AWS Lambda Elm

gulpfile.js

var gulp = require('gulp'),
    $ = require('gulp-load-plugins')({lazy:true, camelize: true}),
    join = require('path').join;

/*
 * SETUP
 */

function path(rel) {
    return join(__dirname, rel);
}

var config = {
    paths: {
        src: {
            backend: path('/Main.elm'),
            lambdaBackend: path('/Wrapper.js')
        },
        dist: {
            filename: 'elm.js',
            lambdaFilename: 'index.js',
            archive: 'archive.zip',
            backend: path('/out/')
        }
    }
};

/*
 * JS
 */

gulp.task('elm-init', $.elm.init);

gulp.task('build-backend', ['elm-init'], function() {
    return gulp.src(config.paths.src.backend)
        .pipe($.elm())
        .pipe($.rename(config.paths.dist.filename))
        .pipe(gulp.dest(config.paths.dist.backend))
});

/*
 * DEPLOY
 */
 
gulp.task('deploy', ['build-backend'], function() {
    var elm = config.paths.dist.backend + config.paths.dist.filename;
    return gulp.src([elm, config.paths.src.lambdaBackend])
        .pipe($.concat(config.paths.dist.lambdaFilename))
        .pipe($.uglify())
        .pipe($.zip(config.paths.dist.archive))
        .pipe($.awslambda('lambda_name', {region: 'us-east-1'}))
        .pipe(gulp.dest(config.paths.dist.backend));
});

Main.elm

module Main where

import Signal


type alias Message =
    { operation : String
    , message : String
    }


port request : Signal Message


port response : Signal Message
port response = Signal.map handleRequest request


handleRequest : Message -> Message
handleRequest m =
    case m.operation of
        "PING" ->
            { m | operation = "PONG" }

        x ->
            { m | operation = "UNKNOWN" }

package.json

{
  "name": "elm-lambda-demo",
  "dependencies": {},
  "devDependencies": {
    "gulp": "3.9.0",
    "gulp-awslambda": "0.2.3",
    "gulp-concat": "2.6.0",
    "gulp-elm": "0.2.0",
    "gulp-load-plugins": "1.1.0",
    "gulp-rename": "1.2.2",
    "gulp-uglify": "1.5.1",
    "gulp-zip": "3.0.2"
  }
}

Wrapper.js

var backend = Elm.worker(Elm.Backend.Main, {
    request: {
        operation: '',
        message: ''
    }
});

exports.handler = function(event, context) {
    backend.ports.response.subscribe(function(response) {
        context.succeed(response);
    });

    try {
        backend.ports.request.send({
            operation: event.operation,
            message: event.message
        });
    } catch (e) {
        context.fail('Bad Request: invalid input');
    }
};

what event triggers the lambda call?

Related work and shameless Plug: https://github.com/ktonon/elm-serverless (pun intended)