Reduce duplication in interpreter.
Reduce duplication in interpreter.

diku-dk/futhark,mrakgr/futhark,mrakgr/futhark,ihc/futhark,HIPERFIT/futhark,diku-dk/futhark,ihc/futhark,HIPERFIT/futhark,diku-dk/futhark,diku-dk/futhark,diku-dk/futhark,ihc/futhark,HIPERFIT/futhark,mrakgr/futhark