67 lines
1.5 KiB
Markdown
67 lines
1.5 KiB
Markdown
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---
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title: "Pipelines"
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excerpt: "Documentation of the KCL language for the Zoo Design Studio."
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layout: manual
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---
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It can be hard to read repeated function calls, because of all the nested brackets.
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```norun
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i = 1
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x = h(g(f(i)))
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```
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You can make this easier to read by breaking it into many declarations, but that is a bit annoying.
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```norun
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i = 1
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x0 = f(i)
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x1 = g(x0)
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x = h(x1)
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```
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Instead, you can use the pipeline operator (`|>`) to simplify this.
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Basically, `x |> f(%)` is a shorthand for `f(x)`. The left-hand side of the `|>` gets put into
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the `%` in the right-hand side.
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So, this means `x |> f(%) |> g(%)` is shorthand for `g(f(x))`. The code example above, with its
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somewhat-clunky `x0` and `x1` constants could be rewritten as
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```norun
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i = 1
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x = i
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|> f(%)
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|> g(%)
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|> h(%)
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```
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This helps keep your code neat and avoid unnecessary declarations.
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## Pipelines and keyword arguments
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Say you have a long pipeline of sketch functions, like this:
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```norun
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startSketchOn(XZ)
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|> line(%, end = [3, 4])
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|> line(%, end = [10, 10])
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|> line(%, end = [-13, -14])
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|> close(%)
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```
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In this example, each function call outputs a sketch, and it gets put into the next function call via
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the `%`, into the first (unlabeled) argument.
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If a function call uses an unlabeled first parameter, it will default to `%` if it's not given. This
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means that `|> line(%, end = [3, 4])` and `|> line(end = [3, 4])` are equivalent! So the above
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could be rewritten as
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```norun
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startSketchOn(XZ)
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|> line(end = [3, 4])
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|> line(end = [10, 10])
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|> line(end = [-13, -14])
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|> close()
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```
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