# Local variables whose definitions depend on each other [duplicate]

This question already has an answer here:

Consider the following (pseudo-)function definition:

f[l_] := Let[{
a = Length[l],
b = First[l],
c = b/a,
}, c*10]


So for instance, f[{2,3,4,5}] should output 5.

Currently, I only know variants for Let that

• set a, b and c globally (on the first call of f) or
• don't allow the definition of c because a and b are not defined.

What is the most simple way to define local variables whose definitions may depend on each other (upwards)?

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## marked as duplicate by R. M.♦Aug 27 '14 at 18:21

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

## 2 Answers

If you have Version 10 use the function Where in the GeneralUtilities package like this:

Needs["GeneralUtilities"]

f[l_] := Where[a = Length[l], b = First[l], c = b/a, c*10]


Then:

f[{2, 3, 4, 5}]


5

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I think it would be better to post this answer to the related main post so that it can be easily found (see link in question) – R. M. Aug 27 '14 at 18:23

Why not just this?

f[l_] := Block[{a,b,c},
a = Length[l];
b = First[l];
c = b/a;
c*10]


Then

f[{2, 3, 4, 5}]

5

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Ah, so that's how you use Block`. Thanks! – Raphael Aug 28 '14 at 9:43