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…

## Programming with Bananas in Haskell (Versus OCaml)

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…

## Programming with Bananas in OCaml

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…

## Structural Versus Physical Comparsions in OCaml

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…

## Lexical Scoping in OCaml

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…

## Lambda Calculus in OCaml: “fun” and “function”

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: λx.λy.x+y (*A function expression*) λx.λy.x+y 3 4 (*A function application*) In OCaml,…

## Interfacing OCaml with PostgreSQL

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,…

## Using Dune to Build an OCaml Project

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)…

## Lazy or Eager? Order of Evaluation in Lambda Calculus and OCaml

Recall in lambda calculus, two items side by side is an application. One applies the left item (the function) to the right item (the input). E.g.: f x is read as “apply f to x“, in which f and x can be any lambda expressions. Therefore, f and/or x may be…

## Setting Up Merlin in Neovim

My OCaml development environment in Debian has been working well since I set it up. In this post I talk about setting up Merlin in vim and neovim. See this discussion for other well-liked OCaml environment set up. I’ve been using neovim and I like it so I’ll stick with…