Add xeus-haskell kernel to conformance tests (#39)

Seventh (and final) of 7 xeus kernels requested in #30. Adds Haskell language snippets.

Key changes:
- Build xeus-haskell from source using Pixi (not yet on conda-forge)
- Add 15-minute timeout for build-from-source jobs

Note: xeus-octave (PR #36) uses Xvfb for X11 requirements.

Author: rgbkrk

.github/workflows/conformance.yml

@@ -14,7 +14,7 @@ jobs:
   test-kernel:
     name: Test ${{ matrix.kernel.name }}
     runs-on: ubuntu-latest
-    timeout-minutes: 10
+    timeout-minutes: 15
     strategy:
       fail-fast: false
       matrix:
@@ -86,6 +86,16 @@ jobs:
           - name: xeus-lua
             install: micromamba install -y xeus-lua -c conda-forge
             kernel-name: xlua
+          - name: xeus-haskell
+            install: |
+              curl -fsSL https://pixi.sh/install.sh | bash
+              export PATH="$HOME/.pixi/bin:$PATH"
+              git clone https://github.com/jupyter-xeus/xeus-haskell /tmp/xeus-haskell
+              cd /tmp/xeus-haskell
+              pixi run -e default prebuild
+              pixi run -e default build
+              pixi run -e default install
+            kernel-name: xhaskell
 
     steps:
       - uses: actions/checkout@v4

src/snippets.rs

@@ -53,6 +53,7 @@ impl LanguageSnippets {
             "c++" | "cpp" => Self::cpp(),
             "sql" => Self::sql(),
             "lua" => Self::lua(),
+            "haskell" => Self::haskell(),
             _ => Self::generic(&lang),
         }
     }
@@ -292,6 +293,27 @@ xcpp::display(h);"#,
         }
     }
 
+    fn haskell() -> Self {
+        // Haskell functional language
+        Self {
+            language: "haskell".to_string(),
+            print_hello: "putStrLn \"hello\"",
+            print_stderr: "import System.IO; hPutStrLn stderr \"error\"",
+            simple_expr: "1 + 1",
+            simple_expr_result: "2",
+            incomplete_code: "let x =",
+            complete_code: "let x = 1",
+            syntax_error: "let let",
+            input_prompt: "-- Haskell stdin varies by kernel",
+            sleep_code: "import Control.Concurrent; threadDelay 2000000",
+            completion_var: "testVariableForCompletion",
+            completion_setup: "let testVariableForCompletion = 42",
+            completion_prefix: "testVariableFor",
+            display_data_code: "putStrLn \"no rich display\"",
+            update_display_data_code: "-- Haskell doesn't support update_display_data",
+        }
+    }
+
     /// Generic fallback for unknown languages
     fn generic(language: &str) -> Self {
         Self {