[JoBullet]

Today I learned you can have (almost) arbitrary placed numeric placeholders(they are skipped while parsing though):
All of these are valid:

Code:

0b_10_1
0x_1DEAD
1_3_4_5
1_2.1_e-4

And as a added bonus, here's (pseudo) yacc grammar for these:

Code:

digit: [0-9]
hex: [a-fA-f0-9]
boolean: 0b[01_]+
integer: {digit}({digit}|_)*
hexadec: ({digit}|(0x)?)({hex} | '_')*
float: {digit}({digit} | '_')*\.{digit}({digit} | '_')*(e(-)?{digit}*)?