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Two of my favorites are Haskell and Ruby. I like Haskell because it is computable category theory and Ruby because it is really easy to write scripts and other various prototype kinds of code. Although any language that has functional programming constructs and closures is usually fun to use. Maple and Mathematica fall in this category and they are fun to use when I need heavy duty symbolic and plotting facilities.

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Two of my favorites are Haskell and Ruby. I like Haskell because it is computable category theory and Ruby because it is really easy to write scripts and other various prototype kinds of code.