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
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.')