extracts the first token in front of a string
fronttoken("Hello World",Token,RestString)
fronttoken(String,Token,RestString) (i,x,x)
string(String) (i) string to be separated
string(Token) (x) first Token contained in String
string(RestString) (x) String without its leading white spaces characters and
Token
Fronttoken() skips all white space characters (blanks,tabs) and separates from the
resulting string the first valid token. The remainder is matched with RestString. A valid
token is either a variable or name
readln(Input), % e.g. enter "3+5", "4*6" fronttoken(Input,T1,,R1), fronttoken(R1,Op,T2), str_int(T1,I1),str_int(T2,I2), Expr =.. [Op,I1,I2], Sum is Expr, write(Sum),nl.
A runtime error occurs if the arguments belong to the wrong domain.
prolog-process, client-server, object
frontchar , str_char , frontchar ,
prologtoken , concat , str_len