Simple Goto problem

Question

In[1] Goto["place2"]; Label["place1"]; Return[10]; Label["place2"]; Return[20];

Out[1] Return[20]

In[2] f[x_] := (Goto[x]; Label["place1"]; Return[10]; Label["place2"]; Return[20];)

In[3] f["place2"]

Out[3] 20

Q1) Can you tell me why Out[1] is Return[20], not 20 ?

Q2) How to modify In[1] as slightly as possible, so that Out[1] becomes 20 ?

Thank you the comment is not related to my question but I learned something. — imida k, Aug 26 '21 at 21:16

score 6 · Accepted Answer · answered Aug 25 '21 at 23:39

6

First, why on earth do you want to use Goto??

But, if you must, the problem you're encountering is that Return typically returns from a control structure (e.g., If), and your example has none. When there is no control structure, the Return wrapper doesn't get stripped. To fix things, you can use the undocumented 2-arg form of Return (specifying CompoundExpression in this case, becase that is the FullForm of a; b; c):

Goto["place2"]; Label["place1"]; Return[10]; Label["place2"]; Return[20,CompoundExpression];

20

answered Aug 25 '21 at 23:39

Carl Woll

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Boy... Q: "I want to use a screwdriver to eat my soup." A: "Why on earth do you want to do that?? Well, if you must..." – David G. Stork Aug 25 '21 at 23:46
Thank you. I think it is hard to 'output something with exit' with goto. – imida k Aug 26 '21 at 20:55

score 0 · Answer 2 · answered Aug 26 '21 at 21:13

I think in mathematica,
when dealing with Goto command,
to make any final output on the screen,
following 4 things are necessary.

create a final variable
create a way-out
assign a value for the final variable
go to the way-out

In the below example, 1),2),3),4) are EndValue,"End",Endvalue=10 or 20,Goto["End"], respectively.

Goto["place1"]; Label["place1"]; EndValue = 10; Goto["End"];Label["place2"]; EndValue = 20; Goto["End"]; Label["End"]; EndValue

Also there is other method like using Return[something, CompoundExpression] as Carol answered.

Simple Goto problem

2 Answers2