Abstract:
Plotkin, in his seminal article Call-by-name,
call-by-value and the  -calculus, formalized evaluation strategies
and simulations using operational semantics and continuations. In particular,
he showed how call-by-name evaluation could be simulated under call-by-value
evaluation and vice versa. Since Algol 60, however, call-by-name is both
implemented and simulated with thunks rather than with continuations. We
recast this folk theorem in Plotkin's setting, and show that thunks, even
though they are simpler than continuations, are sufficient for establishing
all the correctness properties of Plotkin's call-by-name simulation.
Furthermore, we establish a new relationship between Plotkin's two
continuation-based simulations  and  , by
deriving as the composition of our thunk-based simulation
 and of  -- an extension of handling
thunks. Almost all of the correctness properties of follow from
the properties of and . This simplifies reasoning
about call-by-name continuation-passing style. We also give several
applications involving factoring continuation-based transformations using
thunks
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