question: public REProgram compile ( String pattern ) throws RESyntaxException { this . pattern = pattern ; len = pattern . length ( ) ; idx = 0 ; lenInstruction = 0 ; parens = 1 ; int [ ] flags = { NODE_TOPLEVEL } ; expr ( flags ) ; if ( idx != len ) { if ( pattern . charAt ( idx ) == ')' ) { syntaxError ( "Unmatched close paren" ) ; } syntaxError ( "Unexpected input remains" ) ; } char [ ] ins = new char [ lenInstruction ] ; System . arraycopy ( instruction , 0 , ins , 0 , lenInstruction ) ; return new REProgram ( parens , ins ) ; }
target:  Compiles a regular expression pattern into a program runnable by the pattern matcher class 'RE'.