Given: data X = (:*){ x :: Int, y :: Int } deriving(Show) which is syntactically correct:
constr -> con { fielddecl[1] , ... , fielddecl[n] } (n>=0) con -> ( consym )
and the following from 10.4: * If the constructor is defined to be an infix operator, then the derived Read instance will parse only infix applications of the constructor (not the prefix form). * If the constructor is defined using record syntax, the derived Read will parse only the record-syntax form, and furthermore, the fields must be given in the same order as the original declaration. the behavor of the Show instance seems to be contradicted, since :+ is an infix operator and is defined using record syntax. Suggested resolution: * If the constructor is defined using infix syntax, then the derived Read instance will parse only infix applications of the constructor (not the prefix form). Thus, 'data X = Int :+ Int' would show infix but 'data X = (:+) Int Int' would not. Alternatively, change the con in the above production for constr to conid, thus banning infix record constructors. Status: stefan@stefans:/tmp$ cat Main.hs data X = (:*) { x :: Int, y :: Int } deriving(Show) main = print ((:*) 2 2) stefan@stefans:/tmp$ runghc Main.hs (:*) {x = 2, y = 2} stefan@stefans:/tmp$ runhugs Main.hs :* {x = 2, y = 2} stefan@stefans:/tmp$ yhc Main.hs Compiling Main ( Main.hs ) stefan@stefans:/tmp$ yhi Main.hbc 2 :* 2 stefan@stefans:/tmp$ Note that the hugs output for this corner case is unparseable and thus buggy! Stefan