examples: structs_enums_for.ne demo

A small platformer scaffold that exercises every recent language
feature in one place:

- \`struct Player { ... }\` with u8 and bool fields
- \`enum Direction { Up, Down, Left, Right }\`
- \`enum AnimFrame { Idle, Run1, Run2 }\`
- \`for i in 0..4 { ... }\` looping over a fixed-size array
- Struct field assignment and reads
- Enum variant assignment

Compiles through the default IR codegen and links cleanly.

https://claude.ai/code/session_01W6eQFStA66EuMKHUFo2rx3

examples/structs_enums_for.ne

@@ -0,0 +1,80 @@
+// Demonstrates struct types, enums, and for loops.
+//
+// A small "platformer" scaffold: the player has a position, velocity,
+// and animation state held in a struct, enums describe directions and
+// animation phases, and a for loop iterates over an array of stationary
+// enemies each frame.
+//
+// Compile with the default IR codegen:
+//   nescript build examples/structs_enums_for.ne
+
+game "StructsDemo" { mapper: NROM }
+
+// Named constants for the four cardinal directions. Each variant is
+// a u8 value equal to its declaration order (Up=0, Down=1, etc.).
+enum Direction { Up, Down, Left, Right }
+
+enum AnimFrame { Idle, Run1, Run2 }
+
+// A struct bundles related state into a single variable. Only u8 /
+// i8 / bool fields are allowed in v0.1 — no nesting, arrays, or u16.
+struct Player {
+    x: u8,
+    y: u8,
+    vx: u8,
+    vy: u8,
+    facing: u8,   // Direction enum value
+    frame: u8,   // AnimFrame enum value
+    alive: bool,
+}
+
+var player: Player
+
+// A small fixed-size array of enemy x-positions. In a real game this
+// would be an array of structs once those are supported.
+var enemies_x: u8[4] = [32, 80, 160, 208]
+var enemy_y: u8 = 100
+
+const SPEED: u8 = 1
+
+on frame {
+    // Initialize the player once on the very first frame.
+    if player.alive == false {
+        player.x = 120
+        player.y = 112
+        player.facing = Down
+        player.frame = Idle
+        player.alive = true
+    }
+
+    // Read controls and update position. Velocities are u8 so we
+    // treat them as signed by adding/subtracting SPEED.
+    if button.left {
+        player.x -= SPEED
+        player.facing = Left
+    }
+    if button.right {
+        player.x += SPEED
+        player.facing = Right
+    }
+    if button.up {
+        player.y -= SPEED
+        player.facing = Up
+    }
+    if button.down {
+        player.y += SPEED
+        player.facing = Down
+    }
+
+    // Draw the player — the IR codegen allocates the OAM slot.
+    draw Smiley at: (player.x, player.y)
+
+    // And each enemy, using a for loop over the array.
+    for i in 0..4 {
+        draw Smiley at: (enemies_x[i], enemy_y)
+    }
+
+    wait_frame
+}
+
+start Main