Klaus Didrich Andreas Fett Carola Gerke Wolfgang Grieskamp Peter Pepper OPAL: Design and Implementation of an Algebraic Programming Language. 228-244 1994 conf/plsa/1994 Programming Languages and System Architectures db/conf/plsa/plsa1994.html#DidrichFGGP94 http://dx.doi.org/10.1007/3-540-57840-4_34