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ANA BELL: So here's some code.

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I'm defining a
function named sq,

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and it takes in two parameters.

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I'm defining a function named
f, takes in one parameter,

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and then I'm doing
these two lines.

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The first one is just
calling function sq,

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and the next one is
just printing the value.

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So let's first see what-- nice.

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OK.

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Let's work through it.

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So The first things we see here
is two function definitions,

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right?

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So we don't currently
care about what's

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inside them right now because
we haven't made a function

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call yet.

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So the first thing we do
is we have the function

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call calc equal sq f and 2.

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OK?

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So inside sq, we're
going to have func and x.

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And func is going
to get mapped to f,

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and x is going to get
mapped to 2, right?

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So we're taking the
variables in order

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and mapping them to those.

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Func is f, and x is 2.

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First thing the
function does, sq,

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is create this variable
y is equal to x squared.

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So we're going to
have y is equal to 4.

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And then we're going
to return func y.

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So func of y, this is
going to be-- we're

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just replacing the
parameters f of 4, right?

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So now this is
another function call.

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We know what f is.

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This program knows what f is.

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f is going to be this part right
here, which returns x squared.

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OK?

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So in f, x gets mapped to
whatever variable we put in,

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which in this case is 4.

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And we're going to
return to whoever

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called us, which is over
here, 4 squared, which is 16.

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OK?

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So f of 4 gets replaced with 16.

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And f of 4 was up here, right?

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We're just popping
out of scopes now.

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So f of 4 was up here.

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So then that line there, return
func y, is going to return 16.

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And whoever called us was down
here, calc is equal to 16.

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And then we're
just printing calc.

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So 16 was right.

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Yay.