作者：RobertHarperCarnegieMellonUniversityThisisaworkingdraftofabookonthefoundationsofprogramminglanguages.Thecentralorganizingprincipleofthebookisthatprogramminglanguagefeaturesmaybeseenasmanifestationsofanunderlyingtypestructurethatgovernsitssyntaxandsemantics.Theemphasis,therefore,i