const HMP = require('hindley-milner-parser-js');
HMP.parse('hello :: Foo a => a -> String');
{
  name: 'hello',
  constraints: [
    {typeclass: 'Foo', typevar: 'a'}],
  type:
    {type: 'function', text: '', children: [
      {type: 'typevar', text: 'a', children: []},
      {type: 'typeConstructor', text: 'String', children: []}]};