I'm working through Pierce's Types and Programming Languages on my own. I'm attempting to write the typecheckers in Haskell, instead of ML. However, when it comes to his eval function, I'm a little stuck. The original is
let rec eval t = try let t' = eval1 t in eval t' with NoRuleApplies - tWhere
Steve Downey wrote:
It makes eval1 a bit more complicated, and not as straightforward
translation from the type system being described, though.
e.g reducing If looks more like
eval1 (TmIfExpr t1 t2 t3) =
let t1' = eval1 t1
in case t1' of
{ Just t1'' - Just $ TmIfExpr t1''
Steve Downey wrote:
] I'm considering changing eval1 to be ArithExpr-Maybe ArithExpr
]
] If the expression is reducible, then I return Just t, and if it's not
] reducible, then Nothing
]
] It makes eval1 a bit more complicated, and not as straightforward
] translation from the type system being
