EmbeddingGemma 2: an open, lightweight multimodal embedding model
deepmind.google·6d ago
AI Engineering
Lobsters·Aug 14·5 min read
Unexpected (to me) behaviour in Lisp sub-typing
TL;DR
Common Lisp's SBCL implementation exhibits unexpected behavior in array sub-typing, particularly when specializing simple arrays. This can lead to confusion during type-checking of struct instances.
✦ Why It Matters
Review your array type declarations in Common Lisp to avoid unexpected type-checking issues.
Key Takeaways
- Use explicit array creation to ensure correct type-checking.
- Be aware of how SBCL optimizes array storage.
- Understand the difference between simple-vectors and constrained types.
- Consult documentation for nuances in type behavior.
How It Works
In SBCL, arrays can be optimized during creation, leading to a representation that may not match the specified type. For example, an empty array is treated as a simple-vector, which complicates type-checking against constrained types like (unsigned-byte 16).
This optimization allows for efficient storage but requires developers to be explicit about types to avoid errors.