Test if

#IF parser function

{{#show:Albania/OER| ?Has capital|link=none}} yields Tirana

{{#show:Hungary | ?In OECD}} yields "true"

{{#show:Brazil| ?In OECD}} yields ""

{{#if:string | yes | no}} yields "yes"

{{#if:{{#show:Brazil| ?In OECD}}| yes | no}} yields "no"

{{#if:{{#show:France| ?In OECD}}| yes | no}} yields "yes"

Thus:

{{#if:{{#show:Brazil| ?In OECD}}|Category:OECD|}} yields ""

{{#if:{{#show:France| ?In OECD}}|Category:OECD|}} yields "Category:OECD"

Thus:

[[{{#if:{{#show:France| ?In OECD}}|Category:OECD|}}]] yields ""

But the [[ ]] codes do not make it a valid category definition.

What about

{{#if:{{#show:France| ?In OECD}}|[[:Category:OECD]]|}} yields "Category:OECD"