The main purpose of GNU poke is to manipulate structured binary data in terms of abstractions provided by the user. The Poke type definitions can be seen as a sort of declarative specifications for decoding and encoding procedures. The user specifies the structure of the data to be manipulated, and poke uses that information to automagically decode and encode the data. Under this perspective, struct types correspond to sequences of instructions, array types to repetitions or loops, union types to alternatives or conditionals, and so on.