Anonymous functions and do in Julia

Arrows for throwaways; do blocks for multi-line arguments.

alts = [22.0, 47.5, 63.0, 81.5]

# Arrow syntax makes a throwaway function.
above_horizon = filter(a -> a > 30, alts)
println(above_horizon)

# do blocks hand a multi-line function to the first argument.
plans = map(alts) do alt
    band = alt > 60 ? "zenith" : "low"
    "slew to $alt ($band)"
end
foreach(println, plans)

How it works

a -> a > 30 is an anonymous predicate for filter.
map(alts) do alt ... end passes the block as the function.
foreach(println, plans) applies without collecting.

Keywords and builtins used here

do
end

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Step 3 of 3 in Functions, step 9 of 27 in Language basics.

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