# LibTmux.FSharp.Chain.start

- **Module:** LibTmux.FSharp
- **Package:** LibTmux.FSharp
- **Language:** F#
- **Kind:** function
- **Source:** https://github.com/libtmux/libtmux-dotnet/blob/cf34b255c896d19a97e7d7fabea58609c916012d/src/LibTmux.FSharp/Hierarchy.fsi#L409
- **Page:** https://libtmux.org/en/fsharp/latest/reference/libtmux-fsharp-chain-start/

```
val start: server: LibTmux.Server -> TmuxChain
```

Starts an empty chain against a server.

## Examples

Create a session from F# records in one call: the first window is the one tmux makes with the session, and each split goes beside the pane before it. Add a window with a command chain, then read through a handle whose commands each get five seconds. Use Linux or macOS with Git, tmux 3.2a or newer, .NET SDK 10.0.303, and the .NET 8 and 10 runtimes. In an empty directory, fetch the documented library revision:

```console
$ git clone https://github.com/libtmux/libtmux-dotnet.git libtmux-source && \
  git -C libtmux-source checkout --detach cf34b255c896d19a97e7d7fabea58609c916012d
```

Save this complete consumer setup as global.json:

[Source example](https://github.com/libtmux/libtmux-dotnet/blob/cf34b255c896d19a97e7d7fabea58609c916012d/global.json).

```json
{
  "sdk": {
    "version": "10.0.303",
    "rollForward": "disable",
    "allowPrerelease": false
  },
  "test": {
    "runner": "Microsoft.Testing.Platform"
  }
}
```

Save this complete consumer setup as NuGet.config:

[Source example](https://github.com/libtmux/libtmux-dotnet/blob/cf34b255c896d19a97e7d7fabea58609c916012d/examples/api/NuGet.config).

```xml
<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <packageSources>
    <clear />
    <add key="libtmux-source" value="libtmux-source/artifacts/api-example-packages" />
    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" />
  </packageSources>
  <packageSourceMapping>
    <clear />
    <packageSource key="libtmux-source">
      <package pattern="LibTmux" />
      <package pattern="LibTmux.*" />
    </packageSource>
    <packageSource key="nuget.org">
      <package pattern="*" />
    </packageSource>
  </packageSourceMapping>
</configuration>
```

Save this complete consumer setup as Example.fsproj:

[Source example](https://github.com/libtmux/libtmux-dotnet/blob/cf34b255c896d19a97e7d7fabea58609c916012d/examples/api/fsharp/Example.fsproj).

```xml
<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFrameworks>net8.0;net10.0</TargetFrameworks>
    <LangVersion>10.0</LangVersion>
    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
    <DisableImplicitFSharpCoreReference>true</DisableImplicitFSharpCoreReference>
    <DisableImplicitLibraryPacksFolder>true</DisableImplicitLibraryPacksFolder>
  </PropertyGroup>
  <ItemGroup>
    <Compile Include="Program.fs" />
    <PackageReference Include="FSharp.Core" Version="[10.1.303]" />
    <PackageReference Include="LibTmux.FSharp" Version="[0.0.0-alpha.20]" />
  </ItemGroup>
</Project>
```

Save this complete program as Program.fs. It creates a private server with LibTmux.Server.CreateOwnedAsync; use! disposes owned scopes after success, cancellation or failure. The F# facade has no separate server constructor.

[Source example](https://github.com/libtmux/libtmux-dotnet/blob/cf34b255c896d19a97e7d7fabea58609c916012d/examples/LibTmux.FSharp.Examples/Programs/BuildSession.fs).

```fsharp
// fsharp-snippet: BuildSession
open System
open System.Threading
open LibTmux
open LibTmux.FSharp

let runAsync () =
    task {
        use deadline = new CancellationTokenSource(TimeSpan.FromSeconds 20.)
        let token = deadline.Token

        let options =
            ServerConnectionOptions(
                SocketName = "fsharp-build-session-" + Guid.NewGuid().ToString("N"),
                ConfigurationFile = "/dev/null"
            )

        use! owned = options |> Server.createOwned token

        // Describe the session, then create it in one call: the first window is
        // the one tmux makes with the session, and each split goes beside the
        // pane before it, sized in cells or as a share of the space it splits.
        let dev =
            { SessionSpec.named "dev" with
                Windows =
                    [
                        { WindowSpec.named "editor" with
                            Command = Some "exec sleep 60"
                        }
                        { WindowSpec.named "logs" with
                            Command = Some "exec sleep 60"
                            Splits =
                                [
                                    { SplitSpec.empty with
                                        Direction = Some PaneDirection.Right
                                        Size = Some(SplitSize.Percent 30)
                                        Command = Some "exec sleep 60"
                                    }
                                    { SplitSpec.empty with
                                        Size = Some(SplitSize.Cells 8)
                                        Command = Some "exec sleep 60"
                                    }
                                ]
                        }
                    ]
            }

        let! session = owned.Value |> Server.newSession token dev

        // A chain runs in one tmux invocation; each step acts on what the one
        // before made.
        let! _ =
            owned.Value
            |> Chain.start
            |> Chain.newWindow session "watch"
            |> Chain.splitLeftRight
            |> Chain.sendLine "exec sleep 60"
            |> Chain.run token

        // Every command through this handle, and the handles taken from it,
        // gives tmux five seconds.
        let bounded = owned.Value |> Server.within (TimeSpan.FromSeconds 5.)
        let! windows = bounded |> Server.windows |> Query.list token

        for window in windows do
            let! panes = window |> Window.panes |> Query.list token
            printfn "%s: %d panes" window.Name panes.Count
    }

runAsync().GetAwaiter().GetResult()
// endfsharp-snippet
```

Build the exact source packages and the saved consumer, then run both supported frameworks. The local package feed prevents an unrelated published package from satisfying the restore. Each program checks its result and exits unsuccessfully after an unhandled error:

```console
$ export NUGET_PACKAGES="$PWD/packages" && \
  dotnet restore libtmux-source/src/LibTmux.FSharp/LibTmux.FSharp.fsproj --locked-mode && \
  dotnet pack libtmux-source/src/LibTmux/LibTmux.csproj \
    --configuration Release --no-restore -p:ContinuousIntegrationBuild=true \
    --output "$PWD/libtmux-source/artifacts/api-example-packages" && \
  dotnet pack libtmux-source/src/LibTmux.FSharp/LibTmux.FSharp.fsproj \
    --configuration Release --no-restore -p:ContinuousIntegrationBuild=true \
    --output "$PWD/libtmux-source/artifacts/api-example-packages" && \
  dotnet restore Example.fsproj --configfile NuGet.config && \
  dotnet build Example.fsproj --configuration Release --no-restore --warnaserror && \
  export LIBTMUX_TMUX="$(command -v tmux)" && \
  export TMUX_TMPDIR=/tmp/libtmux-dotnet-dev && \
  mkdir -p "$TMUX_TMPDIR" && \
  unset TMUX TMUX_PANE && \
  dotnet bin/Release/net8.0/Example.dll && \
  dotnet bin/Release/net10.0/Example.dll
```

Expected program output from each framework:

```text
editor: 1 panes
logs: 3 panes
watch: 2 panes
```

## Parameters

- `server` (`LibTmux.Server`)

## Raises

- [`System.InvalidOperationException`](https://learn.microsoft.com/dotnet/api/system.invalidoperationexception): The server handle has no connection.