Specification

\[\begin{array}{l} \\ \begin{array}{l} t_0 := \tan x \cdot \tan x\\ \frac{1 - t_0}{1 + t_0} \end{array} \end{array} \]

(FPCore (x)
 :precision binary64
 (let* ((t_0 (* (tan x) (tan x)))) (/ (- 1.0 t_0) (+ 1.0 t_0))))

double code(double x) {
	double t_0 = tan(x) * tan(x);
	return (1.0 - t_0) / (1.0 + t_0);
}

real(8) function code(x)
    real(8), intent (in) :: x
    real(8) :: t_0
    t_0 = tan(x) * tan(x)
    code = (1.0d0 - t_0) / (1.0d0 + t_0)
end function

public static double code(double x) {
	double t_0 = Math.tan(x) * Math.tan(x);
	return (1.0 - t_0) / (1.0 + t_0);
}

def code(x):
	t_0 = math.tan(x) * math.tan(x)
	return (1.0 - t_0) / (1.0 + t_0)

function code(x)
	t_0 = Float64(tan(x) * tan(x))
	return Float64(Float64(1.0 - t_0) / Float64(1.0 + t_0))
end

function tmp = code(x)
	t_0 = tan(x) * tan(x);
	tmp = (1.0 - t_0) / (1.0 + t_0);
end

code[x_] := Block[{t$95$0 = N[(N[Tan[x], $MachinePrecision] * N[Tan[x], $MachinePrecision]), $MachinePrecision]}, N[(N[(1.0 - t$95$0), $MachinePrecision] / N[(1.0 + t$95$0), $MachinePrecision]), $MachinePrecision]]

\begin{array}{l}

\\
\begin{array}{l}
t_0 := \tan x \cdot \tan x\\
\frac{1 - t_0}{1 + t_0}
\end{array}
\end{array}

Reproduce

herbie shell --seed 2023271 
(FPCore (x)
  :name "Trigonometry B"
  :precision binary64
  (/ (- 1.0 (* (tan x) (tan x))) (+ 1.0 (* (tan x) (tan x)))))

Please file a bug report with this information.

Backtrace

length: contract violation expected: list? given: 8000		L	C
(unnamed)	/home/nightlies/herbie/arb-support/egg-herbie/main.rkt	111	2
egraph-run	/home/nightlies/herbie/main/src/core/egg-herbie.rkt	502	0
egraph-run-rules	/home/nightlies/herbie/main/src/core/egg-herbie.rkt	559	0
run-egg	/home/nightlies/herbie/main/src/core/egg-herbie.rkt	288	0
simplify-batch	/home/nightlies/herbie/main/src/core/simplify.rkt	15	0
(unnamed)	/usr/share/racket/collects/racket/contract/private/arrow-higher-order.rkt	379	33
find-preprocessing	/home/nightlies/herbie/main/src/preprocess.rkt	11	0
run-improve!	/home/nightlies/herbie/main/src/mainloop.rkt	325	0
get-alternatives/report	/home/nightlies/herbie/main/src/sandbox.rkt	149	0
(unnamed)	/home/nightlies/herbie/main/src/sandbox.rkt	245	6
(unnamed)	/usr/share/racket/pkgs/profile-lib/main.rkt	40	10
profile-thunk	/usr/share/racket/pkgs/profile-lib/main.rkt	9	0
(unnamed)	/usr/share/racket/collects/racket/engine.rkt	42	24