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33 lines
2 KiB
Markdown
33 lines
2 KiB
Markdown
# A note on the complexity of Miller's expression language
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One of Miller's strengths is its brevity: it's much quicker -- and less
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error-prone -- to type `mlr stats1 -a sum -f x,y -g a,b` than having to track
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summation variables as in `awk`, or using Miller's [out-of-stream
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variables](reference-dsl-variables.md#out-of-stream-variables). And the more
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language features Miller's put-DSL has (for-loops, if-statements, nested
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control structures, user-defined functions, etc.) then the *less* powerful it
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begins to seem: because of the other programming-language features it *doesn't*
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have (classes, exceptions, and so on).
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When I was originally prototyping Miller in 2015, the primary decision I had
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was whether to hand-code in a low-level language like C or Rust or Go, with my
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own hand-rolled DSL, or whether to use a higher-level language (like Python or
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Lua or Nim) and let the `put` statements be handled by the implementation
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language's own `eval`: the implementation language would take the place of a
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DSL. Multiple performance experiments showed me I could get better throughput
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using the former, by a wide margin. So Miller is Go under the hood with a
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hand-rolled DSL.
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I do want to keep focusing on what Miller is good at -- concise notation, low
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latency, and high throughput -- and not add too much in terms of
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high-level-language features to the DSL. That said, some sort of
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customizability is a basic thing to want. As of 4.1.0 we have recursive
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`for`/`while`/`if` [structures](reference-dsl-control-structures.md) on about
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the same complexity level as `awk`; as of 5.0.0 we have [user-defined
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functions](reference-dsl-user-defined-functions.md) and [map-valued
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variables](reference-dsl-variables.md), again on about the same complexity level
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as `awk` along with optional type-declaration syntax; as of Miller 6 we have
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full support for [arrays](reference-dsl-arrays.md). While I'm excited by these
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powerful language features, I hope to keep new features focused on Miller's
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sweet spot which is speed plus simplicity.
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