Server IP : 85.214.239.14 / Your IP : 3.139.93.168 Web Server : Apache/2.4.62 (Debian) System : Linux h2886529.stratoserver.net 4.9.0 #1 SMP Tue Jan 9 19:45:01 MSK 2024 x86_64 User : www-data ( 33) PHP Version : 7.4.18 Disable Function : pcntl_alarm,pcntl_fork,pcntl_waitpid,pcntl_wait,pcntl_wifexited,pcntl_wifstopped,pcntl_wifsignaled,pcntl_wifcontinued,pcntl_wexitstatus,pcntl_wtermsig,pcntl_wstopsig,pcntl_signal,pcntl_signal_get_handler,pcntl_signal_dispatch,pcntl_get_last_error,pcntl_strerror,pcntl_sigprocmask,pcntl_sigwaitinfo,pcntl_sigtimedwait,pcntl_exec,pcntl_getpriority,pcntl_setpriority,pcntl_async_signals,pcntl_unshare, MySQL : OFF | cURL : OFF | WGET : ON | Perl : ON | Python : ON | Sudo : ON | Pkexec : OFF Directory : /proc/3/root/proc/self/root/usr/share/doc/libparse-recdescent-perl/examples/ |
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#!/usr/bin/perl -ws # THE COMMONEST REASON FOR WANTING LEFT RECURSION use strict; use Parse::RecDescent; $::RD_HINT = 1; sub Parse::RecDescent::evalop { $_[0][0] = $_[0][$_+1](@{$_[0]}[0,$_+2]) for map 2*($_-1), 1..@{$_[0]}/2; return $_[0][0]; } my $parse = Parse::RecDescent->new(<<'EndGrammar'); main: expr /\Z/ { $item[1] } | <error> expr: <leftop:term add_op term> { evalop($item[1]) } add_op: '+' { sub { $_[0] += $_[1] } } | '-' { sub { $_[0] -= $_[1] } } term: <leftop:factor mult_op factor> { evalop($item[1]) } mult_op: '*' { sub { $_[0] *= $_[1] } } | '/' { sub { $_[0] /= $_[1] } } factor: number | '(' expr ')' { $item[2] } number: /[-+]?\d+(\.\d+)?/ EndGrammar while (<DATA>) { print "$_ = ", $parse->main($_), "\n"; } while (print "> " and defined($_=<>)) { print "= ", $parse->main($_), "\n"; } __DATA__ 2+3 2*3 +1-1+1-1+1-1+1-1+1 7*7-6*8 121/(121/11)/121*11 1/(10-1/(1/(10-1)))