if_else yields the exit block of the if

[Colton Williams]

when you do something like

with if_else as (then, otherwise):

    with then as then_block:

        <<code>>

    with otherwise as otherwise_block:

        <<code>>

the 'then_block' and 'otherwise_block' above are references to the same block, which is the endif block. I don't understand the motivation for that choice. If those blocks were actually the 'if' and 'else' blocks they could be more useful. For example you could do something like...

with builder.if_else as (then, otherwise):

    with then as then_block:

        var1 = builder.add(x,y)

    with otherwise as otherwise_block:

        var2 = builder.add(i, j)

phi = builder.phi()

phi.add_incoming(var1, then_block)

phi.add_incoming(var2, otherwise_block)

Does this seem like a good idea? The code change to do this is trivial (I'm using it in a forked repo). I'd be happy to create a PR if this would be useful to more people. All of the tests still pass in my forked version and I looked through the numba codebase and I couldn't find any instances where the yielded value of the then and otherwise was even being captured.

[Siu Kwan Lam]

The motivation comes from that the "endif" block is exposed only via code like "with then as endif", and that the "then_block" or "else_block" can always be accessed as "builder.basic_block".  When the code calls for a manual jump from within the if-else body to the "endif", the current behavior is more useful.  

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Siu Kwan Lam

Software Engineer

Continuum Analytics

[Colton Williams]

I don't see how you can directly access the then and else blocks. I know that the code you write within their context goes inside them, but they are not directly accessible from what I can tell. What if they yielded a tuple? Something like..............

with if_else as (then, otherwise):

    with then as (then, end):

        <<code>>

    with otherwise as (else_, end)

        <<code>>

[Siu Kwan Lam]

Here's a short notebook to demonstrate it.  Please see: https://gist.github.com/sklam/eb89eab5b5708f03d0b971136a9806f4

To view this discussion on the web visit https://groups.google.com/a/continuum.io/d/msgid/numba-users/62eb5281-dfc3-4a97-b032-f8a035ef2cff%40continuum.io.

For more options, visit https://groups.google.com/a/continuum.io/d/optout.

[Colton Williams]

I understand. That makes complete sense now. I really appreciate you taking the time to explain that to me.