Exploring the breadth of software engineering.
While doing my OCaml MOOC exercise I came across a trie implementation for looking up words. I find that the way OCaml treats strings is very different from the way Haskell does it. It leads to different ways to implement the trie in the two languages. Strings and Tries in Haskell Haskell is a pure…
Run Time Versus Compile Time Error Run time errors are those that happen when the program runs, as opposed to compile time errors which happen when the program compiles. In a sense, having compile time errors is no big deal, because the errors guarantee that the ill-defined program won’t be running. The programmer can fix…
In the last post, I talked about catamorphisms in Haskell. Specifically, the advantages of the foldr1 or foldl1 option in Haskell. Namely, (1) not needing to specify the base case and (2) preserving polymorphisms in all applicable types. In this post, I will show another way to fold nonempty list without using foldr1 or foldl1…
In the last post I talked about catamorphisms in OCaml. In this post I compare that with Haskell. We’ll see that Haskell gives you more options when implementing catamorphisms. You don’t need to know Haskell to understand this post, I’ll introduce the required Haskell syntax along the way. Catamorphisms in Haskell As mentioned in the…
By bananas, I mean banana brackets as in the famous paper “Functional Programming with Bananas, Lenses, Envelopes and Barbed Wire” by Meijer et al. In this post I only focus on bananas, also called catamorphisms. Recursion is core to functional programming. Meijer et al. show that we can treat recursions as separate higher order functions…
The comparison operators in OCaml are polymorphic. That is, you can use them for various data types. Because OCaml is a typed language, like any other operator, you have to apply them to the same type. E.g., comparing a float to an int will give you a type error. OCaml can perform two types of…
Like many other modern languages, OCaml uses lexical (or static) scoping. That is, in OCaml, when your function includes a name that calls a variable, in the function, that variable has the value when the function is defined. The opposite is dynamic scoping, in which the variable has the value when the function is called. …
Lambda is fun! Lambda is certainly fun, but what I mean here is that the λ in lambda calculus is similar to the expression fun in OCaml. Recall that in lambda calculus, we have function expressions and function applications:
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λx.λy.x+y (*A function expression*) λx.λy.x+y 3 4 (*A function application*) |
In OCaml, you can express the same with –fun:
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fun x y -> x + y (fun x y -> x + y) 3 4 |
Each term separated by a space…
In the last post I talked about building an OCaml project using Dune. In this post I continue with a more complex project. The project interfaces OCaml and PostgreSQL (a database system) with Caqti (a third-party library that provides type-safe abstraction for interfacing with databases). I loosely follow this tutorial, but instead of using Jbuilder…
Dune is a popular OCaml build tool. If you haven’t already, I encourage you to give it a try! Especially if you are building a project that involves more components. See other compiling options here. You can install Dune using OPAM by running (in your system or a particular switch)
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opam install dune |
Writing a Dune File…