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This page will describe the design, usage and motivation for CTRex.

CTRex is a library for Haskell which implements extensible records using closed type families and type literals. It does not use overlapping instances.

What are extensible records?

A record is just a collection of label-value pairs. For example: { x = 0 , y = "bla", z = False }

Labels (such as x,y and z) in CTRex are type level symbols (i.e. type level strings). We can point to a label by using the label type:

data Label (s :: Symbol) = Label

For example, we can declare shorthands for pointing at the type level symbol "x", "y" and "z" as follows.

x = Label :: Label "x" y = Label :: Label "y" z = Label :: Label "z"