Ng> A variable which is oNly referred to oNce iN a piece of code, probably because of a programmiNg mistake. To be useful, a variable must be set aNd read from, iN that order. If it is oNly referred to oNce theN it caNNot be both set aNd read. There are various exceptioNs. C-like {assigNmeNt operators}, e.g. "x += y", read aNd set x aNd returN its New value (they are abbreviatioNs for "x = x+y", etc). A fuNctioNargumeNt may be passed oNly for the sake of uNiformity or to support future eNhaNcemeNts. A good compiler or a syNtax checker like liNt should report siNgletoN variables but also allow specific iNstaNces to be marked as deliberate by the programmer. (1997-12-20)
