Modular•10mo ago

Compilation does not terminate for recursive function

I'm porting some C++ with templates, and I realize that there is no such thing as if constexpr in mojo. Im trying to write something similar to the following test. However, compilation (not surprisingly) does not terminate. Question: how do other people handle these straightforward recursive functions?

fn test[N: Int]() -> InlinedFixedVector[Int, 1<<N]:
    if N == 0: 
        var result = InlinedFixedVector[Int, 1<<N](1<<N)
        result[0] = 0
        return result
    else:
        alias N2: Int = N-1
        let sub: InlinedFixedVector[Int, 1<<N2] = test[N2]()
        let subsize = 1<<N2

        var result = InlinedFixedVector[Int, 1<<N](1<<N)
        for i in range(subsize):
            result[i] = sub[i]
            result[i + subsize] = sub[i] + subsize
        return result

fn test[N: Int]() -> InlinedFixedVector[Int, 1<<N]:
    if N == 0: 
        var result = InlinedFixedVector[Int, 1<<N](1<<N)
        result[0] = 0
        return result
    else:
        alias N2: Int = N-1
        let sub: InlinedFixedVector[Int, 1<<N2] = test[N2]()
        let subsize = 1<<N2

        var result = InlinedFixedVector[Int, 1<<N](1<<N)
        for i in range(subsize):
            result[i] = sub[i]
            result[i + subsize] = sub[i] + subsize
        return result

2 Replies

Alex Kirchhoff•10mo ago

I believe @parameter if in Mojo is quite similar to if constexpr in C++ -- does that work?

Henk-Jan Lebbink•10mo ago

@Alex Kirchhoff Thank you, Yes that solves my issues. I missed that somewhat important line in the doc.

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Compilation does not terminate for recursive function