feat(sl): add --list flag for available vehicles

README.md

@@ -177,6 +177,7 @@ $ sl -s 0.1       # You do not
 | `-w` | `--whistle` | Sound the whistle as the train or ship passes |
 | `-s` | `--speed` | Animation speed multiplier, 0.1–20 (default: 1.0) |
 | | `--no-color` | Disable colors (`NO_COLOR` is also honored) |
+| | `--list` | List the available vehicles with a one-line description and exit |
 | `-v` | `--version` | Show version information |
 | `-h` | `--help` | Show help message |
 

sl

@@ -176,6 +176,14 @@ class Train:
         "c51": C51,
     }
 
+    # One-line descriptions for --list
+    DESCRIPTIONS = {
+        "classic": "the classic steam locomotive, no surprises",
+        "small": "a small locomotive for narrow terminals",
+        "d51": "D51 locomotive (Japanese style), pulls coal cars with -l",
+        "c51": "C51 locomotive, the -c engine",
+    }
+
     # Wheel animation: (row index, pattern, 4-frame cycle). Each cycle entry
     # must be the same width as the pattern it replaces.
     WHEEL_SPEC = {
@@ -348,6 +356,15 @@ class Vessel:
         "tug": TUG,
     }
 
+    # One-line descriptions for --list
+    DESCRIPTIONS = {
+        "galleon": "three-masted pirate galleon, flapping Jolly Roger, "
+                   "rubber-duck figurehead",
+        "steamer": "sternwheel steamer whose paddle wheel actually turns",
+        "sloop": "a racing sloop for narrow terminals",
+        "tug": "harbor tug in three-quarter perspective, travels diagonally",
+    }
+
     SIDE_VIEW = ("galleon", "steamer", "sloop")   # ride the drawn sea
     PERSPECTIVE = ("tug",)                        # travel their drawn angle
 
@@ -1038,11 +1055,19 @@ def main():
                              'clamped to 0.1-20 (default: 1.0)')
     parser.add_argument('--no-color', action='store_true',
                         help='disable colors (NO_COLOR is also honored)')
+    parser.add_argument('--list', action='store_true',
+                        help='list the available vehicles and exit')
     parser.add_argument('-v', '--version', action='version',
                         version=f'sl version {__version__}')
 
     args = parser.parse_args()
 
+    if args.list:
+        descriptions = {**Train.DESCRIPTIONS, **Vessel.DESCRIPTIONS}
+        for name in sorted(Train.TRAINS) + sorted(Vessel.VESSELS):
+            print(f"{name:<8} {descriptions[name]}")
+        return
+
     # Determine what rolls out (or sets sail)
     if args.type:
         craft = args.type