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 traceback import print_exc
from .stack import expression_to_string, stack_to_string
from ..joy import joy
from ..library import FunctionWrapper


@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)))
        for i in range(len(lines)):  # Prefix spaces to line up '•'s.
            length, line = lines[i]
            lines[i] =  (' ' * (max_stack_length - length) + line)
        return lines

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