# 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 +] trace
               • 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 left, then a
    bullet symbol,``•``, to represent the current locus of processing, then
    the pending expression to the right.
    '''
    # (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
    from ..joy import joy
    from ..library import inscribe, FunctionWrapper

    @inscribe
    @FunctionWrapper
    def trace(stack, expression, dictionary):
    	'''Evaluate a Joy expression on a stack and print a trace.

    	This function is just like the `i` combinator but it also prints a
    	trace of the evaluation

    	:param stack stack: The stack.
    	:param stack expression: The expression to evaluate.
    	:param dict dictionary: A ``dict`` mapping names to Joy functions.
    	:rtype: (stack, (), dictionary)

    	'''
    	tp = TracePrinter()
    	quote, stack = stack
    	try:
    		s, _, d = joy(stack, quote, dictionary, tp.viewer)
    	except:
    		tp.print_()
    		print('-' * 73)
    		raise
    	else:
    		tp.print_()
    	return s, expression, d

    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.')