I have tried out functional programming various times over the years. Over one span of some months I used OCaml to create something interesting. Maybe an OWL parser. That convinced me that something like ML was far superior for parsers.
And I have experimented a few other times, such as with LiveScript.
The last time I tried to stick with a functional design was maybe a year or two ago. I ended up repeatedly passing around a lot of parameters so that many functions had several parameters. For example, in order to make a decision, I had to analyze something in several ways, collect that analysis, and make a decision based on all of the variables in the end. So the parameters just started building up until the last function had like a dozen of them.
Then I grouped some of them into structures, but the functions that operated on those structures had a few names parameters which were named in the decision function. So even though I had fewer inputs to the decision, the function body was complex with numerous parameters.
This led me to use classes to encapsulate the state so that parameters did not always need to be passed at the end since they could refer to internal state.
And I have experimented a few other times, such as with LiveScript.
The last time I tried to stick with a functional design was maybe a year or two ago. I ended up repeatedly passing around a lot of parameters so that many functions had several parameters. For example, in order to make a decision, I had to analyze something in several ways, collect that analysis, and make a decision based on all of the variables in the end. So the parameters just started building up until the last function had like a dozen of them.
Then I grouped some of them into structures, but the functions that operated on those structures had a few names parameters which were named in the decision function. So even though I had fewer inputs to the decision, the function body was complex with numerous parameters.
This led me to use classes to encapsulate the state so that parameters did not always need to be passed at the end since they could refer to internal state.