170 lines
4.3 KiB
Python
170 lines
4.3 KiB
Python
# -*- coding: utf-8 -*-
|
|
#
|
|
# Copyright © 2014, 2015, 2017 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/>.
|
|
#
|
|
'''
|
|
When talking about Joy we use the terms "stack", "list", "sequence",
|
|
"quote" and others to mean the same thing: a simple linear datatype that
|
|
permits certain operations such as iterating and pushing and popping
|
|
values from (at least) one end.
|
|
|
|
We use the venerable two-tuple recursive form of sequences where the
|
|
empty tuple () is the empty stack and (head, rest) gives the recursive
|
|
form of a stack with one or more items on it::
|
|
|
|
stack := () | (item, stack)
|
|
|
|
Putting some numbers onto a stack::
|
|
|
|
()
|
|
(1, ())
|
|
(2, (1, ()))
|
|
(3, (2, (1, ())))
|
|
...
|
|
|
|
Python has very nice "tuple packing and unpacking" in its syntax which
|
|
means we can directly "unpack" the expected arguments to a Joy function.
|
|
|
|
For example::
|
|
|
|
def dup((head, tail)):
|
|
return head, (head, tail)
|
|
|
|
We replace the argument "stack" by the expected structure of the stack,
|
|
in this case "(head, tail)", and Python takes care of unpacking the
|
|
incoming tuple and assigning values to the names. (Note that Python
|
|
syntax doesn't require parentheses around tuples used in expressions
|
|
where they would be redundant.)
|
|
'''
|
|
|
|
##We have two very simple functions to build up a stack from a Python
|
|
##iterable and also to iterate through a stack and yield its items
|
|
##one-by-one in order, and two functions to generate string representations
|
|
##of stacks::
|
|
##
|
|
## list_to_stack()
|
|
##
|
|
## iter_stack()
|
|
##
|
|
## expression_to_string() (prints left-to-right)
|
|
##
|
|
## stack_to_string() (prints right-to-left)
|
|
##
|
|
##
|
|
##A word about the stack data structure.
|
|
|
|
|
|
|
|
def list_to_stack(el, stack=()):
|
|
'''Convert a Python list (or other sequence) to a Joy stack::
|
|
|
|
[1, 2, 3] -> (1, (2, (3, ())))
|
|
|
|
'''
|
|
for item in reversed(el):
|
|
stack = item, stack
|
|
return stack
|
|
|
|
|
|
def iter_stack(stack):
|
|
'''Iterate through the items on the stack.'''
|
|
while stack:
|
|
item, stack = stack
|
|
yield item
|
|
|
|
|
|
def stack_to_string(stack):
|
|
'''
|
|
Return a "pretty print" string for a stack.
|
|
|
|
The items are written right-to-left::
|
|
|
|
(top, (second, ...)) -> '... second top'
|
|
'''
|
|
f = lambda stack: reversed(list(iter_stack(stack)))
|
|
return _to_string(stack, f)
|
|
|
|
|
|
def expression_to_string(expression):
|
|
'''
|
|
Return a "pretty print" string for a expression.
|
|
|
|
The items are written left-to-right::
|
|
|
|
(top, (second, ...)) -> 'top second ...'
|
|
'''
|
|
return _to_string(expression, iter_stack)
|
|
|
|
|
|
def _to_string(stack, f):
|
|
if isinstance(stack, long): return str(stack).rstrip('L')
|
|
if not isinstance(stack, tuple): return repr(stack)
|
|
if not stack: return '' # shortcut
|
|
return ' '.join(map(_s, f(stack)))
|
|
|
|
|
|
_s = lambda s: (
|
|
'[%s]' % expression_to_string(s) if isinstance(s, tuple)
|
|
else str(s).rstrip('L') if isinstance(s, long)
|
|
else repr(s)
|
|
)
|
|
|
|
|
|
def pushback(quote, expression):
|
|
'''Concatinate quote onto expression.
|
|
|
|
In joy [1 2] [3 4] would become [1 2 3 4].
|
|
'''
|
|
|
|
# Original implementation.
|
|
|
|
## return list_to_stack(list(iter_stack(quote)), expression)
|
|
|
|
# This is slightly faster and won't break the
|
|
# recursion limit on long quotes.
|
|
|
|
## temp = []
|
|
## while quote:
|
|
## item, quote = quote
|
|
## temp.append(item)
|
|
## for item in reversed(temp):
|
|
## expression = item, expression
|
|
## return expression
|
|
|
|
# This is the fastest, but will trigger
|
|
# RuntimeError: maximum recursion depth exceeded
|
|
# on quotes longer than sys.getrecursionlimit().
|
|
return (quote[0], pushback(quote[1], expression)) if quote else expression
|
|
|
|
|
|
def pick(s, n):
|
|
'''
|
|
Find the nth item on the stack. (Pick with zero is the same as "dup".)
|
|
'''
|
|
if n < 0:
|
|
raise ValueError
|
|
while True:
|
|
try:
|
|
item, s = s
|
|
except ValueError:
|
|
raise IndexError
|
|
n -= 1
|
|
if n < 0:
|
|
break
|
|
return item
|