I must have thought that there was nothing more
Absurd than that love is just a four letter word

— Bob Dylan

Love is just a four letter word. No doubt about it. At least in the English language this is perfectly true, which is easy to (jokingly) prove in a short Haskell REPL session:

λ> length "love" == 4
True

On the other hand, it feels totally wrong. Bob Dylan’s song is a good example: The Lady uttering this phrase seems using it as a kind of magic spell trying to avoid getting hurt by deeper emotions. But in doing so, she in turn hurts the people who are in love with her.

So stating “love is a four letter word” is true, but reduces the actual phenomenon to a meaningless sequence of characters and does not help to explain anything. (This may also be the reason why there are so many songs proclaiming “love is not a four letter word”.)

Lambda is not a four letter word is true in the same sense:

λ> length "lambda" /= 4
True

And in quite the same way as the sentence on love it does not help. It’s not wrong in the orthographical sense, but it does not help to get any deeper insights into λ-calculus or functional programming.

So, since it is obviously quite difficult to fully grasp a complex phenomenon in short definitions - be it love or λ, there is probably no way around approaching the subject in somewhat longer texts in ever new paraphrases. Hence this blog!

As my late professor said:

Whereof one cannot speak, thereof one must write!

— Rudolf Kaehr

Thomas Mahler