add ruby 3.1.0

runtimes/default.nix

@@ -15,4 +15,5 @@ args: {
     "gawk-awk" = import ./gawk-awk.nix args;
     "openjdk11_headless-java" = import ./openjdk11_headless-java.nix args;
     "zig" = import ./zig.nix args;
+    "ruby" = import ./ruby.nix args;
 }

runtimes/ruby.nix

@@ -0,0 +1,57 @@
+{pkgs, piston, ...}:
+let 
+    pkg = pkgs.ruby_3_1; # ruby 3.1 stable from unstable channel
+in piston.mkRuntime {
+    language = "ruby";
+    version = pkg.version;
+
+    aliases = [
+        "ruby3"
+        "rb"
+    ];
+
+    run = ''
+    ${pkg}/bin/ruby "$@"
+    '';
+
+    # Run the following command to test the package:
+    # $ ./piston test ruby
+    tests = [
+        # standard output test
+        (piston.mkTest {
+            files = {
+                "test.rb" = ''
+                    puts("OK");
+                '';
+            };
+            args = [];
+            stdin = "";
+            packages = [];
+            main = "test.rb";
+        })
+        # args test
+        (piston.mkTest {
+            files = {
+                "test.rb" = ''
+                    puts $*;
+                '';
+            };
+            args = ["OK"];
+            stdin = "";
+            packages = [];
+            main = "test.rb";
+        })
+        # stdin test
+        (piston.mkTest {
+            files = {
+                "test.rb" = ''
+                    print Kernel.gets;
+                '';
+            };
+            args = [];
+            stdin = "OK";
+            packages = [];
+            main = "test.rb";
+        })
+    ];
+}