70 lines
1.6 KiB
Python
70 lines
1.6 KiB
Python
import random
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# Write an evaluator for a small language:
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# - operators: '+', '*'
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# - operands: Integers
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#
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# E.g. evaluate("2+14*90+5*16")
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def tokenize(xs):
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result = []
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i = 0
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while i < len(xs):
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current = xs[i]
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if current in {'*', '+'}:
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result.append(current)
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i += 1
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continue
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elif current == ' ':
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i += 1
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continue
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else:
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i += 1
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while i < len(xs) and xs[i] in {str(x) for x in range(10)}:
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current += xs[i]
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i += 1
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result.append(int(current))
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return result
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def ast(tokens):
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result = []
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series = []
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for token in tokens:
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if token == '+':
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result.append(series)
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series = []
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elif token == '*':
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continue
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else:
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series.append(token)
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if series:
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result.append(series)
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return result
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def product(xs):
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result = 1
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for x in xs:
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result *= x
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return result
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def evaluate(x):
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tokens = tokenize(x)
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tree = ast(tokens)
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return sum([product(xs) for xs in tree])
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n = 7
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operands = [random.randint(0, 100) for _ in range(n)]
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operators = [random.choice(['+','*']) for _ in range(n - 1)]
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expr = []
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for i in range(n - 1):
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expr.append(operands[i])
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expr.append(operators[i])
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expr.append(operands[-1])
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expr = ' '.join([str(x) for x in expr])
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print("Expression: {}".format(expr))
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print("Tokens: {}".format(tokenize(expr)))
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print("AST: {}".format(ast(tokenize(expr))))
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print("Answer: {}".format(evaluate(expr)))
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assert evaluate(expr) == eval(expr)
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print("Success!")
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