Use refs for non-simple chained comparisons

[STRd6]

Use a ref in non-simple chained comparisons so not to repeat evaluations of complex expressions.

f1(x) < f2(x) < f3(x) < f4(x)

let ref
f1(x) < (ref = f2(x)) && ref < (ref = f3(x)) && ref < f4(x)

[edemaine]

Other settings where we should use refs (please add to list if you encounter any):

• { foo[x+y] } → { [x+y]: foo[x+y] } ({x[y]} shorthand for {[y]: x[y]} #284)
• a().{b,c} → { b: a().b, c: a().c } (Object glob patterns obj.{a,b} #327)
• f()@x → f().x.bind(f()) (x@y and @@x bind shorthand, plus JSX fixes #506)
• Thick pipes
• (count[f()] ?= 0)++ ( Allow assignments and update operators within assignments and update operators ++/-- #353)

[JayXon]

I see that this issue is tagged as efficiency, but I think this is not just efficiency, but a correctness issue, since an expression could have side effect, see the examples in #1341 and #1344

[JayXon]

it seems #1344 is still not fixed, can we keep this open or reopen #1344?