1 files changed, 90 insertions, 0 deletions
diff --git a/src/pex/block.zig b/src/pex/block.zig
new file mode 100644
index 0000000..3ae690e
--- /dev/null
+++ b/src/pex/block.zig
@@ -0,0 +1,90 @@
+const std = @import("std");
+const NonTerminal = @import("../non-terminal.zig");
+const Rule = @import("../rule.zig");
+const Node = @import("node.zig");
+
+const Self = @This();
+
+id: usize,
+heads: std.ArrayListUnmanaged(*Node) = .empty,
+
+pub fn compile(
+    non_terminal: *NonTerminal,
+    node_pool: *std.heap.MemoryPool(Node),
+    allocator: std.mem.Allocator
+) !Self {
+    var self: Self = .{ .id = non_terminal.id };
+
+    for (non_terminal.rules()) |*rule| {
+        try self.heads.append(allocator, try compile_variant(rule, node_pool));
+    }
+
+    return self;
+}
+
+pub fn deinit(self: *Self, allocator: std.mem.Allocator) void {
+    for (self.heads.items) |head| {
+        head.deinit();
+    }
+    self.heads.deinit(allocator);
+    self.* = undefined;
+}
+
+pub fn clone(
+    self: *const Self,
+    allocator: std.mem.Allocator,
+    node_pool: *std.heap.MemoryPool(Node),
+) !Self {
+    var self_clone = Self{
+        .id = self.id,
+        .heads = try .initCapacity(allocator, self.heads.items.len),
+    };
+    errdefer self_clone.deinit(allocator);
+
+    for (self.heads.items) |head| {
+        try self_clone.heads.append(allocator, try head.clone(node_pool));
+    }
+
+    return self_clone;
+}
+
+fn compile_variant(
+    rule: *Rule,
+    node_pool: *std.heap.MemoryPool(Node),
+) !*Node {
+    const first = blk: {
+        for (rule.items, 0..) |item, index| {
+            switch (item) {
+                .terminal, .non_terminal => break :blk index,
+                .epsilon => {},
+            }
+        }
+
+        break :blk rule.items.len;
+    };
+
+    if (first == rule.items.len) {
+        return try Node.create(.{ .@"return" = void{} }, node_pool);
+    }
+
+    const head = switch (rule.items[0]) {
+        .terminal => |c| try Node.create(.{ .@"check" = c }, node_pool),
+        .non_terminal => |id| try Node.create(.{ .@"call" = id }, node_pool),
+        .epsilon => unreachable,
+    };
+
+    var current = head;
+    for (rule.items[1..]) |item| {
+        const node = switch (item) {
+            .terminal => |c| try Node.create(.{ .@"check" = c }, node_pool),
+            .non_terminal => |id| try Node.create(.{ .@"call" = id }, node_pool),
+            .epsilon => continue,
+        };
+        current.next = node;
+        current = node;
+    }
+
+    current.next = try Node.create(.{ .@"return" = void{} }, node_pool);
+
+    return head;
+}