Reproduce

Please include this information when filing a bug report:

herbie shell --seed 2020270 
(FPCore (a b_2 c)
  :name "quad2p (problem 3.2.1, positive)"
  :precision binary64
  (/ (+ (- b_2) (sqrt (- (* b_2 b_2) (* a c)))) a))

Backtrace

repr-of: arity mismatch; the expected number of arguments does not match the given number expected: 3 given: 1 arguments...: 0		L	C
binary-op-with-repr	/data/pavpan/nightlies/herbie/egg-taylor/src/programs.rkt	270	0
convert-try-/	/data/pavpan/nightlies/herbie/egg-taylor/src/core/simplify.rkt	47	0
differentiate-exprs	/data/pavpan/nightlies/herbie/egg-taylor/src/core/simplify.rkt	39	0
(unnamed)	/opt/racket-7.8/collects/racket/contract/private/arrow-higher-order.rkt	375	33
get-batch	/data/pavpan/nightlies/herbie/egg-taylor/src/core/taylor.rkt	18	0
terms-for-coeffs	/data/pavpan/nightlies/herbie/egg-taylor/src/core/taylor.rkt	76	2
approximate	/data/pavpan/nightlies/herbie/egg-taylor/src/core/taylor.rkt	51	0
location-do-multiple	/data/pavpan/nightlies/herbie/egg-taylor/src/programs.rkt	110	0
taylor-alt	/data/pavpan/nightlies/herbie/egg-taylor/src/mainloop.rkt	132	0
for-loop	/data/pavpan/nightlies/herbie/egg-taylor/src/mainloop.rkt	174	7
gen-series!	/data/pavpan/nightlies/herbie/egg-taylor/src/mainloop.rkt	167	0
run-iter!	/data/pavpan/nightlies/herbie/egg-taylor/src/mainloop.rkt	353	0
run-improve	/data/pavpan/nightlies/herbie/egg-taylor/src/mainloop.rkt	372	0
(unnamed)	/data/pavpan/nightlies/herbie/egg-taylor/src/sandbox.rkt	72	6
run	/opt/racket-7.8/share/pkgs/profile-lib/main.rkt	39	2
profile-thunk	/opt/racket-7.8/share/pkgs/profile-lib/main.rkt	9	0
(unnamed)	/opt/racket-7.8/collects/racket/engine.rkt	42	24