Fhree is a reference implementation of a small strongly typed functional language, it is interpreted and it implements the big-step operational semantics.

It is the result of some excercises for the Languages, Compilers and Interpreters course @ UniPi, and it's an extension of the FUN language shown by Prof. Galletta during the lectures.

The language is strongly inspired by OCaml, with some syntactical differences and simplifications.

The name Fhree is a word pun derived from the original language's name FUN.

Fun probably states for "Functional", but it can also mean "having fun", so the word pun would be "Fun for fun", whose acronym is FFF $\rightarrow$ F3 $\rightarrow$ F Three $\rightarrow$ F(h)ree.

Unlike in OCaml, there are no free variables. So there is no let construct but only let-in.

let x = 5 in x

For (also recursive) functions there is a construct fun similar to the OCaml's let-rec.

fun fact n = 
    if n = 0 then 1
    else n * fact (n - 1)
in fact 5

In order to have a strong type system, functions declaration make use of mandatory type annotations.

fun fact ( n : int ) : int = 
    if n = 0 then 1
    else n * fact (n - 1)
in fact 5

"lambda" |> lambda (s : string) : string -> " with annotation"

Type annotations are available in every construct, but optionally.

Fhree provides the most common data types: integers, floats, chars, booleans and strings.

Furthermore, it provides homogeneous lists of values and heterogeneous tuples.

There are both C/Java-like single-line comments and OCaml-like multi-line nested comments

// this is a comment

(* also
    (* this *) 
is a comment *)

Expressible and denotable values are

• integers

• booleans

• characters

• floats

• strings

• function closures

• tuples of values

• list of values

In addition to the type analysis, Fhree does a step of control-flow-analysis, using a fix-point algorithm. The result of the analysis of a file f is writed into a file f.cfa.

The CFA can be skipped passing the option --no-cfa, as you can read in the usage message.

There is also an option to do only the CFA, using Fhree as an analyzer.

Fhree is developed using OCaml and some OCaml tools for generating lexer and parser. For building the project, you must have these tools installed in your environment.

• OCaml and opam: follow the official instruction for you platform

• Menhir once you have installed opam, just run opam install menhir

To build Fhree just move in the directory and run make.

After that, you can run the interpreter of the language ./Fhree with the following options.

Usage: Fhree [--no-cfa | --cfa | --all] filename.F3
Options:
 --all
    default option: does a control-flow-analysis of the code and prints the result into filename.cfa then executes the program;
 --no-cfa 
    executes only the program, without analyzing the code;
 --cfa
    executes only the control-flow analyzer, without executing the program;

• Hexadecimal integers

• Free variables

• Unification algorithm for removing the mandatory type annotation in fun definitions

• Another unification algorithm for an implementation of pattern matching

• REPL

• Code generation for a simple compilation

• Uncurried functions definitions

  Multiple-argument function definition are now available! They make use of currying: they are parsed and converted in the corresponding curried - single-argument - functions: a function f

  fun f (a : t1) (b : t2) (c :t3) : tf = body;;

  is internally converted into

  fun f (a : t1) : (t2 -> t3 -> tf) -> 
      lambda (b : t2) : (t3 -> tf) -> 
          lambda (c : t3) : tf -> body