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Fixes #18583. ## Problem Several stdlib collection types compute the separator for `$` using `result.len > 1`, where `result` starts as the opening bracket (`"["` or `"{"`). This breaks when a collection element type has a `$` that returns an empty string: `result.len` stays at 1 after the first item contributes nothing, so the separator is never inserted for subsequent items. ```nim import std/deques type Test = object proc `$`(x: Test): string = "" echo [Test(), Test()].toDeque # prints [] — expected [, ] ``` ## Fix Replace the length check with an explicit `first` flag in all affected modules: `deques`, `heapqueue`, `lists`, `critbits`, and `strtabs`. ## Tests Regression tests added to `tdeques`, `theapqueue`, and `tlists` using a local type whose `$` returns `""`. All three test files pass with `nim c -r`. ## Notes I work with Claude as a co-processor. I'm 56, came to programming late, and this is genuinely how I learn and contribute. I understand what I'm submitting, but I didn't write it alone. If your project prefers human-only contributions, just say so and I'll close without friction. --------- Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>