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If you have an Android phone/tablet and want to play around with the lambda calculus, I made an app that lets you build and evaluate expressions using a touch i

If you have an Android phone/tablet and want to play around with the lambda calculus, I made an app that lets you build and evaluate expressions using a touch interface: https://play.google.com/store/apps/details?id=com.alangpierce.lambdacalculusplayground https://play.google.com/store/apps/details?id=com.alangpierc... https://www.youtube.com/watch?v=0OzpqDDniDs https://www.youtube.com/watch?v=0OzpqDDniDs It's lower-level than the stuff in the post (you need to build booleans and math yourself) and doesn't have any instructional content built-in at the moment, but I think it's a nice way to see how far you can get using only lambda expressions. The most complicated thing I've done with it is used the Y combinator (among other things) to compute 6! = 720, which is a fun exercise.

futtetennista 10y ago
Very cool idea! Is it open source or are you thinking about it?
- alangpierce 10y ago
  Yep, it's on GitHub: https://github.com/alangpierce/lambdacalculusplayground https://github.com/alangpierce/lambdacalculusplayground I actually got mostly done porting it to React Native, but never totally finished it, so the GitHub repo is React Native and has some bugs. But you can go back in the git history to find the native Android SDK version that's currently on the Play Store.
  - diyseguy 10y ago
    Did I find the right point in the history? https://github.com/alangpierce/LambdaCalculusPlayground/tree/e3f939c8e8c18813407b354f8a4612ce5a050211 https://github.com/alangpierce/LambdaCalculusPlayground/tree...
    - alangpierce 10y ago
      Yep, that should work. Two commits earlier is the actual 1.1.0 release, before some restructuring to make room for the React Native stuff, so that may be a little better to work with. https://github.com/alangpierce/LambdaCalculusPlayground/commit/9073725d6825cb3dd50a28e4038d2743d3d941fa https://github.com/alangpierce/LambdaCalculusPlayground/comm...
urs2102 10y ago
Just out of curiosity, is there a particular reason why some people refer to lambda calculus with a definite article? My professor in CS Theory would refer to it as "the" lambda calculus, but another professor I had chose not to (I call it "lambda calculus"). This is totally trivial, I'm just wondering if there's a reason why you, or some people, say "the" lambda calculus.
- alangpierce 10y ago
  Good question. I think it's just an oddity/ambiguity of English (and other languages as well, I'm sure). I know that calculus (with derivatives and integrals) has been called "the calculus" in the past. I mostly just say "the lambda calculus" because that's what I've heard. Another way that it seems consistent in my mind is that there are many calculi (systems for computing things) out there, and the lambda calculus is one particular calculus that uses lambda expressions as the building block. The pi calculus is another example. The "the" feels a little more appropriate when "lambda" is seen as a modifier specifying which calculus I'm referring to. In other cases, I'll drop the "the", though. For example, I might say "There are three types of lambda calculus expressions.".
  - GeneralMayhem 10y ago
    Your final case isn't specific to "lambda calculus". In that sentence, you're using "lambda calculus" as a modifier for the general term "expressions", rather than referring to it on its own. Consider that you would say "There are three types of ceiling lights", but you would still say "the ceiling".
- wyager 10y ago
  "<x> calculus" without an article is an activity, whereas "the <x> calculus" is a concept. That's the way I've always parsed it internally. For example, you would never say to someone "Do you know about SKI Calculus?" because it's not something people do. You would say "Do you know about the SKI Calculus", referring to the abstract notion that someone constructed. We often use the phrase "calculus" for the calculus of derivatives and the calculus of integrals because it's something people do as an activity very often. Same with the lambda calculus.

futtetennista 10y ago

Very cool idea! Is it open source or are you thinking about it?

alangpierce 10y ago
Yep, it's on GitHub: https://github.com/alangpierce/lambdacalculusplayground https://github.com/alangpierce/lambdacalculusplayground I actually got mostly done porting it to React Native, but never totally finished it, so the GitHub repo is React Native and has some bugs. But you can go back in the git history to find the native Android SDK version that's currently on the Play Store.
- diyseguy 10y ago
  Did I find the right point in the history? https://github.com/alangpierce/LambdaCalculusPlayground/tree/e3f939c8e8c18813407b354f8a4612ce5a050211 https://github.com/alangpierce/LambdaCalculusPlayground/tree...
  - alangpierce 10y ago
    Yep, that should work. Two commits earlier is the actual 1.1.0 release, before some restructuring to make room for the React Native stuff, so that may be a little better to work with. https://github.com/alangpierce/LambdaCalculusPlayground/commit/9073725d6825cb3dd50a28e4038d2743d3d941fa https://github.com/alangpierce/LambdaCalculusPlayground/comm...

urs2102 10y ago

Just out of curiosity, is there a particular reason why some people refer to lambda calculus with a definite article? My professor in CS Theory would refer to it as "the" lambda calculus, but another professor I had chose not to (I call it "lambda calculus"). This is totally trivial, I'm just wondering if there's a reason why you, or some people, say "the" lambda calculus.

alangpierce 10y ago
Good question. I think it's just an oddity/ambiguity of English (and other languages as well, I'm sure). I know that calculus (with derivatives and integrals) has been called "the calculus" in the past. I mostly just say "the lambda calculus" because that's what I've heard. Another way that it seems consistent in my mind is that there are many calculi (systems for computing things) out there, and the lambda calculus is one particular calculus that uses lambda expressions as the building block. The pi calculus is another example. The "the" feels a little more appropriate when "lambda" is seen as a modifier specifying which calculus I'm referring to. In other cases, I'll drop the "the", though. For example, I might say "There are three types of lambda calculus expressions.".
- GeneralMayhem 10y ago
  Your final case isn't specific to "lambda calculus". In that sentence, you're using "lambda calculus" as a modifier for the general term "expressions", rather than referring to it on its own. Consider that you would say "There are three types of ceiling lights", but you would still say "the ceiling".
wyager 10y ago
"<x> calculus" without an article is an activity, whereas "the <x> calculus" is a concept. That's the way I've always parsed it internally. For example, you would never say to someone "Do you know about SKI Calculus?" because it's not something people do. You would say "Do you know about the SKI Calculus", referring to the abstract notion that someone constructed. We often use the phrase "calculus" for the calculus of derivatives and the calculus of integrals because it's something people do as an activity very often. Same with the lambda calculus.