# attempt to write parser in forth
# bootstrapping is done using preparse.pf


# REQUIREMENTS:
# * needs to be pre-emptable
# * needs to be re-enterable
# * needs to be able to be fed by character source

# special characters
: open?       0x28 = ; # (
: close?      0x29 = ; # )
: quote?      0x22 = ; # "
: backslash?  0x5c = ; # \
: newline?    0x0d = ; # \n
: comment?    0x23 = ; # #
: space?      0x20 = ; # space
: tab?        0x08 = ; # tab
: whitespace? >r r newline? r space? or r> space? or ;


# state
variable parser-in
variable parser-out
10 variable! base

: next-char parser-in pop ;


# eof handler
: eof	    ` eof throw ;


# converters

# numbers
: range?     >r dup 0 >= swap r> < and ;

: a-z?       0x61 - 26 range? ;
: A-Z?       0x41 - 26 range? ;
: 0-9?       0x30 - 10 range? ;
: >upper     dup a-z? if 0x20 - then ;
: digit      dup 0-9? if 0x30 - leave then 
	     >upper
	     dup A-Z? if [ 10 0x41 - ]L + leave then
	     -1 ;

: base?      base @ range? ;


: >base      split? if >r swap base @ * r> + swap pass >base then ;
: >number    ' digit map 0 swap >base ;


# other

: skip-ws    next-char dup whitespace? if drop pass skip-ws then ;
: read-char  skip-ws ;

# what about REQUIRING a whitespace before and after lists?  this will
# make the grammar simpler, and also the parser, but no longer
# compatible with s-expressions