This license was originally found in the "random" haskell package (http://hackage.haskell.org/package/random). It is Free and GPL-Compatible. There are now known to be many different variants of this license, with the only difference being that they appear in different revisions of the Haskell Reports, including (but not necessarily limited to) Haskell 98 Language Report, Haskell Report FFI Addendum, and Haskell 2010 Language Report. The clause that permits modification, as long as "it does not claim to be a definition of the Haskell 98 Language" can be seen as "prohibiting misrepresentation of the origin" of the modified version, a category of clauses traditionally treated as GPL-compatible.
All of these licenses are considered functionally identical, and share the same License tag: HaskellReport .
Haskell 98 Language Report
Code derived from the document "Report on the Programming Language Haskell 98", is distributed under the following license: Copyright (c) 2002 Simon Peyton Jones The authors intend this Report to belong to the entire Haskell community, and so we grant permission to copy and distribute it for any purpose, provided that it is reproduced in its entirety, including this Notice. Modified versions of this Report may also be copied and distributed for any purpose, provided that the modified version is clearly presented as such, and that it does not claim to be a definition of the Haskell 98 Language.