cond() - why ((t nill)) is common way to end the sublist?

[samifox]

hi

 

(cond
  ((= s "Y") 1) 
  ((= s "y") 1) 
  ((= s "N") 0) 
  ((= s "n") 0) 
  (t nil)
)

 

usually functions return nill when an empty value is issue, in cond returning nill is exposed to the developer...why?

[Tharwat]

With / without is the same return (nil).

[samifox]

So why its a common way?(according to docs)

[Tharwat]

I think it is just an example to beginners to know the use of t symbol with cond function and nothing's more.

[samifox]

Is there any use of t byond the self explained true?

[Tharwat]

Is there any use of t byond the self explained true?

As far as I know , no.

 

The use of t at the end of cond function is to pass any value you want if the arguments that passed to the function are not to equal to any value.

[samifox]

Not sure what u mean...

[Tharwat]

Not sure what u mean...

Do you know what is the use of symbol t at the end of cond function?

[samifox]

As i understand....if t equal to t...than return nill

[samifox]

Or maybe its a defult if none is true. But why?

[Tharwat]

No, if the variable s is not equal to either "Y" "y" "N" "n" the t symbol at the end would give you an option to set the variable ( for example ) to any value you want or print a message to user etc...

[samifox]

So its a defualt action in case none of the expression is true? So its could be (t (prints "illegel value"). So t is just a trigger in endcof the cond?

[Tharwat]

Close , have a look .

 

(cond
  ((= s "Y") 1) 
  ((= s "y") 1) 
  ((= s "N") 0) 
  ((= s "n") 0) 
  (t (alert "Variable (s) in not equal to any of the above check outs "))
)

[samifox]

Close , have a look .

 

(cond
  ((= s "Y") 1) 
  ((= s "y") 1) 
  ((= s "N") 0) 
  ((= s "n") 0) 
  (t (alert "Variable (s) in not equal to any of the above check outs "))
)

Its not what i meant?

[Lee Mac]

Put simply, a test expression of 't' will always be validated and so this represents a default condition for when all other conditions are not met; such a condition is by no means necessary, but usually provided by the documentation to help explain how to include a default condition.

 

It looks like you understand this.

[hugha]

The equivalent in another syntax style could be

 

 

if (s=="Y")

return 1

elseif (s=="y")

return 1

elseif (s=="N")

return 0

elseif (s=="n")

return 0

else

alert( "Variable (s) in not equal to any of the above check outs ")

endif

 

 

Think of (t ....) as being an all-inclusive "else" or "otherwise".