# Source code for joy.utils.pretty_print

    # -*- coding: utf-8 -*-
    #
    #    Copyright © 2016 Simon Forman
    #
    #    This file is part of Thun.
    #
    #    Thun is free software: you can redistribute it and/or modify
    #    it under the terms of the GNU General Public License as published by
    #    the Free Software Foundation, either version 3 of the License, or
    #    (at your option) any later version.
    #
    #    Thun is distributed in the hope that it will be useful,
    #    but WITHOUT ANY WARRANTY; without even the implied warranty of
    #    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    #    GNU General Public License for more details.
    #
    #    You should have received a copy of the GNU General Public License
    #    along with Thun.  If not see <http://www.gnu.org/licenses/>.
    #
    '''
    Pretty printing support, e.g.::

        Joy? 23 18 * 99 +
               . 23 18 mul 99 add
            23 . 18 mul 99 add
         23 18 . mul 99 add
           414 . 99 add
        414 99 . add
           513 .

        513 <-top

        joy?

    On each line the stack is printed with the top to the right, then a ``.`` to
    represent the current locus of processing, then the pending expression to the
    left.

    '''
    # (Kinda clunky and hacky.  This should be swapped out in favor of much
    # smarter stuff.)
    from __future__ import print_function
    from builtins import object
    from traceback import print_exc
    from .stack import expression_to_string, stack_to_string

    class TracePrinter(object):
    	'''
    	This is what does the formatting.  You instantiate it and pass the ``viewer()``
    	method to the :py:func:`joy.joy.joy` function, then print it to see the
    	trace.
    	'''

    	def __init__(self):
    		self.history = []

    	def viewer(self, stack, expression):
    		'''
    		Record the current stack and expression in the TracePrinter's history.
    		Pass this method as the ``viewer`` argument to the :py:func:`joy.joy.joy` function.

    		:param stack quote: A stack.
    		:param stack expression: A stack.
    		'''
    		self.history.append((stack, expression))

    	def __str__(self):
    		return '\n'.join(self.go())

    	def go(self):
    		'''
    		Return a list of strings, one for each entry in the history, prefixed
    		with enough spaces to align all the interpreter dots.

    		This method is called internally by the ``__str__()`` method.

    		:rtype: list(str)
    		'''
    		max_stack_length = 0
    		lines = []
    		for stack, expression in self.history:
    			stack = stack_to_string(stack)
    			expression = expression_to_string(expression)
    			n = len(stack)
    			if n > max_stack_length:
    				max_stack_length = n
    			lines.append((n, '%s . %s' % (stack, expression)))
    		return [  # Prefix spaces to line up '.'s.
    			(' ' * (max_stack_length - length) + line)
    			for length, line in lines
    			]

    	def print_(self):
    		try:
    			print(self)
    		except:
    			print_exc()
    			print('Exception while printing viewer.')