haskell - Parsec parser failed on many1 and manyTill combinators -


i have faced unclear behavior of parsec parsers, want parsre strings same

>  <cdid> 1  >  <mol weight> 270.2369  >  <formula> c15h10o5  >  <log_er_rba> -0.36  >  <activity> 1

i wrote parser

 parseproperties =                skipmany1 newline         char '>' >> spaces >> char '<'          propname <- many1 (noneof ">")         char '>'         newline         propvalue <- many1 (noneof "\n")         return (propname,propvalue)

this parser excellently parse 1 item, , able parse several:

parsetest (count 5 parseproperties) "\n>  <cdid>\n1\n\n>  <mol weight>\n270.2369\n\n>  <formula>\nc15h10o5\n\n>  <log_er_rba>\n-0.36\n\n>  <activity>\n1\n\n"

results

 [("cdid","1"),("mol weight","270.2369"),("formula","c15h10o5"),("log_er_rba","-0.36"),("activity","1")]

nevertheless found no ways parse random numbers of properties. if try 

parsetest (many1 parseproperties) "\n>  <cdid>\n1\n\n>  <mol weight>\n270.2369\n\n>  <formula>\nc15h10o5\n\n>  <log_er_rba>\n-0.36\n\n>  <activity>\n1\n\n"

or

parsetest (manytill parseproperties (try eof)) "\n>  <cdid>\n1\n\n>  <mol weight>\n270.2369\n\n>  <formula>\nc15h10o5\n\n>  <log_er_rba>\n-0.36\n\n>  <activity>\n1\n\n"

parser failed 

parse error @ (line 17, column 1): unexpected end of input expecting new-line or ">"

but, if use anychar parser, not failed.

parsetest (manytill anychar (try eof)) "\n>  <cdid>\n1\n\n>  <mol weight>\n270.2369\n\n>  <formula>\nc15h10o5\n\n>  <log_er_rba>\n-0.36\n\n>  <activity>\n1\n\n"  "\n>  <cdid>\n1\n\n>  <mol weight>\n270.2369\n\n>  <formula>\nc15h10o5\n\n>  <log_er_rba>\n-0.36\n\n>  <activity>\n1\n\n"

the parseproperties parser executed many times in example until eof encountered. problem parseproperties not consume trailing whitespace in example, after parsing last tag, remaining string "\n\n", not trigger termination condition, since not end of input. causes parseproperties attempted again, consumes whitespace fails when trying eat '>'.

try modifying parsetest following

test = "\n>  <cdid>\n1\n\n>  <mol weight>\n270.2369\n\n>  <formula>\nc15h10o5\n\n>  <log_er_rba>\n-0.36\n\n>  <activity>\n1\n\n"  parsetest (manytill parseproperties $ try (skipmany newline >> eof)) test

this trys stripping preceding whitespace before checking if @ end of input.


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