Defining and Calling Functions

fn, a name, parameters in square brackets, an indented body:

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fn area[w, h]
    return w * h

log[area[3, 4]]

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The last expression in a body is the return value, so return on the final line is optional:

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fn cube[x]
    x * x * x

log[cube[3]]

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Functions Are Values

A function name without brackets is the function — store it, pass it, call it later. This is how Crow does everything other languages use lambdas for (Crow has no lambdas — a deliberate choice; named functions keep every callsite greppable and every behavior testable):

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fn cube[x]
    x * x * x

op = cube
log[op[2]]

fn apply_twice[f, x]
    return f[f[x]]

log[apply_twice[cube, 2]]

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512