Errata

printfn "Hello, World",
shouldn't have a comma at the end

Note from the Author or Editor:
Thank you for pointing that out, it will be fixed in subsequent printings.

let getCustomerByID id =
query {
for customer in db.Customers do
where customer.CustomerID = id
select c
head
}

should be

let getCustomerByID id =
query {
for customer in db.Customers do
where (customer.CustomerID = id) // fix error: Arguments to query operators may require parentheses, e.g. 'where (x > y)' or 'groupBy (x.Length / 10)'
select customer // fix error: The value or constructor 'c' is not defined
head
}

Note from the Author or Editor:
Thank you for pointing this out, it will be fixed in a subsequent printing.

let probabilityOfPercipitation =
parsedXmlDoc
.data.[0]
.parameters.[0]
.probabilityofprecipitation.[0]
.value.[0].Value;;

These 3rd and below lines should be indented.
Otherwise, I got the following error:
error FS0010: Unexpected symbol '.' in binding.

In addition, I failed to get probabilityOfPercipitation (I think this name is a typo: probabilityOfPrecipitation is correct) when I created SampleXmlDocWrapperLibrary.dll from a sample listed in P378-379.
This might be because '/dwml/data/parameters/probability-of-precipitation' element contains only one 'value' element in the sample so the type of probabilityofprecipitation's value property is not an array but string.
To fix the error, I simply added another 'value' element under 'probability-of-precipitation' and re-created the wrapper dll.

Note from the Author or Editor:
Thank you for pointing this out, I'll make sure it gets fixed in a subsequent printing of the book.