mirror of https://git.sr.ht/~rabbits/modal
420 lines
15 KiB
Python
420 lines
15 KiB
Python
"""
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*------------------------------------------------------------*
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|modal.py : An Implementation of Modal in Python |
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|This is an implementation of Modal, a programming language |
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|based on term rewriting. This particular implementation |
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|is based on the idea of cyclic delimited string rewriting |
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|using a central queue and a dictionary of variable bindings.|
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|© 2019-2024 wryl, Paradigital |
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*------------------------------------------------------------*
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"""
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# `sys` for I/O and arguments.
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# `time` for measuring the runtime of the interpreter.
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import sys, time
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# A decorator intended for measuring the runtime of a given function.
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def measure(function):
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def measurement(*arguments):
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start = time.time()
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result = function(*arguments)
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end = time.time()
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milliseconds = (end - start) * 1000.0
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print("\nTook {:.3f}ms".format(milliseconds))
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return result
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return measurement
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# Enqueue an item by appending it to the queue.
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def enqueue(queue, item):
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return queue + item
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# Dequeue an item by slicing the queue. The last item is the head.
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def dequeue(queue, length=1):
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if length > len(queue):
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return queue
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return queue[length:]
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# Get the item(s) at the head of the queue.
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def peek(queue, length=1):
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if length > len(queue):
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return None
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if length == 1:
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return queue[0]
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return queue[:length]
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# Roll/cycle the queue by a certain amount by slicing.
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# This dequeues and enqueues a number of items, "cycling" the queue.
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def roll(queue, length=1):
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if length > len(queue):
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return queue
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return queue[length:] + queue[:length]
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# Seek to a certain position in the queue by repeatedly rolling it.
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def seek(queue, pattern):
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if pattern not in queue:
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return queue
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while peek(queue, len(pattern)) != pattern:
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queue = roll(queue)
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return queue
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# Extract a delimited fragment (subtree) from the queue.
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def extract(queue):
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results = []
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depth = 0
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for element in queue:
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if element[0] == "SRT":
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return []
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if element[0] == "INC":
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depth = depth + 1
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if element[0] == "DEC":
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if depth == 0:
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return results
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depth = depth - 1
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results.append(element)
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if depth == 0:
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return results
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return results
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# Generate a list of variable bindings from the current queue and a pattern.
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def match(pattern, queue, context=None):
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if context == None:
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context = {}
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if peek(queue) == None:
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return context
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for element in pattern:
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if element[0] == "VAR":
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variable = element[1]
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value = extract(queue)
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if variable in context:
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if context[variable] != value:
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return None
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queue = dequeue(queue, len(context[variable]))
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else:
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if len(value) == 0:
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return None
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context[variable] = value
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queue = dequeue(queue, len(context[variable]))
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elif element != peek(queue):
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return None
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else:
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queue = dequeue(queue)
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return context
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# Fill in a pattern with variables in it using a list of variable bindings.
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def construct(pattern, context):
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results = []
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for element in pattern:
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if element[0] == "VAR":
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if element[1] in context:
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for element in context[element[1]]:
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results.append(element)
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else:
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results.append(element)
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else:
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results.append(element)
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return results
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# Apply a pattern/replacement rule to the queue.
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def apply(queue, rules, pattern, replacement):
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context = match(pattern, queue)
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if context == None:
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return (False, roll(queue))
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pattern = construct(pattern, context)
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if not pattern:
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return (False, roll(queue))
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replacement = construct(replacement, context)
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return (True, enqueue(dequeue(queue, len(pattern)), replacement))
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def define(queue, rules, pattern):
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context = match(pattern, queue)
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left = context["left"]
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right = context["right"]
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if right and left:
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if len(left) > 1:
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left = left[1:][:-1]
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if len(right) > 1:
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right = right[1:][:-1]
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rules.append((left, apply, [right]))
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return (True, dequeue(queue, len(construct(pattern, context))))
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return (False, roll(queue))
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def undefine(queue, rules, pattern):
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context = match(pattern, queue)
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left = context["left"]
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if left:
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if len(left) > 1:
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left = left[1:][:-1]
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for rule, index in zip(rules, range(0, len(rules))):
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candidate , _, _ = rule
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if candidate == left:
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del rules[index]
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return (True, dequeue(queue, len(construct(pattern, context))))
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return (False, roll(queue))
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def add(queue, rules, pattern):
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context = match(pattern, queue)
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left = context["left"]
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right = context["right"]
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if left and right:
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if left[0][0] == "NUM" and right[0][0] == "NUM":
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queue = dequeue(queue, len(construct(pattern, context)))
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queue = enqueue(queue, parse(str(left[0][1] + right[0][1])))
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return (True, queue)
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return (False, roll(queue))
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def subtract(queue, rules, pattern):
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context = match(pattern, queue)
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left = context["left"]
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right = context["right"]
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if left and right:
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if left[0][0] == "NUM" and right[0][0] == "NUM":
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queue = dequeue(queue, len(construct(pattern, context)))
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queue = enqueue(queue, parse(str(left[0][1] - right[0][1])))
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return (True, queue)
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return (False, roll(queue))
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def multiply(queue, rules, pattern):
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context = match(pattern, queue)
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left = context["left"]
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right = context["right"]
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if left and right:
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if left[0][0] == "NUM" and right[0][0] == "NUM":
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queue = dequeue(queue, len(construct(pattern, context)))
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queue = enqueue(queue, parse(str(left[0][1] * right[0][1])))
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return (True, queue)
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return (False, roll(queue))
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def divide(queue, rules, pattern):
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context = match(pattern, queue)
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left = context["left"]
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right = context["right"]
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if left and right:
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if left[0][0] == "NUM" and right[0][0] == "NUM":
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queue = dequeue(queue, len(construct(pattern, context)))
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queue = enqueue(queue, parse(str(left[0][1] // right[0][1])))
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return (True, queue)
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return (False, roll(queue))
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def modulo(queue, rules, pattern):
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context = match(pattern, queue)
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left = context["left"]
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right = context["right"]
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if left and right:
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if left[0][0] == "NUM" and right[0][0] == "NUM":
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queue = dequeue(queue, len(construct(pattern, context)))
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queue = enqueue(queue, parse(str(left[0][1] % right[0][1])))
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return (True, queue)
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return (False, roll(queue))
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def display(queue, rules, pattern):
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context = match(pattern, queue)
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left = context["left"]
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if left:
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if left[0][0] == "LIT" or left[0][0] == "NUM":
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if left[0][1] == "space":
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print(' ', end="")
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elif left[0][1] == "newline":
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print('\n', end="")
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elif left[0][1] == "tab":
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print('\t', end="")
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else:
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print(left[0][1], end="")
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return (True, dequeue(queue, len(construct(pattern, context))))
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return (False, roll(queue))
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def applicable(rules, queue):
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results = []
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for pattern, operation, parameters in rules:
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if match(pattern, queue) != None:
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results.append((pattern, operation, parameters))
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return results
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def pick(list):
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if len(list) == 0:
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return None
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return list[0]
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def reconstruct(pattern):
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for element in pattern:
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if element[0] == "INC":
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yield '('
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elif element[0] == "DEC":
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yield ')'
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elif element[0] == "NUM":
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yield str(element[1])
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elif element[0] == "LIT":
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yield element[1]
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elif element[0] == "VAR":
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yield '?' + element[1]
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yield ' '
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def number(string):
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try:
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result = int(string)
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return True
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except:
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return False
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def literal(string, index=0):
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token = ""
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while index != len(string):
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character = string[index]
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if character in ['(', ')', '{', '}', '[', ']', '?', ' ', '\t', '\n', '\r']:
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break
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else:
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token = token + string[index]
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index = index + 1
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return (token, index)
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def parse(string, index=0):
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results = []
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while index != len(string):
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character = string[index]
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if character in ['(', ')', '{', '}', '[', ']', '?', ' ', '\t', '\n', '\r']:
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index = index + 1
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if character in ['(', '{', '[']:
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results.append(["INC"])
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elif character in [')', '}', ']']:
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results.append(["DEC"])
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elif character not in [' ', '\t', '\n', '\r']:
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token, index = literal(string, index)
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if character == '?':
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results.append(["VAR", token])
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elif number(token):
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results.append(["NUM", int(token)])
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else:
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results.append(["LIT", token])
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return results
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@measure
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def run(rules, queue, limit=pow(2, 32)):
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steps = 0
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failures = 0
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queue = [["SRT"]] + queue
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while failures != len(queue) and steps != limit:
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rule = pick(applicable(rules, queue))
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if rule == None:
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queue = roll(queue)
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failures = failures + 1
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else:
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pattern, operation, parameters = rule
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result, queue = operation(queue, rules, pattern, *parameters)
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if result == True:
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failures = 0
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#print("<>: ", inspect(seek(queue, ["SRT"])))
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#print("<>: ", inspect(queue))
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#input()
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steps = steps + 1
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if steps == limit:
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print("Execution limit reached.")
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return queue
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def read(file):
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try:
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with open(file) as file:
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content = file.read()
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return content
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except EnvironmentError:
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return None
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def inspect(pattern):
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return "".join(reconstruct(pattern))
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def usage(name):
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print(name + ':', "a programming language based on rewriting.")
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print("Usage:")
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print((' ' * 4) + name, "<file>")
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def prompt(prompt):
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try:
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return input(prompt)
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except:
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return None
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def help():
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prefix = ' ' * 4
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print("Commands:")
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print(prefix + "rules : Display the current ruleset.")
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print(prefix + "clear : Clear the current ruleset.")
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print(prefix + "help : This message.")
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print(prefix + "quit : Quit.")
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def main():
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defaults = [
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(parse("define ?left ?right"), define, []),
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(parse("undefine ?left"), undefine, []),
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(parse("add (?left) (?right)"), add, []),
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(parse("add (?left) ?right"), add, []),
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(parse("add ?left (?right)"), add, []),
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(parse("add ?left ?right"), add, []),
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(parse("subtract (?left) (?right)"), subtract, []),
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(parse("subtract (?left) ?right"), subtract, []),
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(parse("subtract ?left (?right)"), subtract, []),
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(parse("subtract ?left ?right"), subtract, []),
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(parse("multiply (?left) (?right)"), multiply, []),
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(parse("multiply (?left) ?right"), multiply, []),
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(parse("multiply ?left (?right)"), multiply, []),
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(parse("multiply ?left ?right"), multiply, []),
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(parse("divide (?left) (?right)"), divide, []),
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(parse("divide (?left) ?right"), divide, []),
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(parse("divide ?left (?right)"), divide, []),
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(parse("divide ?left ?right"), divide, []),
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(parse("modulo (?left) (?right)"), modulo, []),
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(parse("modulo (?left) ?right"), modulo, []),
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(parse("modulo ?left (?right)"), modulo, []),
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(parse("modulo ?left ?right"), modulo, []),
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(parse("(?left) + (?right)"), add, []),
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(parse("(?left) + ?right"), add, []),
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(parse("?left + (?right)"), add, []),
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(parse("?left + ?right"), add, []),
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(parse("(?left) - (?right)"), subtract, []),
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(parse("(?left) - ?right"), subtract, []),
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(parse("?left - (?right)"), subtract, []),
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(parse("?left - ?right"), subtract, []),
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(parse("(?left) * (?right)"), multiply, []),
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(parse("(?left) * ?right"), multiply, []),
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(parse("?left * (?right)"), multiply, []),
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(parse("?left * ?right"), multiply, []),
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(parse("?left / ?right"), divide, []),
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(parse("?left % ?right"), modulo, []),
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(parse("display ?left"), display, []),
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]
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rules = defaults.copy()
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if len(sys.argv) >= 2:
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content = read(sys.argv[1])
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if content == None:
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print("No such file.")
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return
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print("Initializating...")
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run(rules, parse(content))
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else:
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usage(sys.argv[0])
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return
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print("Modal v0.02")
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help()
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while True:
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input = prompt("::> ")
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if input == None:
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break
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elif parse(input) == parse("rules"):
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print("Rules:")
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prefix = ' ' * 4
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for pattern, operation, parameters in rules:
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if operation == apply:
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print(prefix + inspect(pattern) + "-> " + inspect(parameters[0]))
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elif parse(input) == parse("clear"):
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rules = defaults
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elif parse(input) == parse("help"):
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help()
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elif parse(input) == parse("quit") or parse(input) == parse("exit"):
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break
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else:
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print("Reducing...")
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print(inspect(seek(run(rules, parse(input)), ["SRT"])))
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return
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if __name__ == "__main__":
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main()
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