Support 'each' transformation.

src/index.ts

@@ -94,15 +94,20 @@ function applyLodashArgs(path, object, args) {
 
   for (const op in args) {
     const arg = args[op];
-    const type = transformationToType[op];
+
+    const type = (op === 'each' ? 'Array' : transformationToType[op]);
     const actualType = object.constructor.name;
     if (type !== actualType) {
       const pathStr = path.join('.');
       throw Error(
         `${pathStr}: "${op}" transformation expect "${type}" but got "${actualType}"`
       );
     }
-    object = transformations[type][op](object, arg);
+
+    if (op === 'each')
+      object = object.map((item, idx) => applyLodashArgs(path.concat(idx), item, arg));
+    else
+      object = transformations[type][op](object, arg);
   }
   return object;
 }

src/lodash_idl.ts

@@ -9,6 +9,7 @@ enum DummyArgument {
 directive @_(
   map: Path
   keyBy: Path
+  each: LodashOperations
 
   # Creates an array of elements split into groups the length of size.
   # If array can't be split evenly, the final chunk will be the remaining elements.
@@ -81,4 +82,81 @@ directive @_(
   # Creates an array of the own enumerable string keyed property values of object.
   values: DummyArgument
 ) on FIELD | QUERY
+
+input LodashOperations {
+  map: Path
+  keyBy: Path
+  each: LodashOperations
+
+  # Creates an array of elements split into groups the length of size.
+  # If array can't be split evenly, the final chunk will be the remaining elements.
+  chunk: Int
+
+  # Creates a slice of array with n elements dropped from the beginning.
+  drop: Int
+
+  # Creates a slice of array with n elements dropped from the end.
+  dropRight: Int
+
+  # Creates a slice of array with n elements taken from the beginning.
+  take: Int
+
+  # Creates a slice of array with n elements taken from the end.
+  takeRight: Int
+
+  # Recursively flatten array up to depth times.
+  flattenDepth: Int
+
+  # The inverse of \`toPairs\`; this method returns an object composed from key-value
+  # pairs.
+  fromPairs: DummyArgument
+
+  # Gets the element at index n of array. If n is negative, the nth element from
+  # the end is returned.
+  nth: Int
+
+  # Reverses array so that the first element becomes the last, the second element
+  # becomes the second to last, and so on.
+  reverse: DummyArgument
+
+  # Creates a duplicate-free version of an array, in which only the first occurrence
+  # of each element is kept. The order of result values is determined by the order
+  # they occur in the array.
+  uniq: DummyArgument
+
+  uniqBy: Path
+
+  countBy: Path
+  filter: JSON
+  reject: JSON
+  groupBy: Path
+  sortBy: [Path!]
+
+  minBy: Path
+  maxBy: Path
+  meanBy: Path
+  sumBy: Path
+
+  # Converts all elements in array into a string separated by separator.
+  join: String
+
+  get: Path
+  mapValues: Path
+
+  # Creates an array of values corresponding to paths of object.
+  at: [Path!]
+  # Creates an array of own enumerable string keyed-value pairs for object.
+  toPairs: DummyArgument
+
+  # Creates an object composed of the inverted keys and values of object.
+  # If object contains duplicate values, subsequent values overwrite property
+  # assignments of previous values.
+  invert: DummyArgument
+
+  invertBy: Path
+  # Creates an array of the own enumerable property names of object.
+  keys: DummyArgument
+  # Creates an array of the own enumerable string keyed property values of object.
+  values: DummyArgument
+}
 `;