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A lambda is applied to its argument before its body is simplified - #2156
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Rafael-SOWNet merged 1 commit intoOct 27, 2026
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Simplifying an application simplified the lambda first and put the argument into what came back. A simplified body treats its parameter as a number, as every symbol is one, so [[0, -1], [1, 0]] * u became [[0, -u], [u, 0]], and the vector [p, q] put in for u gave the matrix of vectors [[0, [-p, -q]], [[p, q], 0]] where the product is [-q, p]. A dot product written [1, 1]T * u gave [[[p, q], [p, q]]] for p + q. A lambda written in place is now applied to its argument first, and the result simplified. A lambda that only appears once its function part is simplified is applied as before. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_012sonx8iAspMiwRwokT1Ura
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October 27, 2026 10:40
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Fixes #2132.
A wrong answer: applying a lambda to a vector gave a matrix of vectors.
apply(lambda(u, [[0, -1], [1, 0]] * u), [p, q])[[0, [-p, -q]], [[p, q], 0]][-q, p]apply(lambda(u, [1, 1]T * u), [p, q])[[[p, q], [p, q]]]p + qCause.
Application.InnerSimplifysimplified the lambda first and then put the argument into what came back. A simplified body treats its parameter as a number, as every symbol is one, so[[0, -1], [1, 0]] * uhad already become[[0, -u], [u, 0]]by the time[p, q]went in.Fix. A lambda written in place is applied to its argument first, and the result is then simplified. A lambda that only appears once the function part is simplified is applied as before.
Checked:
LambdaCalculusTest, including a two-parameter lambda.apply(lambda(x, x * x), [1, 2])still simplifies to[1, 4]on this branch. That is #2141's elementwise power, which #2155 fixes.Found while reading Modenov's Problems in Geometry for #2131, whose rotation of a plane vector through π/2 is this lambda.
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https://claude.ai/code/session_012sonx8iAspMiwRwokT1Ura