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A comment on Why Haskell is beyond ready for Prime Time. Parent comment
The paper "Theorems for free" describes this: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.38.9...
Here's an example... let's say a function has type
[a] -> [a]
Just by looking at that type, the function has a number of properties.
1. The set of items in the result list are a subset (non-proper) of the set of items in the input list
2. Membership in the result list cannot be determined by the values of the members in the input list... ONLY by position
So, some functions that fit this type and therefore fit these properties...
1. id
2. reverse
3. tail
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The paper "Theorems for free" describes this: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.38.9...
Here's an example... let's say a function has type
[a] -> [a]
Just by looking at that type, the function has a number of properties.
1. The set of items in the result list are a subset (non-proper) of the set of items in the input list
2. Membership in the result list cannot be determined by the values of the members in the input list... ONLY by position
So, some functions that fit this type and therefore fit these properties...
1. id
2. reverse
3. tail