Röda 0.12, length 19 (Cracked by @KritixiLithos)

PCRE:

^{(\|[^\/#\s]*){8}$ 

Sample output (n=4):

[1, 2, 3, 4][8, 7, 6, 5][9, 10, 11, 12][16, 15, 14, 13] 

Original code:

{|n|seq(0,n-1+n%2)|push([{|i|seq(n*i+1,n*i+n)}(_)],[{|j|seq(n*j+n,n*j+1,step=-1)}(_)])|head(n)} 

Try it online!

Röda 0.12, length 19 (Cracked by @KritixiLithos)

PCRE:

^{(\|[^\/#\s]*){8}$ 

Sample output (n=4):

[1, 2, 3, 4][8, 7, 6, 5][9, 10, 11, 12][16, 15, 14, 13] 

Original code:

{|n|seq(0,n-1+n%2)|push([{|i|seq(n*i+1,n*i+n)}(_)],[{|j|seq(n*j+n,n*j+1,step=-1)}(_)])|head(n)} 

Try it online!

Röda 0.12, length 19

PCRE:

^{(\|[^\/#\s]*){8}$ 

Sample output (n=4):

[1, 2, 3, 4][8, 7, 6, 5][9, 10, 11, 12][16, 15, 14, 13] 

I'm not sure if it's fair to use a language that not many here can use... Is there a rule about this?

Röda 0.12, length 19 (Cracked by @KritixiLithos)

PCRE:

^{(\|[^\/#\s]*){8}$ 

Sample output (n=4):

[1, 2, 3, 4][8, 7, 6, 5][9, 10, 11, 12][16, 15, 14, 13] 

Original code:

{|n|seq(0,n-1+n%2)|push([{|i|seq(n*i+1,n*i+n)}(_)],[{|j|seq(n*j+n,n*j+1,step=-1)}(_)])|head(n)} 

Try it online!