Slicing, I/O and the Implicit State

Program slicing consists of deleting statements from a pro gram creating a reduced program a slice that preserves the original program s behaviour for a given set of variables at a chosen point in the program However some aspects of a program s semantics are not captured by a set of variables rendering slicing inapplica ble to their analysis These aspects of the program s state shall collectively be termed the implicit state For ex ample the input list supplied to a program is not denoted by a variable rather it is part of the implicit state It will be shown that this implicitness causes existing slicing algo rithms to produce incorrect slices with respect to input In order to solve the problem the program to be sliced will be transformed into an explicit version in which all aspects of its semantics are captured by variables The approach is also applied to a wider class of problems in which slicing is inhibited by the lack of variables upon which to form a suitable slicing criterion Because the approach can be expressed as a source level transformation it has the attractive property that the slic ing algorithm need not be altered