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#!/usr/bin/env python3
 
def unfoldTree(f, b):
    match f(b):
        case a, bs:
            return [a, [unfoldTree(f, b) for b in bs]]
 
def foldTree(f, tree):
    def go(node):
        match node:
            case x, ts:
                return f(x, [go(child) for child in ts])
    return go(tree)
 
if __name__ == '__main__':
 
    def buildNode(x):
        return (x, []) if 2 * x + 1 > 7 else (x, [2*x, 2*x + 1])
 
    # 二分木の生成
    print(unfoldTree(buildNode, 1))
    # 木の値の総和
    print(foldTree(lambda x, xs: sum([x] + xs), [1, [[2, []], [3, []]]]))
    # 木の値の最大値
    print(foldTree(lambda x, xs: max([x] + xs), [1, [[2, []], [3, []]]]))
    # 木の葉の個数
    print(foldTree(lambda x, xs: 1 if xs == [] else sum(xs), [1, [[2, []], [3, []]]]))
    # 木の高さ
    print(foldTree(lambda x, xs: 0 if xs == [] else 1 + max(xs), [1, [[2, []], [3, []]]]))
 
    # フィボナッチ数列
    def fib(n):
        def g(n):
            match n:
                case 0:
                    return (0, [])
                case 1:
                    return (1, [])
                case n:
                    return (n, [n - 1, n - 2])
        return foldTree(lambda x, xs: x if xs == [] else sum(xs), unfoldTree(g, n))
 
    print(fib(5))
 

Traceback (most recent call last):
  File "/usr/lib/python3.9/py_compile.py", line 144, in compile
    code = loader.source_to_code(source_bytes, dfile or file,
  File "<frozen importlib._bootstrap_external>", line 918, in source_to_code
  File "<frozen importlib._bootstrap>", line 228, in _call_with_frames_removed
  File "./prog.py", line 4
    match f(b):
          ^
SyntaxError: invalid syntax

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/lib/python3.9/py_compile.py", line 150, in compile
    raise py_exc
py_compile.PyCompileError:   File "./prog.py", line 4
    match f(b):
          ^
SyntaxError: invalid syntax

Standard output is empty