Bran

A strongly-typed language with type inference running on Erlang VM, influenced by OCaml.

Requirements

For usage

• Erlang/OTP 17.3

For build

• OCaml 4.02.1
• Menhir 20140422
• Spotlib 2.5.0
• OMake 0.9.8.6-0.rc1

For test

• OUnit2 2.0.0

Building from source

$ omake

Installation

1. Execute make at liberl directory to compile Erlang sources used by compiled Bran modules.

$ cd liberl
$ make

2. Copy this directory or create a symbolic link to installation destination.

$ ln -s /home/yourname/bran /opt/local/bran

3. Add path of the bin directory to command line path. (environment variable PATH, etc.)

# .bashrc, etc.
export PATH=/opt/local/bran/bin:$PATH

4. Set environment variable BRAN_LIBS to the lib directory including signature files of Bran.

# .bashrc, etc.
export BRAN_LIBS=/opt/local/bran/lib

5. Add path of the liberl/ebin directory, including Erlang modules, to environment variable ERL_LIBS.

# .bashrc, etc.
export ERL_LIBS=/opt/local/bran/liberl/ebin:$ERL_LIBS

6. OK, let's try bran command.

$ bran

Usage

# compile
$ ./bran fib.br

# use as Erlang module
$ erl
...
1> fib:fib(10).
89

ToDo

• Data types
  • Map
  • Option
  • Reference
  • Exception
  • Binary
  • Process
• Type system
  • Records
  • Variants
  • Polymorphic type
• Syntax
  • Pattern matching
  • Exception handling
  • Labeled arguments and optional arguments
  • Message passing
• Compilation
  • Optimization
  • Executable file generation (escript)
• Library
  • Standard library
  • Obj module
  • OTP
• Tools
  • Interactive shell
  • Source browsing support
  • Build tool support (rebar)
• Build
  • Installation
  • Using packaging tools (OPAM, etc.)

Syntax

Files

• .bri (interface file)
• .br (implementation file)

Data Types

• unit
• bool
• int
• float
• char
• string
• list (empty lists must be specified type. for example: ([] : int list))
• bitstring

Comment

# comment

Literals

Atom

@atom
@Atom
@atom_ok
@Atom_ok
@"atom"
@"a t o m"
@"*a+t-o/m!?* :-@"

String

• On Bran, String is not a list of character type data. string and char list are different types.
• Escape sequences are the same as one of Erlang.

"string"
"42"
"hello, world!\n"
"\052"
"\x00\xff"

Character

• Character literals are single quote characters.

'0'
'a'
'Z'
'\n'
'\052'
'\xff'

Bitstring

Basically bitstring syntax is the same as one of Erlang. See Bit Syntax Expressions.

<<42>>
<<"abc">>
<<1,17,42:16>>
<<123/int-native>>
<<123/unsigned-big-integer>>
<"abc"/utf8>>

Integer

• Erlang's base#value is base r value (ex. 16rff). Because # is used by comment in Bran.
• Integer has any number of digits.

42
042 # -> 42
2r101
16r1f

Float

2.3
2.3e3
2.3e-3
7.000e+00

List

[]
[1]
[1, 2, 3]
[1, 2, 3,]

Tuple

(1, "a")

Array

[||]
[|1|]
[|1, 2, 3|]
[|1, 2, 3,|]

Variable bindings

var x = 1

Function

Definition

# Top level
def [rec] f x ... = [block] 

# Local
def [rec] f x ... = [block] in ...

# Circular reference
def [rec] f x ... = ...
and f x ... = ...

Top level definition starts at start of line.

def f x y = x + y

In function definition, definition must be indented and end with in. Indent size must be spaces more than one.

def f x =
  def f' x' =
    ...
  in
  f' x

signature (.bri):

def f : int -> int -> int

Call

f x y         # Call function "f" with "x" and "y" arguments
f x $ g y z   # => f x (g y z)  Haskell's "$"

External functions

.bri:

external print_bool : bool -> unit = "bran_lib_pervasives:print_bool"

Calling Erlang functions

use Erlang.eval : string -> string.

var result = Erlang.eval "ok."

Conditional

Conditional expression syntax is:

if [bool-exp] then [block] end
if [bool-exp] then [block] else [block] end
if [bool-exp] then [simple-exp] else [simple-exp]

"end" can be omitted when blocks have only an simple expression (literals, field access, array access, type constructor with no arguments and expression with parentheses).

Examples:

if x then
  print_string "true"
  true
end

if x then
  print_string "true"
  true
else
  print_string "false"
  false
end

if x then true else false

if x then true
else false

if x then
  true
else
  false

Loop

for i = 1 to max do
  ...
end

Exception handling

try [exp] with [pattern] end

Example:

try
  ...
with
  | Not_found -> ...
  | e -> raise e
end

Monad

perform
  x1 <- action1
  x2 <- action2
  action3 x1 x2
  return x1
end