Malformed Description field: should contain one or more complete sentences.
blockMessage : <anonymous>: no visible global function definition for
  'head'
blockMessage: no visible global function definition for 'head'
blockMessage: no visible global function definition for 'tail'
Undefined global functions or variables:
  head tail
Consider adding
  importFrom("utils", "head", "tail")
to your NAMESPACE file.
Malformed Description field: should contain one or more complete sentences.
blockMessage : <anonymous>: no visible global function definition for
  ‘head’
blockMessage: no visible global function definition for ‘head’
blockMessage: no visible global function definition for ‘tail’
Undefined global functions or variables:
  head tail
Consider adding
  importFrom("utils", "head", "tail")
to your NAMESPACE file.
Malformed Description field: should contain one or more complete sentences.
blockMessage : <anonymous>: no visible global function definition for
  ‘head’
blockMessage: no visible global function definition for ‘head’
blockMessage: no visible global function definition for ‘tail’
Undefined global functions or variables:
  head tail
Consider adding
  importFrom("utils", "head", "tail")
to your NAMESPACE file.
Malformed Description field: should contain one or more complete sentences.
blockMessage : <anonymous>: no visible global function definition for
  ‘head’
blockMessage: no visible global function definition for ‘head’
blockMessage: no visible global function definition for ‘tail’
Undefined global functions or variables:
  head tail
Consider adding
  importFrom("utils", "head", "tail")
to your NAMESPACE file.
Malformed Description field: should contain one or more complete sentences.
blockMessage : <anonymous>: no visible global function definition for
  'head'
blockMessage: no visible global function definition for 'head'
blockMessage: no visible global function definition for 'tail'
Undefined global functions or variables:
  head tail
Consider adding
  importFrom("utils", "head", "tail")
to your NAMESPACE file.
Malformed Description field: should contain one or more complete sentences.
blockMessage : <anonymous>: no visible global function definition for
  ‘head’
blockMessage: no visible global function definition for ‘head’
blockMessage: no visible global function definition for ‘tail’
Undefined global functions or variables:
  head tail
Consider adding
  importFrom("utils", "head", "tail")
to your NAMESPACE file.
Malformed Description field: should contain one or more complete sentences.
blockMessage : <anonymous>: no visible global function definition for
  ‘head’
blockMessage: no visible global function definition for ‘head’
blockMessage: no visible global function definition for ‘tail’
Undefined global functions or variables:
  head tail
Consider adding
  importFrom("utils", "head", "tail")
to your NAMESPACE file.
Malformed Description field: should contain one or more complete sentences.
blockMessage : <anonymous>: no visible global function definition for
  ‘head’
blockMessage: no visible global function definition for ‘head’
blockMessage: no visible global function definition for ‘tail’
Undefined global functions or variables:
  head tail
Consider adding
  importFrom("utils", "head", "tail")
to your NAMESPACE file.
Malformed Description field: should contain one or more complete sentences.
blockMessage : <anonymous>: no visible global function definition for
  ‘head’
blockMessage: no visible global function definition for ‘head’
blockMessage: no visible global function definition for ‘tail’
Undefined global functions or variables:
  head tail
Consider adding
  importFrom("utils", "head", "tail")
to your NAMESPACE file.
Malformed Description field: should contain one or more complete sentences.
blockMessage : <anonymous>: no visible global function definition for
  'head'
blockMessage: no visible global function definition for 'head'
blockMessage: no visible global function definition for 'tail'
Undefined global functions or variables:
  head tail
Consider adding
  importFrom("utils", "head", "tail")
to your NAMESPACE file.
Malformed Description field: should contain one or more complete sentences.
blockMessage : <anonymous>: no visible global function definition for
  ‘head’
blockMessage: no visible global function definition for ‘head’
blockMessage: no visible global function definition for ‘tail’
Undefined global functions or variables:
  head tail
Consider adding
  importFrom("utils", "head", "tail")
to your NAMESPACE file.
Malformed Description field: should contain one or more complete sentences.
blockMessage : <anonymous>: no visible global function definition for
  ‘head’
blockMessage: no visible global function definition for ‘head’
blockMessage: no visible global function definition for ‘tail’
Undefined global functions or variables:
  head tail
Consider adding
  importFrom("utils", "head", "tail")
to your NAMESPACE file.
Malformed Description field: should contain one or more complete sentences.
blockMessage : <anonymous>: no visible global function definition for
  'head'
blockMessage: no visible global function definition for 'head'
blockMessage: no visible global function definition for 'tail'
Undefined global functions or variables:
  head tail
Consider adding
  importFrom("utils", "head", "tail")
to your NAMESPACE file.