Not all exponential function range values need be numbers

The prior validate.array does the necessary type checking.

Fixes #301

lib/validate/parsed.js

@@ -337,19 +337,6 @@ module.exports = function(style, reference) {
 
         // Ensure all range values are of the correct type
         validate.array(key + '.range', val.range, {type: "array", value: spec});
-
-        // Ensure all range values are of the same type and interpolate-able
-        if (functionType === 'exponential') {
-            var type = typeof_(val.range[0]);
-
-            if (type === 'array') {
-                var length = val.range[0].length;
-                validate.array(key + '.range', val.range, {type: "array", value: {type: "array", value: "number", length: length}});
-            } else {
-                validate.array(key + '.range', val.range, {type: "array", value: "number"});
-            }
-
-        }
     };
 
     validate['function-v7'] = function(key, val, spec) {

test/fixture/functions.input.json

@@ -181,6 +181,20 @@
           "range": [[1,2], [2,4]]
         }
       }
+    },
+    {
+      "id": "13 valid exponential scale with color",
+      "type": "line",
+      "source": "source",
+      "source-layer": "layer",
+      "paint": {
+        "line-color": {
+          "property": "mapbox",
+          "domain": [1, 2],
+          "range": ["#000000", "#FFFFFF"],
+          "base": 1.5
+        }
+      }
     }
   ]
 }

test/fixture/functions.output.json

@@ -3,10 +3,6 @@
     "message": "layers[3].paint.fill-color.range[0]: color expected, boolean found",
     "line": 61
   },
-  {
-    "message": "layers[3].paint.fill-color.range[0]: number expected, boolean found",
-    "line": 61
-  },
   {
     "message": "layers[4].paint.line-width.domain[0]: number expected, boolean found",
     "line": 74