Hi there,
in structural operational semantics, an evaluation context is often used to
decompose an expression into a redex and its context. In a formal semantics on
paper, an expression can just be "pattern matched" over the grammar of an
evaluation context. If one wants to implement such a semantics in the form of an
interpreter, I could not come up with a similarly nice solution. I have declared
two separate data types (one for expressions, and one for evaluation contexts)
and explicit functions to convert an expression into a (evaluation context,
redex) pair.
For example, I could have
data Expr = Val Int | Plus Expr Expr
and
data Ctx = Hole | CPlusl Ctx Expr | CPlusr Int Expr
Are there any tricks to mimick more closely what is going on in the formal
semantics?
Klaus
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