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(make-If true X Y) => X (make-If false X Y) => Y (make-If X true false) => X (make-If X Y Y) => Y (make-If X Y Z) => (make-If X Y\[X <\- true\] Z\[X <\- false\]) |
The notation M[X <- N] means M with all occurrences of the symbol X replaced by the expression N. It is very costly to actually perform these substitutions on NormIfExp data. To avoid this computational expense, we simply maintain a list of bindings which are pairs consisting of symbols (variable names) and boolean values {true, false. The following data definition definition formally defines the binding type.
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