An Erlang implementation of the Kaleidoscope language from the LLVM tutorial.
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README.md

kalerl

Description

An Erlang implementation of the Kaleidoscope language from the LLVM tutorial. It's not a straight port as it targets BEAM, the Erlang VM, instead of native code. The project is a work in progress for the purpose of learning how to generate code targeting BEAM.

The name is pronounced "Kal-Earl," like Kal-el's redneck cousin who's really into compilers.

Dependencies

  • rebar
  • make
  • erlando (automatically downloaded and built by rebar)

Build

To build the kalerl compiler just run make.

$ make

This will place the kalerl executable in the bin subdirectory.

Use

The kalerl compiler can only take one parameter, the file to compile. For example:

$ ./bin/kalerl test/add.kalerl

This will generate a BEAM file in the same directory as the source file. In this case it will be test/add.beam. From here, the BEAM file can be used just like any other; all functions are exported by default.

$ cd test
$ erl
Eshell V7.2  (abort with ^G)
$ 1> l(add).
{module,add}

The above moves to the test directory, starts the Erlang shell, and loads the add BEAM file just built. To call a function:

$ 2> add:add(3.0).
5.0

Also, all kalerl modules export a main/0 function that executes all the top level expressions.

$ 3> add:main().
5.0

Language Differences

There are a few difference between kalerl and Kaleidoscope as defined by the LLVM tutorial. The most obvious is there is no REPL in kalerl; it assumes reading and writing from files.

One major deviation from the original Kaleidoscope language is the lack of mutability. BEAM/Erlang doesn't support it (mostly, kinda), so it doesn't make sense for kalerl to either. This means kalerl remains a functional language. Because of the lack of mutability, the var/in construct in Kaleidoscope becomes a let/in and kalerl does not implement an assignment operator. An example of a kalerl let/in:

let x = 3 + 4 * 5 in
let y = x + 7 in
...

Another difference is the handling of externs. kalerl doesn't handle calling out to C functions; instead it supports calling into Erlang modules. To accomplish that the language syntax changed to support designating the external module name. For example:

extern foo(a) in bar

declares that there is a function foo/1 in module bar. After this declaration, kalerl code can call foo/1 like any other kalerl function and it will do the right thing.