Show HN: A lambda expression visualizer for the web

http://brycec.github.com/vizlamb/

by notb • 13 years ago

43 10 13 years ago

brycec.github.com

notb4• 13 years ago

The source is kinda crude at this point, but I hope to eventually allow named abstractions as well as direct manipulation of the tree (click n drag). Supporting types might be interesting as well.

DanWaterworth• 13 years ago

The text at the bottom says this is simply typed lambda calculus, but surely this is untyped lambda calculus.

notb4• 13 years ago

Right, thanks! Corrected.

Sniffnoy4• 13 years ago

The notation is cumbersome, but I like the visualization. I wish eta-reduction were implemented rather than just beta-reduction.

Unfortunately there appear to be some errors. Try entering the following expression:

#(##2 1)

This, if I've understood the notation correctly, means λx.(λy.λz.y)x. Thus, it should reduce to λx.λz.x, or ##2. However, the program instead reduces it to ##1, or λx.λz.z.

So, something's really wrong here.

notb4• 13 years ago

Agreed, it is unwieldy. However, because of it, eta-reduction is not as important because equivalent terms look the same, and name collisions can't happen. It made it a bit simpler.

And, that is definitely a bug, thanks. I think I could solve it by lazy evaluation (it wouldn't reduce that term) but I think I just need to correctly change vars when they move scope.

Sniffnoy4• 13 years ago

Not sure what you mean by "equivalent terms look the same". I'm not clear on how e.g. ##(2 1) and #1 look the same. Going by your remark about name collisions, I must ask if you are thinking of alpha-equivalence? (Which certainly is rendered unnecessary by the notational system.)

And thank you for making/hopefully fixing this!

tqs• 13 years ago

I think this would be really great with back and forward controls, i.e. rewind.

Show HN: A lambda expression visualizer for the web

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