Note: This repo is no longer updated. Trustee
is an extension of Fhree, revised and improved.
Fhree is a reference implementation of a small strongly and statically 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
Unlike in OCaml, there are no free variables. So there is no let construct but only let-in.
let x = 5 in x
There is a shorthand for this, by means of ;
:
let x = 5;
For (also recursive) functions there is a construct let-fun similar to the OCaml's let-rec.
let 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.
let fun fact ( n : int ) : int =
if n = 0 then 1
else n * fact (n - 1)
in fact 5
Functions can be used also without declaration, this allows to have both lambdas and recursive lambdas:
5 |> (
fun fact ( n : int ) : int =
if n = 0 then 1
else n * fact (n - 1)
)
"anon-fun" |> lambda (s : string) : string -> " with annotation"
Type annotations are available also in every other 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.
Type | Literal examples | Operators | Meaning |
---|---|---|---|
int | -5 , 0 , 42 |
+ - * / % |
Arithmetic operations on ints |
float | 0.15 , .0002 ,0.1e-22 , |
+. -. *. /. |
Arithmetic operations on floats |
string | "Hello World" |
^ |
Concatenation of strings |
boolean | true , false |
&& || |
|
tuple | ('a', 0, "hi!") ,(0,1) |
proj t i |
Projection of the i-th element of t |
list | [2, 4, 6, 8] , [] , ["Hello!"] |
hd l tl e::l is_empty l |
Get the first element of l Get l without the first element Add e in head of l Tests if l is empty |
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
There are IO directives for each data type. The format for the type T
is get_T
/print_T
.
IO functions are still expressions, and thus evaluation returns a value. In particular, print
functions are evaluated to the special value Unit
.
let fun fact(n : int) : int =
let _ = print_int n in // sequencing
if n = 0 then
1
else
n * fact (n - 1)
in get_int () |> fact
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 is skipped by default (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
Options:
--no-cfa
default option: executes only the program, without analyzing the control-flow;
--cfa
executes only the control-flow analyzer, without executing the program;
--all
does a control-flow-analysis of the code and prints the result into filename.cfa
then executes the program;
- An empty program is still a correct program (with
Unit
value). - There is a single sequencing expression, that is
let ... in
. - The language requires type annotation for function parameter and return type.
- The construct
Proj t i
takes a tuple and an integer literal! That's motivated by the static type checking. - IO primitives are "native" functions, that is: closure preloaded into the environment and defined by means of an AST node that can be instantied only by invokations to these functions.
- At the moment,
Proj
on tuples and list operators are not functions! They are simple expressions, and then they cannot be used as higher-order functions or passed in pipe. Again, that's motivated by the static type checking. This will be updated with the future introduction of generics.
-
Hexadecimal integers
-
Global Declarations
-
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
-
Generics
-
Uncurried functions definitionsMultiple-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