casting string as integer or double

I've been trying to cast a string from an attribute value as a integer. The
value of the attribute will always be a positive whole number. I'm using it as a
parameter in a called template that will use it as an decrementer. The document
is well formed  but not validated against any schema/dtd

I've tried the following outside of the called template

<xsl:variable name="l_Decrementer" select="@cols cast as xs:integer" />

<xsl:variable name="l_Decrementer" select="@cols" as="xs:integer" />

and

<xsl:with-param name="p_Decrementer" select="@cols cast as xs:integer" />

Any help will be appreciated.

Thanks in advance

MM