I setup the simple ZIO App from zio.dev.
val myAppLogic =
for {
_ <- putStrLn("Hello! What is your name?")
name <- getStrLn
_ <- putStrLn(s"Hello, ${name}, welcome to ZIO!")
} yield ()
When running in/with Intellij it works as expected.
However running it with mill it doesn't.
nbszmbp012:zio-scala-camunda-bot mpa$ mill server.run
[27/37] server.compile
[info] Compiling 1 Scala source to /Users/mpa/dev/Github/pme123/zio-scala-camunda-bot/out/server/compile/dest/classes ...
[info] Done compiling.
[37/37] server.run
Hello! What is your name?
Peter
name <- getStrLn is not executed.
Here is the build.sc
import mill._, scalalib._
object server extends ScalaModule {
def scalaVersion = "2.12.8"
def ivyDeps = Agg(
ivy"dev.zio::zio:1.0.0-RC10-1",
ivy"com.bot4s::telegram-core:4.3.0-RC1"
)
}
Did I miss something?
Mill runs, by default, in client-server mode. One of the consequences is, that build tasks can't consume the input stream.
Your given example needs to read from the process standard input. So, you have to explicitly tell mill to run in interactive mode with --interactive (or short -i).
$ mill -i server.run
[27/37] server.compile
[info] Compiling 1 Scala source to /tmp/zio-q/out/server/compile/dest/classes ...
[info] Done compiling.
[37/37] server.run
Hello! What is your name?
Peter
Hello, Peter, welcome to ZIO!
When invoked with the additional -i (before the task name), the ZIO app correctly reads from STDIN and prints the greeting.
Related
In the book, Programming in Scala 5th Edition, the author says the following for two classes:
Neither ChecksumAccumulator.scala nor Summer.scala are scripts, because they end in a definition. A script, by contrast, must end in a result expression.
The ChecksumAccumulator.scala is as follows:
import scala.collection.mutable
class CheckSumAccumulator:
private var sum = 0
def add(b: Byte): Unit = sum += b
def checksum(): Int = ~(sum & 0XFF) + 1
object CheckSumAccumulator:
private val cache = mutable.Map.empty[String, Int]
def calculate(s: String): Int =
if cache.contains(s) then
cache(s)
else
val acc = new CheckSumAccumulator
for c<-s do
acc.add((c >> 8).toByte)
acc.add(c.toByte)
val cs = acc.checksum()
cache += (s -> cs)
cs
whereas the Summer.scala is as follows:
import CheckSumAccumulator.calculate
object Summer:
def main(args: Array[String]): Unit =
for arg <- args do
println(arg + ": " + calculate(arg))
But when I run the Summer.scala file, I get a different error than what mentioned by the author:
➜ learning-scala git:(main) ./scala3-3.0.0-RC3/bin/scala Summer.scala
-- [E006] Not Found Error: /Users/avirals/dev/learning-scala/Summer.scala:1:7 --
1 |import CheckSumAccumulator.calculate
| ^^^^^^^^^^^^^^^^^^^
| Not found: CheckSumAccumulator
longer explanation available when compiling with `-explain`
1 error found
Error: Errors encountered during compilation
➜ learning-scala git:(main)
The author mentioned that the error would be around not having a result expression.
I also tried to compile CheckSumAccumulator only and then run Summer.scala as a script without compiling it:
➜ learning-scala git:(main) ./scala3-3.0.0-RC3/bin/scalac CheckSumAccumulator.scala
➜ learning-scala git:(main) ✗ ./scala3-3.0.0-RC3/bin/scala Summer.scala
<No output, given no input>
➜ learning-scala git:(main) ✗ ./scala3-3.0.0-RC3/bin/scala Summer.scala Summer of love
Summer: -121
of: -213
love: -182
It works.
Obviously, when I compile both, and then run Summer.scala, it works as expected. However, the differentiation of Summer.scala as a script vs normal file is unclear to me.
Let's start top-down...
The most regular way to compile Scala is to use a build tool like SBT/Maven/Mill/Gradle/etc. This build tool will help with a few things: downloading dependencies/libraries, downloading Scala compiler (optional), setting up CLASS_PATH and most importantly running scalac compiler and passing all flags to it. Additionally it can package compiled class files into JARs and other formats and do much more. Most relevant part is CP and compilation flags.
If you strip off the build tool you can compile your project by manually invoking scalac with all required arguments and making sure your working directory matches package structure, i.e. you are in the right directory. This can be tedious because you need to download all libraries manually and make sure they are on the class path.
So far build tool and manual compiler invocation are very similar to what you can also do in Java.
If you want to have an ah-hoc way of running some Scala code there are 2 options. scala let's you run scripts or REPL by simply compiling your uncompiled code before it executes it.
However, there are some caveats. Essentially REPL and shell scripts are the same - Scala wraps your code in some anonymous object and then runs it. This way you can write any expression without having to follow convention of using main function or App trait (which provides main). It will compile the script you are trying to run but will have no idea about imported classes. You can either compile them beforehand or make a large script that contains all code. Of course if it starts getting too large it's time to make a proper project.
So in a sense there is no such thing as script vs normal file because they both contain Scala code. The file you are running with scala is a script if it's an uncompiled code XXX.scala and "normal" compiled class XXX.class otherwise. If you ignore object wrapping I've mentioned above the rest is the same just different steps to compile and run them.
Here is the traditional 2.xxx scala runner code snippet with all possible options:
def runTarget(): Option[Throwable] = howToRun match {
case AsObject =>
ObjectRunner.runAndCatch(settings.classpathURLs, thingToRun, command.arguments)
case AsScript if isE =>
ScriptRunner(settings).runScriptText(combinedCode, thingToRun +: command.arguments)
case AsScript =>
ScriptRunner(settings).runScript(thingToRun, command.arguments)
case AsJar =>
JarRunner.runJar(settings, thingToRun, command.arguments)
case Error =>
None
case _ =>
// We start the repl when no arguments are given.
if (settings.Wconf.isDefault && settings.lint.isDefault) {
// If user is agnostic about -Wconf and -Xlint, enable -deprecation and -feature
settings.deprecation.value = true
settings.feature.value = true
}
val config = ShellConfig(settings)
new ILoop(config).run(settings)
None
}
This is what's getting invoked when you run scala.
In Dotty/Scala3 the idea is similar but split into multiple classes and classpath logic might be different: REPL, Script runner. Script runner invokes repl.
I have an Ammonite Script that I want to deliver in a JAR.
In another project I want to use this Script - but so far with no success.
I tried according to the documentation (sol_local_build.sc):
import $ivy.`mycompany:myproject_2.12:2.1.0-SNAPSHOT`, local_build
#main
def doit():Unit =
println(local_build.curl("http://localhost:8080"))
local_build.sc is in the Script I want to use.
This is the exception I get:
sol_local_build.sc:2: '.' expected but eof found.
^
The script must be compiled on the fly.
Put your script in a standard sbt project
inside a directory, example directory name: "test1"
Put your external script (example name: "script.sc")
// script.sc
println("Hello world!")
into the resource directory ("test1\src\main\resources\script.sc") of the test1 project
Publish the projekt local, i.e. sbt publishLocal
It is published to ".ivy2\local\default\test1_2.12\0.1-SNAPSHOT\ ... " directory.
Now you can use the following ammonite script "test.sc".
It reads the "script.sc" from the jar in the local ivy repository
and writes it to the local directory (must have read/write access) and then executes an external process,
which calls the scala "interpreter" and executes the script.
// test.sc
import $ivy.`default:test1_2.12:0.1-SNAPSHOT`
val scriptCode = scala.util.Try {scala.io.Source.fromResource("script.sc").mkString} getOrElse """Println("Script-file not found!")"""
println("*" * 30)
println(scriptCode)
println("*" * 30)
println()
java.nio.file.Files.write(java.nio.file.Paths.get("script.sc"), scriptCode.getBytes(java.nio.charset.StandardCharsets.UTF_8))
val cmd = Seq("cmd.exe", "/c", "scala", "script.sc")
val output = sys.process.Process(cmd).!!
println(output)
Executing the script the Ammonite REPL, you get:
******************************
// script.sc
println("Hello world!")
******************************
Hello world!
The script has no error handling and leaves the file in the running directory.
You can speed up the execution with the "-savecompiled" compiler switch, i.e
val cmd = Seq("cmd.exe", "/c", "scala", "-savecompiled", "script.sc")
An additional .jar file is created then in the running directory.
Scala Scripts are not really interpreted, but are compiled "under the hood"
as every normal Scala programm.
Therefor all code must be reachable during compile time
and you cannot call a function inside the other script from the jar-file!
But Ammonite has a buid in multi-stage feature.
It compiles one part, executes it and then compiles the next part!
Little improved ammonite-script.
It's not error free but runs.
Maybe there is better way to get the script out of the jar.
You should ask Li Haoyi!
// test_ammo.sc
// using ammonite ops
// in subdirectoy /test1
// Ammonite REPL:
// import $exec.test1.test_ammo
// # Ammonite-multi-stage
import $ivy.`default::test1:0.1-SNAPSHOT`
//import scala.util.Properties
import scala.sys.process.Process
val scriptFileName = "script.sc"
write.over(pwd/"test1"/scriptFileName, read(resource(getClass.getClassLoader)/scriptFileName))
val cmd = Seq("cmd.exe", "/c", "scala", scriptFileName)
val output = Process(cmd).!!
println(output)
#
import $exec.script // no .sc suffix
ppp() // is a function inside script.sc
script.sc inside resources folder of project
published local with "sbt publishLocal":
// script.sc
println("Hello world!")
def ppp() = println("Hello world from ppp!")
For completeness, I could solve my problem as follows:
Just create a Scala File in this project.
Copy the Script content in
an Object.
package mycompany.myproject
object LocalBuild {
def curl(..)...
}
Add the dependencies to your sbt file (e.g. ammonite.ops)
Use it like:
$ivy.`mycompany:myproject_2.12:2.1.0-SNAPSHOT`, mycompany.myproject.LocalBuild
#main
def doit():Unit =
println(LocalBuild.curl("http://localhost:8080"))
I have the following scala program that simply counts the words in a file:
package com.impatient
import java.util.Scanner
object Main extends App {
countWords()
def countWords(): Unit = {
val in = new Scanner(new java.io.File("C:\\tmp\\SampleText.txt"))
var wc = 0
while (in.hasNext()) {
var word = in.next()
wc += 1
println( wc + ". " + word)
}
in.close()
println("======================")
println(s"Total words: $wc")
}
def TestFunction(): Unit ={
println("Hello from test function!")
}
TestFunction()
}
When I execute this in intellij, either directly or via the sbt shell inside intellij, I get the following output:
mostly
positive:
======================
Total words: 309
Hello from test function!
So it correctly counts 309 words in the text file.
However if I try to execute the jar that I just compiled with intellij, directly, either via scala or sbt I get the following output:
λ scala .\impatientscala2_2.12-1.0.jar
======================
Total words: 0
Hello from test function!
So in this case, although the methods in Main are executed the wordcount is 0.
Why would be this the case? Is intellij referencing some other java libraries that standalone sbt or scala isn't? In that case why doesn't the Scanner fail?
Edit 1
I have cloned this repo to another PC to see what happens. And in that case I can observe the exact opposite, i.e.:
The program returns 0 word count when run from Intellij
When the jar is run directly with scala, it gives the current wordcount.
The 0 wordcount is due to not processing the while loop, as in.hasNext() returns nothing.
I found a workaround by using Paths.get from java.nio.file._.
//val in = new Scanner(new java.io.File("C:/tmp/SampleText.txt"))
val in: Scanner = new Scanner(Paths.get("C/tmp/SampleText.txt"))
This produces the correct jars on both PCs, when using Run | Sbt Task in Intellij, using SBT Shell in intellij, and using standalone SBT shell. If anyone can provide an explanation of why would java.io.File fail in certain setups that would be great.
I have a subproject in my build.sbt with a rather long setting for initialCommands, comprising a list of imports and some definitions. I'd like to test this as part of regular CI, because otherwise I won't notice breaking changes after refactoring code. It is not clear to me how to do so.
Just running sbt console doesn't seem to cut it, because there is always a "successful" exit code even when code doesn't compile.
Moving the code out into an object defined in a special source file won't help because I need the list of imports to be present (and I don't want to cakeify my whole code base).
Moving the code out into a source file and then loading that with :load also always gives a successful exit code.
I found out about scala -e but that does strange things on my machine (see the error log below).
This is Scala 2.12.
$ scala -e '1'
cat: /release: No such file or directory
Exception in thread "main" java.net.UnknownHostException: <my-host-name-here>: <my-host-name-here>: Name or service not known
You could generate a file and run it like any other test file:
(sourceGenerators in Test) += Def.task {
val contents = """object TestRepl {
{{}}
}""".replace("{{}}", (initialCommands in console).value)
val file = (sourceManaged in Test).value / "repltest.scala"
IO.write(file, contents)
Seq(file)
}.taskValue
I have a very simple scala program:
object TakeInputs {
def main(args: Array[String]) {
val name = readLine("What is your name?")
println(name)
}
}
When I try to run this with
sbt "project myproject" "run-main TakeInput"
it doesn't wait for user input and the program just finishes with
What is your name?null
as the output.
Is there a way to make sbt wait for user input (like what happens if "readLine" is run in sbt console)? I can provide the inputs as command line parameters but I have a lot of them and I would like to make the program more user-friendly by displaying messages indicating what the user should enter next. Thanks.
Add the following to your build.sbt
connectInput in run := true
From the sbt documentation in Configuring Input