implement hindley-milner by skynet

hm.py

# Define a set of basic types
INTEGER = 'INTEGER'
BOOLEAN = 'BOOLEAN'
FUNCTION = 'FUNCTION'

# Define a class for type variables
class TypeVar:
  def __init__(self, name):
    self.name = name
  
  def __repr__(self):
    return self.name

# Define a class for type constraints
class Constraint:
  def __init__(self, left, right):
    self.left = left
    self.right = right

# Define a function for generating fresh type variables
def fresh_type_var(name_hint):
  return TypeVar(name_hint)

# Define a function for inferring the types of expressions
def infer_type(expr, constraints):
  if isinstance(expr, int):
    return INTEGER, constraints
  elif isinstance(expr, bool):
    return BOOLEAN, constraints
  elif isinstance(expr, Function):
    arg_type = fresh_type_var('arg')
    return_type = fresh_type_var('return')
    constraints.append(Constraint(expr.arg_type, arg_type))
    constraints.append(Constraint(expr.return_type, return_type))
    return FUNCTION, constraints
  else:
    raise ValueError(f'Unrecognized expression {expr}')

# Define a function for solving type constraints
def solve(constraints):
  substitution = {}
  for constraint in constraints:
    if isinstance(constraint.left, TypeVar) and constraint.left not in substitution:
      substitution[constraint.left] = constraint.right
  return substitution

# Define a class for functions