HelenOS sources

lc_increase       160 uspace/app/sbi/src/lex.c 	{ lc_increase,	"+=" },
lc_increase       483 uspace/app/sbi/src/lex.c 			lex->current.lclass = lc_increase;
lc_increase       106 uspace/app/sbi/src/p_expr.c 	case lc_increase:
HelenOS homepage, sources at GitHub