- Author
- Philip Wadler (paper); entry on Type Classes timeline
- Published
- June 1989
- Kind
- Short timeline entry about a 1989 paper, with no full text
- Original
- typeclasses.com/timeline/theorems-for-free
- Subject
- Checkable specs for coding agents
- Themes
- Checking the work
What it is
Type Classes, a training site for Haskell, hosts the entry. It marks the paper as the origin of what are now called free theorems. The page credits Philip Wadler as author.
What it says
- The paper introduced what are now called free theorems.
- Given only the type of a polymorphic function, a theorem it satisfies can be stated.
- The paper's stated purpose is to explain the trick behind this.
What evidence it gives
The page offers only a quoted passage from the paper and a date. It gives no proof, example or code. The trick itself is not described on the page.
Interests and limits
Only the short timeline entry was read, not Wadler's paper. The host site sells Haskell courses and projects. The page says nothing about how far free theorems reach.