PEG grammars in Tcl - simple example

This is the very simple example how to create PEG grammar and parse some text with it in Tcllib (I used Tcllib 1.4).

package require starkit
starkit::startup
package require pt::peg::from::peg
package require pt::peg::container
package require pt::peg::interp

set PEG {
PEG myapp (Exp)
    IfKw       <- 'i' 'f'                               ;
    ThenKw     <- 't' 'h' 'e' 'n'                       ;
    ElseKw     <- 'e' 'l' 's' 'e'                       ;
    OSp        <- ('\t' / '\n' / ' ')?                  ;
    Sp         <- ('\t' / '\n' / ' ')+                  ;
    Block      <- (Exp / 't') &';'                      ;
    Cond       <- 'c' / 'o'                             ;
    If         <- IfKw Sp Cond OSp ':' OSp Block        ;
    Exp        <- If                                    ;
END;
}

set CPEG [pt::peg::from::peg convert $PEG]
pt::peg::container cont
cont deserialize = $CPEG
set src "if c: if o:t;"
pt::peg::interp myint
myint use cont
puts [myint parset $src]

(I use startkit...)
This grammar is very simple (and non-realistic): it defines rules to parse nested 'if'-expression like this:

if c: if o: t;

OR

if CONDITION: if CONDITION: BLOCK;

where CONDITION is 'c' or 'o', BLOCK is another EXP (expression) or 't' followed by ';'; when blocks are nested, only one ';' is needed. Example has bugs (see Sp, OSp - Optional SPaces) but shows base tricks with PEG, for ex., PEG definition is loaded from variable, not imported from file, so you need for your App. not all Tcllib packages :) After running, you get:

c:\>tclkitsh.exe main.tcl
Exp 0 11 {If 0 11 {IfKw 0 1} {Sp 2 2} {Cond 3 3} {OSp 4 3} {OSp 5 5} {Block 6 11 {Exp 6 11 {If 6 11 {IfKw 6 7} {Sp 8 8}
{Cond 9 9} {OSp 10 9} {OSp 11 10} {Block 11 11}}}}}