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authorKartik K. Agaram <vc@akkartik.com>2015-11-08 21:29:56 -0800
committerKartik K. Agaram <vc@akkartik.com>2015-11-08 21:29:56 -0800
commitb766f5f8747166b688413d15375880be510d8af6 (patch)
tree7d97f184e3f50fe5147e1ba71fc433dc215e4a59 /factorial.mu
parent92e3f56ef967185f19522e698872ff61ef4ef284 (diff)
downloadmu-b766f5f8747166b688413d15375880be510d8af6.tar.gz
2404 - ah, finally a useful assertion
And it caught a bug: I mean to always update type names and types in
sync.

The last month or so I've been getting reluctantly but inexorably
converted to the need and value of a type system. First I thought I just
need a minimal but rigorous type system to avoid memory corruption and
security issues. Now I think I also want it to be expressive enough to
be able to express what data different phases in a compiler read and
write, and to be able to designate specific fields as 'fully computed'
so that we can statically check that phases wait until their data is
available.

The phase-ordering problem in a compiler is perhaps the canary in the
coal-mine for a more general problem: even small changes can
dramatically explode the state space if they violate assumptions
previously held about the domain. My understanding of when type pointers
are null and not null is immeasurably more nuanced today than it was a
week ago, but I didn't need the nuance until I introduced generic
functions. That initial draft of a hundred lines bumped me up to a much
larger state space. How to make it more obvious when something happens
that is akin to discovering a new continent, or finding oneself
teleported to Jupiter?

Assumptions can be implicit or explicit. Perhaps a delete of an
assertion should be estimated at 1000 LoC of complexity?
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