What is ___ vs _ in Mathematica ?

[Physics_rocks]

Hi guys ,

I have the next declaration in Mathematica :

myfunc [lis_list]

and myfync [x_,y___]

what does "lis_list" means ? I know that when I want to declare a variable of a function
I must write myfunc[SomeVar_] with one _
but what are 3 times _ (meaning ___)

I hope I'm no asking a stupid question :)

thanks !

 

[Hepth]

I don't think it does anything? Testing it, it seems to have no effect.

 

[Dale]

_ is a pattern which can stand for any single expression, whereas ___ is a pattern that can stand for any sequence of 0 or more expressions. There is also __ which is a pattern that can stand for any sequence of 1 or more expressions.

 

[Hurkyl]

what does "lis_list" means ?

It means that "lis" is only allowed to match a list, methinks. Mathematica's help system has a section on pattern matching -- it might be useful to go read it.