Martijn van Steenbergen wrote:
Tom Schrijvers wrote:
data EvalDict sem = EvalDict { val :: Int -> sem Int, add :: sem Int
-> sem Int -> sem Int }
An alternative option is to capture the structure in a GADT:
data Eval a where
Val :: Int -> Eval Int
Add :: Eval Int -> Eval Int -> Eval Int
And then write what were instances before as functions Eval a -> whatever.
But these interpreter functions Eval a -> whatever would have to use
pattern matching at runtime to discover the structure of the term, so
this approach is no longer tagless.
Tillmann
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