parser-actions

#!/usr/bin/env tclkit8.6
#
# parser-actions.tcl
#
# Many parser generators allow code to be associated with the grammar rules and
# executed as the rules are recognized.  This script is a helper program to allow 
# action templates to be associated with [Parser Tools] peg grammar rules.
#
# When the peg parser returns the AST, it is executed as a tcl script.  This
# allows the names of the PEG rules to be direclty used as parser actions.  Each
# parser rule corrosponds to a proc (or method) of the parser.  In the grammer there
# are many rules which share the same code, specifically many non-terminal rules whose 
# value is the concatenated values of their child rules and leaf rules whose values
# are the underlying string or token that the rule matched.
#
# This proc allows the grammer file to "declare" the type of a rule in a following
# comment.  The rule type is then associated with a template for that type and the
# method is declared with the rule/action name and the code from the template.
#
 proc parser-actions { file actions } {
    set reply {}
    foreach line [split [read [open $file]] \n] {
	switch -regexp -matchvar match $line {
	    { *([a-zA-Z0-9_]+)[ \t]*<-[^;]*; *# *action ([a-zA-Z0-9_]+)[ \t]*} {
		append reply [string map [list %action [lindex $match 1]]	\
		    [dict get $actions [lindex $match 2]]] \n
	    }
	    { *([a-zA-Z0-9_]+)[ \t]*<-}	  { set action [lindex $match 1] }
	    {; *# *action ([a-zA-Z0-9_]+)[ \t]*$} {
		append reply [string map [list %action $action] 		\
		    [dict get $actions [lindex $match 1]]] \n
	    }
	}
    }

    set reply
 }

 set parser [lindex $argv 0]	;# A [Parser Tools] peg file w/annotations in comments.
 set action [lindex $argv 1]	;# A file containing a dict of template procs.

 puts [parser-actions $parser 				\
	 [regsub -all -line -- {((^[ \t]*)|([ \t]+))#.*$} [read [open $action]] { }]]