRound
+        , lineJoinMiter
+        , SymbolPlacement
+        , symbolPlacementPoint
+        , symbolPlacementLine
+        , TextJustify
+        , textJustifyLeft
+        , textJustifyCenter
+        , textJustifyRight
+        , TextTransform
+        , textTransformNone
+        , textTransformUppercase
+        , textTransformLowercase
+        )
+
+{-| Expressions form a little language that can be used to compute values for various layer properties.
+
+It is recommended to import them in the following fashion:
+
+    import Mapbox.Expression as E exposing (str, float, int, true, false)
+
+This way you can use the language without much syntactic fuss and you have easy access to the literals.
+
+**Note**: If you are familiar with the JS version of the style spec,
+we have made a few changes. Argument order has been switched for many functions to support using pipeline style more naturally. Some functions use overloading in the original, these have been renamed to
+not be overloaded. Finally, we have chosen not to represent some parts of the spec that are superflous (especially when used form Elm), namely functions and let-in expressions.
+
+@docs Expression, DataExpression, CameraExpression
+
+@docs encode
+
+
+### Types
+
+All of the types used as expression results are phantom (i.e. they don't have any runtime values but are used purely for compile-time checking). As such we use a mix of standard elm types for their familiarty:
+
+  - `Float`
+  - `String`
+  - `Array`
+  - `Bool`
+
+We introduce the following types:
+
+@docs Color, Object, Collator
+
+(And also a bunch of Enum types, that will be documented in the Enums section).
+
+You can use the following functions to transfer Elm values into the Expression language:
+
+@docs true, false, bool, int, float, str, rgba, floats, strings, object, collator, defaultCollator
+
+In some cases, you will need to force the type system to cooperate.
+The following assertions will force the type and cause a run-time error
+if the type is wrong:
+
+@docs assertArray, assertArrayOfStrings, assertArrayOfFloats, assertArrayOfBools, assertBool, assertFloat, assertObject, assertString
+
+You can also use these functions to explicitly cast to a particular type:
+
+@docs toBool, toColor, toFloat, toString
+
+@docs typeof
+
+
+### Lookup
+
+@docs at, get, has, count, length
+
+
+### Feature data
+
+@docs geometryType, id, properties, getProperty, hasProperty
+
+
+### Decision
+
+The expressions in this section can be used to add conditional logic to your styles.
+
+@docs isEqual, notEqual, lessThan, lessThanOrEqual, greaterThan, greaterThanOrEqual
+
+Strings can be compared with a collator for locale specific comparisons:
+
+@docs isEqualWithCollator, notEqualWithCollator,lessThanWithCollator, lessThanOrEqualWithCollator, greaterThanWithCollator, greaterThanOrEqualWithCollator
+
+Logical operators:
+
+@docs not, all, any
+
+Control flow:
+
+@docs ifElse, conditionally, matchesStr, matchesFloat, coallesce
+
+
+### Ramps, scales, curves
+
+@docs interpolate, Interpolation, step
+
+
+### String
+
+@docs append, downcase, upcase, isSupportedScript, resolvedLocale
+
+
+### Color
+
+@docs makeRGBColor, makeRGBAColor, rgbaChannels
+
+
+### Math
+
+@docs minus, multiply, divideBy, modBy, plus, raiseBy, sqrt, abs, ceil, floor, round, cos, sin, tan, acos, asin, atan, e, pi, ln, ln2, log10, log2
+
+
+### Zoom
+
+@docs zoom
+
+
+### Heatmap
+
+@docs heatmapDensity, lineProgress
+
+
+### Enums
+
+These are required for various layer properties.
+
+@docs Anchor, anchorMap, anchorViewport, AnchorAuto, anchorAutoMap, anchorAutoViewport, anchorAutoAuto, Position, positionCenter, positionLeft, positionRight, positionTop, positionBottom, positionTopLeft, positionTopRight, positionBottomLeft, positionBottomRight, TextFit, textFitNone, textFitWidth, textFitHeight, textFitBoth, LineCap, lineCapButt, lineCapRound, lineCapSquare, LineJoin, lineJoinBevel, lineJoinRound, lineJoinMiter, SymbolPlacement, symbolPlacementPoint, symbolPlacementLine, TextJustify, textJustifyLeft, textJustifyCenter, textJustifyRight, TextTransform, textTransformNone, textTransformUppercase, textTransformLowercase
+
+-}
+
+import Array exposing (Array)
+import Json.Encode exposing (Value)
+
+
+{-| Expressions are zero overhead wrappers over the underlying JSON language that attempt to provide some type safety.
+
+Note however, that while being a strictly typed language, it has slighlty different semantics tham Elm:
+
+  - There is only a single number type. I have denoted it `Float`. You will notice that the `int` function takes an Elm int
+    value and converts it to an `Expression expr Float`.
+  - All values may be `null`. There is no `Maybe` type. You can use the `coallesce` function to handle this.
+  - There is no distinction between `List`, `Array`, and tuples. Hence all collections are labeled as `Array`.
+  - Dictionaries are called `Object`. The keys are always `String`, but the values can be of mixed types. Hence retrieving
+    values from them makes code untyped.
+  - You can force the types of things using the `assert...` functions. This will generate a runtime error if the type doesn't
+    match. This should be necessary only rarely.
+
+The `exprType` can be:
+
+  - `CameraExpression`
+  - `DataExpression`
+  - or a type variable representing either of the above
+
+The intent is to help you not break your style by using a DataExpression (for example) where it isn't supported. However, this isn't entirely foolproof, so some caution is advised.
+
+-}
+type Expression exprType resultType
+    = Expression Value
+
+
+{-| A camera expression is any expression that uses the zoom operator. Such expressions allow the the appearance of a layer
+to change with the map's zoom level. Camera expressions can be used to create the appearance of depth and to control data density.
+
+    zoom
+        |> interpolate Linear
+            [ ( 5, int 1 )
+            , ( 10, int 5 )
+            ]
+        |> Layer.circleRadius
+
+This example uses the `interpolate` operator to define a linear relationship between zoom level and circle size using a set of input-output pairs. In this case, the expression indicates that the circle radius should be 1 pixel when the zoom level is 5 or below, and 5 pixels when the zoom is 10 or above. In between, the radius will be linearly interpolated between 1 and 5 pixels
+
+Camera expressions are allowed anywhere an expression may be used. However, when a camera expression used as the value of a layout or paint property, the `zoom` operator must appear only as the input to an outer `interpolate` or `step` expression
+
+There is an important difference between layout and paint properties in the timing of camera expression evaluation. Paint property camera expressions are re-evaluated whenever the zoom level changes, even fractionally. For example, a paint property camera expression will be re-evaluated continuously as the map moves between zoom levels 4.1 and 4.6. On the other hand, a layout property camera expression is evaluated only at integer zoom levels. It will not be re-evaluated as the zoom changes from 4.1 to 4.6 -- only if it goes above 5 or below 4.
+
+-}
+type CameraExpression
+    = CameraExpression
+
+
+{-| A data expression is any expression that access feature data -- that is, any expression that uses one of the data operators: `getProperty`, `hasProperty` , `id`, `geometryType`, or `properties`. Data expressions allow a feature's properties to determine its appearance. They can be used to differentiate features within the same layer and to create data visualizations.
+
+    makeRGBColor
+        -- red is higher when feature.properties.temperature is higher
+        (getProperty "temperature")
+        -- green is always zero
+        (int 0)
+        -- blue is higher when feature.properties.temperature is lower
+        (getProperty "temperature" |> minus 100)
+        |> Layer.circleColor
+
+This example uses the `getProperty` operator to obtain the temperature value of each feature. That value is used to compute arguments to the `makeRGBColor` operator, defining a color in terms of its red, green, and blue components.
+
+-}
+type DataExpression
+    = DataExpression
+
+
+{-| Turns an expression into JSON
+-}
+encode : Expression exprType a -> Value
+encode (Expression value) =
+    value
+
+
+{-| Represents a mixed-type dictionary where keys are always strings
+-}
+type Object
+    = Object
+
+
+{-| Represents a color value
+-}
+type Color
+    = Color
+
+
+{-| Used for locale sensitive string comparisons.
+-}
+type Collator
+    = Collator
+
+
+
+-- Enums
+
+
+{-| -}
+type Anchor
+    = Map
+    | Viewport
+
+
+{-| -}
+anchorMap : Expression exprType Anchor
+anchorMap =
+    Expression (Json.Encode.string "map")
+
+
+{-| -}
+anchorViewport : Expression exprType Anchor
+anchorViewport =
+    Expression (Json.Encode.string "viewport")
+
+
+{-| -}
+type AnchorAuto
+    = AnchorAuto
+
+
+{-| -}
+anchorAutoMap : Expression exprType AnchorAuto
+anchorAutoMap =
+    Expression (Json.Encode.string "map")
+
+
+{-| -}
+anchorAutoViewport : Expression exprType AnchorAuto
+anchorAutoViewport =
+    Expression (Json.Encode.string "viewport")
+
+
+{-| -}
+anchorAutoAuto : Expression exprType AnchorAuto
+anchorAutoAuto =
+    Expression (Json.Encode.string "auto")
+
+
+{-| -}
+type Position
+    = Position
+
+
+{-| -}
+positionCenter : Expression exprType Position
+positionCenter =
+    Expression (Json.Encode.string "center")
+
+
+{-| -}
+positionLeft : Expression exprType Position
+positionLeft =
+    Expression (Json.Encode.string "left")
+
+
+{-| -}
+positionRight : Expression exprType Position
+positionRight =
+    Expression (Json.Encode.string "right")
+
+
+{-| -}
+positionTop : Expression exprType Position
+positionTop =
+    Expression (Json.Encode.string "top")
+
+
+{-| -}
+positionBottom : Expression exprType Position
+positionBottom =
+    Expression (Json.Encode.string "bottom")
+
+
+{-| -}
+positionTopLeft : Expression exprType Position
+positionTopLeft =
+    Expression (Json.Encode.string "top-left")
+
+
+{-| -}
+positionTopRight : Expression exprType Position
+positionTopRight =
+    Expression (Json.Encode.string "top-right")
+
+
+{-| -}
+positionBottomLeft : Expression exprType Position
+positionBottomLeft =
+    Expression (Json.Encode.string "bottom-left")
+
+
+{-| -}
+positionBottomRight : Expression exprType Position
+positionBottomRight =
+    Expression (Json.Encode.string "bottom-right")
+
+
+{-| -}
+type TextFit
+    = TextFit
+
+
+{-| -}
+textFitNone : Expression exprType TextFit
+textFitNone =
+    Expression (Json.Encode.string "none")
+
+
+{-| -}
+textFitWidth : Expression exprType TextFit
+textFitWidth =
+    Expression (Json.Encode.string "width")
+
+
+{-| -}
+textFitHeight : Expression exprType TextFit
+textFitHeight =
+    Expression (Json.Encode.string "height")
+
+
+{-| -}
+textFitBoth : Expression exprType TextFit
+textFitBoth =
+    Expression (Json.Encode.string "both")
+
+
+{-| -}
+type LineCap
+    = LineCap
+
+
+{-| -}
+lineCapButt : Expression exprType LineCap
+lineCapButt =
+    Expression (Json.Encode.string "butt")
+
+
+{-| -}
+lineCapRound : Expression exprType LineCap
+lineCapRound =
+    Expression (Json.Encode.string "round")
+
+
+{-| -}
+lineCapSquare : Expression exprType LineCap
+lineCapSquare =
+    Expression (Json.Encode.string "square")
+
+
+{-| -}
+type LineJoin
+    = LineJoin
+
+
+{-| -}
+lineJoinBevel : Expression exprType LineJoin
+lineJoinBevel =
+    Expression (Json.Encode.string "bevel")
+
+
+{-| -}
+lineJoinRound : Expression exprType LineJoin
+lineJoinRound =
+    Expression (Json.Encode.string "round")
+
+
+{-| -}
+lineJoinMiter : Expression exprType LineJoin
+lineJoinMiter =
+    Expression (Json.Encode.string "miter")
+
+
+{-| -}
+type SymbolPlacement
+    = SymbolPlacement
+
+
+{-| -}
+symbolPlacementPoint : Expression exprType SymbolPlacement
+symbolPlacementPoint =
+    Expression (Json.Encode.string "point")
+
+
+{-| -}
+symbolPlacementLine : Expression exprType SymbolPlacement
+symbolPlacementLine =
+    Expression (Json.Encode.string "line")
+
+
+{-| -}
+type TextJustify
+    = TextJustify
+
+
+{-| -}
+textJustifyLeft : Expression exprType TextJustify
+textJustifyLeft =
+    Expression (Json.Encode.string "left")
+
+
+{-| -}
+textJustifyCenter : Expression exprType TextJustify
+textJustifyCenter =
+    Expression (Json.Encode.string "center")
+
+
+{-| -}
+textJustifyRight : Expression exprType TextJustify
+textJustifyRight =
+    Expression (Json.Encode.string "right")
+
+
+{-| -}
+type TextTransform
+    = TextTransform
+
+
+{-| -}
+textTransformNone : Expression exprType TextTransform
+textTransformNone =
+    Expression (Json.Encode.string "none")
+
+
+{-| -}
+textTransformUppercase : Expression exprType TextTransform
+textTransformUppercase =
+    Expression (Json.Encode.string "uppercase")
+
+
+{-| -}
+textTransformLowercase : Expression exprType TextTransform
+textTransformLowercase =
+    Expression (Json.Encode.string "lowercase")
+
+
+
+-- literals
+
+
+{-| -}
+rgba : Float -> Float -> Float -> Float -> Expression exprType Color
+rgba r g b a =
+    Expression (Json.Encode.string ("rgba" ++ Basics.toString ( r, g, b, a )))
+
+
+{-| -}
+str : String -> Expression exprType String
+str s =
+    Expression (Json.Encode.string s)
+
+
+{-| -}
+bool : Bool -> Expression exprType Bool
+bool b =
+    Expression (Json.Encode.bool b)
+
+
+{-| -}
+true : Expression exprType Bool
+true =
+    bool True
+
+
+{-| -}
+false : Expression exprType Bool
+false =
+    bool False
+
+
+{-| -}
+int : Int -> Expression exprType Float
+int number =
+    Expression (Json.Encode.int number)
+
+
+{-| -}
+float : Float -> Expression exprType Float
+float number =
+    Expression (Json.Encode.float number)
+
+
+{-| -}
+floats : List Float -> Expression exprType (Array Float)
+floats =
+    List.map float >> list
+
+
+{-| -}
+strings : List String -> Expression exprType (Array String)
+strings =
+    List.map str >> list
+
+
+list : List (Expression exprType a) -> Expression exprType (Array a)
+list =
+    List.map encode >> Json.Encode.list >> Expression >> call1 "literal"
+
+
+{-| Returns a `Collator` for use in locale-dependent comparison operations. The first argument specifies if the comparison should be case sensitive. The second specifies if it is diacritic sensitive. The final locale argument specifies the IETF language tag of the locale to use.
+-}
+collator : Expression e1 Bool -> Expression e2 Bool -> Expression e3 String -> Expression e4 Collator
+collator (Expression caseSensitive) (Expression diacriticSensitive) (Expression locale) =
+    Expression
+        (Json.Encode.list
+            (Json.Encode.string "collator"
+                :: [ Json.Encode.object
+                        [ ( "case-sensitive", caseSensitive )
+                        , ( "diacritic-sensitive", diacriticSensitive )
+                        , ( "locale", locale )
+                        ]
+                   ]
+            )
+        )
+
+
+{-| Returns a `Collator` with the default locale (which depends on the system running the code), which is not sensitive to case nor diacritic.
+-}
+defaultCollator : Expression exprType Collator
+defaultCollator =
+    call0 "collator"
+
+
+{-| Takes a list of key value pairs. The values are JSON Values,
+therefore allowing for mixed types.
+-}
+object : List ( String, Value ) -> Expression exprType Object
+object =
+    Json.Encode.object >> Expression >> call1 "literal"
+
+
+
+-- Type Functions
+
+
+{-| -}
+assertArray : Expression exprType any -> Expression exprType (Array any)
+assertArray =
+    call1 "array"
+
+
+{-| -}
+assertArrayOfStrings : Expression exprType any -> Expression exprType (Array String)
+assertArrayOfStrings =
+    call2 "array" (str "string")
+
+
+{-| -}
+assertArrayOfFloats : Expression exprType any -> Expression exprType (Array Float)
+assertArrayOfFloats =
+    call2 "array" (str "number")
+
+
+{-| -}
+assertArrayOfBools : Expression exprType any -> Expression exprType (Array Bool)
+assertArrayOfBools =
+    call2 "array" (str "boolean")
+
+
+{-| -}
+assertBool : Expression exprType any -> Expression exprType Bool
+assertBool =
+    call1 "boolean"
+
+
+
+-- assertAtLeastOneBool : List (Expression exprType any) -> Expression exprType Bool
+-- assertAtLeastOneBool =
+--     call "boolean"
+
+
+{-| -}
+assertFloat : Expression exprType any -> Expression exprType Float
+assertFloat =
+    call1 "number"
+
+
+{-| -}
+assertObject : Expression exprType any -> Expression exprType Object
+assertObject =
+    call1 "object"
+
+
+{-| -}
+assertString : Expression exprType any -> Expression exprType String
+assertString =
+    call1 "string"
+
+
+{-| Converts the input value to a boolean. The result is false when then input is an empty string, 0, false, null, or NaN; otherwise it is true.
+-}
+toBool : Expression exprType any -> Expression exprType Bool
+toBool =
+    call1 "to-boolean"
+
+
+{-| Converts the input value to a color. If it can't be converted, the falback value will be used.
+
+    input
+      |> toColor (rgba 0 0 0 1) -- fallback color
+
+-}
+toColor : Expression exprType2 Color -> Expression exprType any -> Expression exprType Color
+toColor fallback input =
+    call2 "to-color" input fallback
+
+
+{-| Converts the input value to a number, if possible. If the input is null or false, the result is 0. If the input is true, the result is 1. If the input is a string, it is converted to a number as specified by the ["ToNumber Applied to the String Type" algorithm of the ECMAScript Language Specification](https://tc39.github.io/ecma262/#sec-tonumber-applied-to-the-string-type). If this fails, the fallback value is used.
+
+    input
+      |> toFloat 0 -- fallback
+
+-}
+toFloat : Float -> Expression exprType any -> Expression exprType Float
+toFloat fallback input =
+    call2 "to-number" input (float fallback)
+
+
+{-| Converts the input value to a string. If the input is `null`, the result is `""`. If the input is a boolean, the result is `"true"` or `"false"`. If the input is a number, it is converted to a string as specified by the ["NumberToString" algorithm](https://tc39.github.io/ecma262/#sec-tostring-applied-to-the-number-type) of the ECMAScript Language Specification. If the input is a color, it is converted to a string of the form `"rgba(r,g,b,a)"`, where r, g, and b are numerals ranging from 0 to 255, and a ranges from 0 to 1. Otherwise, the input is converted to a string in the format specified by the [`JSON.stringify`](https://tc39.github.io/ecma262/#sec-json.stringify) function of the ECMAScript Language Specification.
+-}
+toString : Expression exprType any -> Expression exprType String
+toString =
+    call1 "to-string"
+
+
+{-| Returns a string describing the type of the given value.
+-}
+typeof : Expression exprType any -> Expression exprType String
+typeof =
+    call1 "typeof"
+
+
+
+-- Expressions
+
+
+call0 n =
+    call n []
+
+
+call1 n (Expression a) =
+    call n [ a ]
+
+
+call2 n (Expression a) (Expression b) =
+    call n [ a, b ]
+
+
+call3 n (Expression a) (Expression b) (Expression c) =
+    call n [ a, b, c ]
+
+
+call4 n (Expression a) (Expression b) (Expression c) (Expression d) =
+    call n [ a, b, c, d ]
+
+
+calln n expressions =
+    call n (List.map encode expressions)
+
+
+call name args =
+    Expression (Json.Encode.list (Json.Encode.string name :: args))
+
+
+{-| Gets the feature's geometry type: Point, MultiPoint, LineString, MultiLineString, Polygon, MultiPolygon.
+-}
+geometryType : Expression DataExpression String
+geometryType =
+    call0 "geometry-type"
+
+
+{-| Gets the feature's id, if it has one.
+-}
+id : Expression DataExpression any
+id =
+    call0 "id"
+
+
+{-| Gets the feature properties object. Note that in some cases, it may be more efficient to use `getProperty (str "property-name")` directly.
+-}
+properties : Expression DataExpression Object
+properties =
+    call0 "properties"
+
+
+{-| Retrieves an item from an array.
+-}
+at : Expression exprType1 Float -> Expression exprType2 (Array a) -> Expression exprType2 a
+at =
+    call2 "at"
+
+
+{-| Retrieves a property value from the current feature's properties. Returns null if the requested property is missing.
+-}
+getProperty : Expression exprType String -> Expression DataExpression any
+getProperty =
+    call1 "get"
+
+
+{-| Retrieves a property value from an object. Returns null if the requested property is missing.
+-}
+get : Expression exprType1 String -> Expression exprType2 Object -> Expression exprType2 any
+get =
+    call2 "get"
+
+
+{-| Tests for the presence of an property value in the current feature's properties.
+-}
+hasProperty : Expression exprType String -> Expression DataExpression Bool
+hasProperty =
+    call1 "has"
+
+
+{-| Tests for the presence of an property value in an object.
+-}
+has : Expression exprType1 String -> Expression exprType2 Object -> Expression exprType2 Bool
+has =
+    call2 "has"
+
+
+{-| Gets the length of an array.
+-}
+count : Expression exprType (Array any) -> Expression exprType Float
+count =
+    call1 "length"
+
+
+{-| Gets the length of a string.
+-}
+length : Expression exprType String -> Expression exprType Float
+length =
+    call1 "length"
+
+
+{-| Logical negation. Returns true if the input is false, and false if the input is true.
+-}
+not : Expression exprType Bool -> Expression exprType Bool
+not =
+    call1 "!"
+
+
+{-| Returns true if the input values are not equal, false otherwise.
+-}
+notEqual : Expression exprType1 a -> Expression exprType2 a -> Expression exprType1 Bool
+notEqual =
+    call2 "!="
+
+
+{-| -}
+notEqualWithCollator : Expression exprType1 String -> Expression exprType2 String -> Expression exprType3 Collator -> Expression exprType1 Bool
+notEqualWithCollator =
+    call3 "!="
+
+
+{-| Returns true if the first input is strictly less than the second, false otherwise.
+-}
+lessThan : Expression exprType1 comparable -> Expression exprType2 comparable -> Expression exprType1 Bool
+lessThan =
+    call2 "<"
+
+
+{-| -}
+lessThanWithCollator : Expression exprType1 String -> Expression exprType2 String -> Expression exprType3 Collator -> Expression exprType1 Bool
+lessThanWithCollator =
+    call3 "<"
+
+
+{-| Returns true if the first input is less than or equal to the second, false otherwise.
+-}
+lessThanOrEqual : Expression exprType1 comparable -> Expression exprType2 comparable -> Expression exprType1 Bool
+lessThanOrEqual =
+    call2 "<="
+
+
+{-| -}
+lessThanOrEqualWithCollator : Expression exprType1 String -> Expression exprType2 String -> Expression exprType3 Collator -> Expression exprType1 Bool
+lessThanOrEqualWithCollator =
+    call3 "<="
+
+
+{-| Returns true if the input values are equal, false otherwise.
+-}
+isEqual : Expression exprType1 a -> Expression exprType2 a -> Expression exprType1 Bool
+isEqual =
+    call2 "=="
+
+
+{-| -}
+isEqualWithCollator : Expression exprType1 String -> Expression exprType2 String -> Expression exprType3 Collator -> Expression exprType1 Bool
+isEqualWithCollator =
+    call3 "=="
+
+
+{-| Returns true if the first input is strictly greater than the second, false otherwise.
+-}
+greaterThan : Expression exprType1 comparable -> Expression exprType2 comparable -> Expression exprType1 Bool
+greaterThan =
+    call2 ">"
+
+
+{-| -}
+greaterThanWithCollator : Expression exprType1 String -> Expression exprType2 String -> Expression exprType3 Collator -> Expression exprType1 Bool
+greaterThanWithCollator =
+    call3 ">"
+
+
+{-| Returns true if the first input is greater than or equal to the second, false otherwise.
+-}
+greaterThanOrEqual : Expression exprType1 comparable -> Expression exprType2 comparable -> Expression exprType1 Bool
+greaterThanOrEqual =
+    call2 ">="
+
+
+{-| -}
+greaterThanOrEqualWithCollator : Expression exprType1 String -> Expression exprType2 String -> Expression exprType3 Collator -> Expression exprType1 Bool
+greaterThanOrEqualWithCollator =
+    call3 ">="
+
+
+{-| Returns true if all the inputs are true, false otherwise. The inputs are evaluated in order, and evaluation is short-circuiting: once an input expression evaluates to false, the result is false and no further input expressions are evaluated.
+-}
+all : List (Expression exprType Bool) -> Expression exprType Bool
+all =
+    calln "all"
+
+
+{-| Returns true if any of the inputs are true, false otherwise. The inputs are evaluated in order, and evaluation is short-circuiting: once an input expression evaluates to true, the result is true and no further input expressions are evaluated.
+-}
+any : List (Expression exprType Bool) -> Expression exprType Bool
+any =
+    calln "any"
+
+
+{-| Evaluates each expression in turn until the first non-null value is obtained, and returns that value.
+-}
+coallesce : List (Expression exprType outputType) -> Expression exprType outputType
+coallesce =
+    calln "coallesce"
+
+
+{-| The ternary operator:
+
+    Layer.iconImage <|
+      ifElse
+        (greaterThan (getProperty (str "size")) (float 30))
+        (str "hospital-32")
+        (str "clinic-32")
+
+-}
+ifElse : Expression exprType1 Bool -> Expression exprType2 output -> Expression exprType3 output -> Expression exprType1 output
+ifElse =
+    call3 "case"
+
+
+{-| Selects the first output whose condition evaluates to `true`
+-}
+conditionally : List ( Expression exprType1 Bool, Expression exprType2 output ) -> Expression exprType2 output -> Expression exprType1 output
+conditionally vals (Expression default) =
+    call "case" (List.concatMap (\( Expression cond, Expression res ) -> [ cond, res ]) vals ++ [ default ])
+
+
+{-| Selects the output whose label value matches the input value, or the fallback value if no match is found.
+
+    getProperty (str "type")
+      |> matchesStr
+          [ ("hospital", str "icon-hospital")
+          , ("clinic", str "icon-medical")
+          ]
+          (str "icon-generic") -- fallback value
+      |> Layer.iconImage
+
+-}
+matchesStr : List ( String, Expression exprType2 output ) -> Expression exprType1 output -> Expression exprType3 String -> Expression exprType3 output
+matchesStr options (Expression default) (Expression input) =
+    let
+        properOptions =
+            List.concatMap (\( label, Expression output ) -> [ Json.Encode.string label, output ]) options
+    in
+        call "match" (input :: properOptions ++ [ default ])
+
+
+{-| Selects the output whose label value matches the input value, or the fallback value if no match is found.
+
+    getProperty (str "size")
+      |> matchesStr
+          [ (1, str "icon-hospital")
+          , (2, str "icon-medical")
+          ]
+          (str "icon-generic") -- fallback value
+      |> Layer.iconImage
+
+-}
+matchesFloat : List ( Float, Expression exprType2 output ) -> Expression exprType1 output -> Expression exprType3 Float -> Expression exprType3 output
+matchesFloat options (Expression default) (Expression input) =
+    let
+        properOptions =
+            List.concatMap (\( label, Expression output ) -> [ Json.Encode.float label, output ]) options
+    in
+        call "match" (input :: properOptions ++ [ default ])
+
+
+{-| Interpolation types:
+
+  - `Linear`: interpolates linearly between the pair of stops just less than and just greater than the input.
+  - `Exponential base`: interpolates exponentially between the stops just less than and just greater than the input. `base` controls the rate at which the output increases: higher values make the output increase more towards the high end of the range. With values close to 1 the output increases linearly.
+  - `CubicBezier (x1, y1)  (x2, y2)`: interpolates using the cubic bezier curve defined by the given control points.
+
+-}
+type Interpolation
+    = Linear
+    | Exponential Float
+    | CubicBezier ( Float, Float ) ( Float, Float )
+
+
+encodeInterpolation interpolation =
+    case interpolation of
+        Linear ->
+            call0 "linear"
+
+        Exponential base ->
+            call "exponential" [ Json.Encode.float base ]
+
+        CubicBezier ( x1, y1 ) ( x2, y2 ) ->
+            call "cubic-bezier" [ Json.Encode.float x1, Json.Encode.float y1, Json.Encode.float x2, Json.Encode.float y2 ]
+
+
+{-| Produces continuous, smooth results by interpolating between pairs of input and output values ("stops"). The output type must be `Float`, `Array Float`, or `Color`.
+
+    zoom
+        |> interpolate Linear
+            [ ( 5, int 1 )
+            , ( 10, int 5 )
+            ]
+        |> Layer.circleRadius
+
+-}
+interpolate : Interpolation -> List ( Float, Expression exprType2 outputType ) -> Expression exprType1 Float -> Expression exprType1 outputType
+interpolate interpolation stops (Expression input) =
+    call "interpolate" <| (encodeInterpolation interpolation |> encode) :: input :: List.concatMap (\( stop, Expression res ) -> [ Json.Encode.float stop, res ]) stops
+
+
+{-| Produces discrete, stepped results by evaluating a piecewise-constant function defined by pairs of input and output values ("stops"). Stop inputs must be Floats in strictly ascending order. Returns the output value of the stop just less than the input, or the first input if the input is less than the first stop.
+
+    zoom
+        |> step (int 1)
+            [ ( 5, int 3 )
+            , ( 10, int 5 )
+            ]
+        |> Layer.circleRadius
+
+-}
+step : Expression exprType2 Float -> List ( Float, Expression exprType1 output ) -> Expression exprType1 output -> Expression exprType2 output
+step (Expression default) stops (Expression input) =
+    call "step" <| input :: default :: List.concatMap (\( stop, Expression res ) -> [ Json.Encode.float stop, res ]) stops
+
+
+{-| Returns a string consisting of the concatenation of the inputs.
+
+Argument order designed for pipelines:
+
+    a |> append b --> a ++ b
+
+-}
+append : Expression exprType String -> Expression exprType String -> Expression exprType String
+append a b =
+    call2 "concat" b a
+
+
+{-| Returns the input string converted to lowercase. Follows the Unicode Default Case Conversion algorithm and the locale-insensitive case mappings in the Unicode Character Database.
+-}
+downcase : Expression exprType String -> Expression exprType String
+downcase =
+    call1 "downcase"
+
+
+{-| Returns true if the input string is expected to render legibly. Returns f