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decomposing values in let no longer works in CTP build?
f#compiler

Please consider a type like

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type Extent = TextSpan of int*int

where the integer denote the start and the end of a block of text. I have tons of code that contains decompositions like

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let StartOf e = let TextSpan(s,_) = e in s

This now gives a compiler diagnostic about s not being defined. I'm speculating that the compiler does not enter the s in the TextSpan constructor in the current scope so that it is not visible in the in part.

I know that I can rewrite the code to use match instead, but it does seem like too blatant to be a bug. After all, this code used to work perfectly.

Any ideas?

.

Hi,
the syntax above is ambiguous, because the compiler doesn't know whether you're declaring a function (named TextSpan with a tuple as an argument) or whether you're decomposing a value. This is probably the reason why this syntax was deprecated. You can correct it easily by adding additional parentheses:

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let StartOf e = let (TextSpan(s,_)) = e in s

// .. and you can even write:
let StartOf(TextSpan(s,_)) = s
By on 12/18/2008 2:37 AM ()

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