do! keyword

Question

Quick question, what is the difference between do and do! in F#. I understand let and let! but can't find any resources on do!

Cheers.

Answer 1

Just as do is the unit-valued equivalent of let, do! is the unit-valued equivalent of let!

let! pat = expr in cexpr    //  desugars to b.Bind(expr,(fun pat -> «cexpr»))

do! expr in cexpr           // desugars to b.Bind(expr,(fun () -> «cexpr»)) 

Answer 2

You could also take a look at language specification (sec. 6.3.10 Computation Expressions):

http://research.microsoft.com/en-us/um/cambridge/projects/fsharp/manual/spec.html#_Toc321997063

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Petr

Answer 3

I found this old blog post very useful:

http://blogs.msdn.com/b/dsyme/archive/2007/09/22/some-details-on-f-computation-expressions-aka-monadic-or-workflow-syntax.aspx

Then, the "Interface" is described in: http://msdn.microsoft.com/en-us/library/dd233182.aspx