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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 The Toad 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 2

up vote 6 down vote accepted

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


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


f[{2, 3, 4, 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) –  The Toad 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;


f[{2, 3, 4, 5}]
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Ah, so that's how you use Block. Thanks! –  Raphael Aug 28 '14 at 9:43

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