#2742 expr {"Nan"}

[Anonymous]

The expr command, when given the literal string "Nan"
(quotes included), tries to convert Nan to a number and
yields the error:

domain error: argument not in valid range

Clearly, what's inside quotes is not expr's business,
it shouldn't open that box !

Also notice that this strange behavior is insensitive
to whitespace, but it to other characters:

expr {"Nan xyz"}

works correctly.

[Alexandre Ferrieux]

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This was me (sorry I hadn't logged in).
Maybe one useful detail:

The same problem arises if the Nan results from an evaluation:

proc foobar {} {return Nan}
expr {[foobar]}

So we can reinterpret this as: "expr systematically tries to
convert its final result to a number". This is at odds with
Tcl's lazy conversion spirit, and definitely a bug !

-Alex

[Don Porter]

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be sure to reconcile any
changes here with Bug 218000

[Donal K. Fellows]

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Tcl's NaN handling is an utter mess. But [expr] is (IIRC)
defined to be aggressive about trying to convert its result
into numeric form.

[Nobody/Anonymous]

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sorry, i couldn't logged in

i tried this command but not foumd any error in it as it
printing "Nan"

[Alexandre Ferrieux]

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Look at the header: I tried this on 8.3.5.
So please give the [info patchlevel] where you no longer
have the bug.
I'd like to know the critical version where this was fixed.
Any idea, frome those who know expr's changelog by heart ?

-Alex

[Donal K. Fellows]

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8.4 had a bit of work in this area, but it turns out that
many platform libc's aren't good here. :^(

[Donal K. Fellows]

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The expr.n manual page states that:
"If an operand does not have one of the integer formats
given above, then it is treated as a floating-point number
if that is possible."

Thus, [expr] is correct to regard "Nan" as a float, and is
at least not vastly wrong in regarding that as a domain
error (because that's what generates NaN values normally.)
8.4 should be a bit better at handling this.