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Meaning of "do"
f#

I see a few usages of "do" but I'm still unsure what it means and when to use it.

Example 1,

type MyForm() as self =

class

inherit Form()

do self.Show()

end

Example 2,

do Application.Run(form)

In example 1 "do" is required, but doesn't seem to be in example 2 because the code still compiled without it. Can someone explain what "do" really means in above examples? What are the consequences of leaving "do" off what the code still runs?

If there are other "do" usage please let me know (except for "for x in xs do ...", I under that one :)

.

Pretty much any where you see it do means the next value you see is of type unit. As unit is F# equivalent of "void" to be useful, it will typically be some function call that has a side effect (which is the case in both your examples).

It is necessary when calling functions within a class definition (example 1) but optional at the top level (example 2).

By on 12/30/2008 11:27 PM ()

There is definitely some sickness around "do". For example:

1
2
3

> do do do do do do do printfn "Hello";;
Hello
val it : unit = ()

[6]

By on 12/31/2008 6:09 AM ()

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