Use of semi-colons in If[]

Question

This is the code in Mathematica:

h[x_] := (If[x > 5, Return[big]]; t = x^3; Return[t - 7])

I fully understand what the code does, with h[4]=4^3-7=57 and h[6]=h[7]=big but I have the following issues:

h[x_] does not function if I remove the brackets () ie h[x_]If[x > 5, Return[big]]; t = x^3; Return[t - 7] , what is the function of () in the code?
Can someone also explain the significance of the semi-colons in this code, and what is it used instead of commas (which make the code not work). What are the benefits of using ; instead of , in code?

The code isn't that great; among other things, you have a global t in there which can be problematic if you're using t somewhere else. Try h[x_] := Block[{t}, If[x > 5, big, t = x^3; t - 7]] (but even that is not the best way to do it). Also, look up CompoundExpression[]. — J. M.'s technical difficulties♦, Oct 14 '18 at 18:18
function definition has a high priority. Without the () the function definition would end at the first semicolon. With the () the function definition is the whole line. The If[] tests x and potentially bails out with the value big. If it doesn't bail out then the t=x^3;Return[t-7] is all done. Be cautious with Return because people have reported problems with that. — Bill, Oct 14 '18 at 18:21

bill s · Accepted Answer · 2018-10-14 21:24:15Z

1

I might try to write the function a bit more simply as:

h[x_] := If[x > 5, big, x^3 - 7]

Then you can see it working by evaluating on the first 8 integers:

h /@ Range[8]
{-6, 1, 20, 57, 118, big, big, big}

answered Oct 14 '18 at 21:24

bill s

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$\begingroup$ Nit-picky: To get exactly the same functionality, you'd want something like If[TrueQ[x > 5], big, x^3 - 7], so that h[z] would return z^3 - 7 instead of an If[] statement. But I expect the OP hasn't thought through that case yet and is assuming x is a real number. $\endgroup$ – Michael E2 Oct 14 '18 at 21:41

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