26 text {* \solution{ex:scancmts} *}

    27 

    28 ML {*

    29 val any = Scan.one (Symbol.not_eof);

    30 

    31 val scan_cmt =

    32   let

    33     val begin_cmt = Scan.this_string "(*" 

    34     val end_cmt = Scan.this_string "*)"

    35   in

    36    begin_cmt |-- Scan.repeat (Scan.unless end_cmt any) --| end_cmt 

    37    >> (enclose "(**" "**)" o implode)

    38   end

    39 

    40 val scan_all =

    41   Scan.finite Symbol.stopper (Scan.repeat (scan_cmt || any)) 

    42     >> implode #> fst 

    43 *}

    44 

    45 text {*

    46   By using @{ML_text "#> fst"} in the last line, the function 

    47   @{ML scan_all} retruns a string instead of a pair. For example:

    48 

    49   @{ML_response [display] "scan_all (explode \"foo bar\")" "\"foo bar\""}

    50 

    51   @{ML_response [display] "scan_all (explode \"foo (*test*) bar (*test*)\")" 

    52                           "\"foo (**test**) bar (**test**)\""}

    53 

    54 *}

    55