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# Description Because `and` and `or` are short-circuiting operations in Nushell, they must be compiled to a sequence that avoids evaluating the RHS if the LHS is already sufficient to determine the output - i.e., `false` for `and` and `true` for `or`. I initially implemented this with `branch-if` instructions, simply returning the RHS if it needed to be evaluated, and returning the short-circuited boolean value if it did not. Example for `$a and $b`: ``` 0: load-variable %0, var 999 "$a" 1: branch-if %0, 3 2: jump 5 3: load-variable %0, var 1000 "$b" # label(0), from(1:) 4: jump 6 5: load-literal %0, bool(false) # label(1), from(2:) 6: span %0 # label(2), from(4:) 7: return %0 ``` Unfortunately, this broke polars, because using `and`/`or` on custom values is perfectly valid and they're allowed to define that behavior differently, and the polars plugin uses this for boolean masks. But without using the `binary-op` instruction, that custom behavior is never invoked. Additionally, `branch-if` requires a boolean, and custom values are not booleans. This changes the IR to the following, using the `match` instruction to check for the specific short-circuit value instead, and still invoking `binary-op` otherwise: ``` 0: load-variable %0, var 125 "$a" 1: match (false), %0, 4 2: load-variable %1, var 124 "$b" 3: binary-op %0, Boolean(And), %1 4: span %0 # label(0), from(1:) 5: return %0 ``` I've also renamed `Pattern::Value` to `Pattern::Expression` and added a proper `Pattern::Value` variant that actually contains a `Value` instead. I'm still hoping to remove `Pattern::Expression` eventually, because it's kind of a hack - we don't actually evaluate the expression, we just match it against a few cases specifically for pattern matching, and it's one of the cases where AST leaks into IR and I want to remove all of those cases, because AST should not leak into IR. Fixes #14518 # User-Facing Changes - `and` and `or` now support custom values again. - the IR is actually a little bit cleaner, though it may be a bit slower; `match` is more complex. # Tests + Formatting The existing tests pass, but I didn't add anything new. Unfortunately I don't think there's anything built-in to trigger this, but maybe some testcases could be added to polars to test it. |
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This crate primarily drives the evaluation of expressions.
(Some overlap with nu-protocol)
- Provides
CallExt
Internal Nushell crate
This crate implements components of Nushell and is not designed to support plugin authors or other users directly.