fix(binary_tree): read trees passed back in as flat arrays - #977
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make_tree(5, make_tree(4, None, None), None) failed with "make_tree expects binary tree for left (expected binary tree, got ARRAY)". A tree is the list [entry, left, right]. make_tree builds it as a PAIR chain, but when a program passes it back in, py-slang and js-slang both flatten a proper list into one 3-element ARRAY. is_tree and the accessors walked every tree with pair_head/pair_tail, which on an ARRAY read elements 0 and 1 as head and tail, so the flattened tree was rejected. Trees are now read by readTreeNode, which reads an ARRAY by index and a PAIR chain by walking it, and requires exactly three elements. The old ARRAY test built nested 2-element arrays, which neither evaluator produces; it is replaced by tests using the real flat shape. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Problem
After #976, building a tree from another tree fails:
The same happens in Source:
make_tree(5, make_tree(4, null, null), null).A tree is the list
[entry, left, right], andmake_treebuilds it as a PAIR chain. When a program passes that tree back into the module, py-slang (pythonToModule) and js-slang (sourceToModule) both flatten a proper list into a single 3-elementARRAY.is_treeand the accessors walked every tree withpair_head/pair_tail. On anARRAYthose read elements 0 and 1, so the "tail" of[4, None, None]wasNoneand the tree was rejected.This bug predates #976. It was hidden because
make_treeused to fail earlier, on its entry argument.Fix
A new helper,
readTreeNode, reads a tree node into its three elements. It reads anARRAYby index and walks a PAIR chain, and requires exactly three elements either way.is_tree,entry,left_branchandright_branchall use it.Tests
The old "round-tripped as
ARRAY" test built nested 2-element arrays, which neither evaluator produces, so it passed while the real case failed. It is replaced by tests using the flat shape:is_treeaccepts flat trees, including a flat tree nested inside anotheris_treerejects arrays that don't have 3 elements, and flat trees with non-tree branchesmake_treeaccepts a flat tree as a branch (the reported case)entry/left_branch/right_branchread a flat tree by positionThe three positive tests fail on master and pass with this change. binary_tree has 23/23 passing, and
tscand lint are clean.Related
plotly's
add_fields_to_data(behindnew_plot) also walks a list with pair operations, and reads a flatARRAYas a single pair. It likely has the same bug. Not addressed here.🤖 Generated with Claude Code