I've doodled this idea independently a couple of times, but I see a few issues:
1. Line breaks throw a monkey wrench in the works (though it might be reasonable to prohibit line breaks within { ... }).
2. In many contexts, it can be tough to count spaces. :)
3. Sometimes it's nice to tabulate similar lines of code using extra spaces, and in those cases this feature would be a minor annoyance, since it would force some subexpressions to bail out to parentheses.
// Horizontal layout interferes:
var wargle = 2 * x + 0.03 * y + 200;
var tricennarious = 13 * x + 0.4 * y + 50;
// Fix:
var wargle = 2 * x + (0.03 * y) + 200;
var tricennarious = 13 * x + (0.4 * y) + 50;
var wargle = 2 * x + 0.03 * y + 200;
var tricennarious = 13 * x + 0.4 * y + 50;
Adding tabulation in addition to whitespace precedence would end up making expressions even more loose and baggy than otherwise. The writer would have to count spaces, but it's fairly clean when reading.
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Thanks for the pointers! I'm going to go look at those now.