factor/library/platform/native/parser.factor

! :folding=indent:collapseFolds=1:

! $Id$
!
! Copyright (C) 2004 Slava Pestov.
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IN: parser
USE: arithmetic
USE: combinators
USE: errors
USE: kernel
USE: lists
USE: logic
USE: namespaces
USE: stack
USE: strings
USE: words
USE: vocabularies
USE: unparser

! The parser uses a number of variables:
! line - the line being parsed
! pos  - position in the line
! use  - list of vocabularies
! in   - vocabulary for new words
!
! When a token is scanned, it is searched for in the 'use' list
! of vocabularies. If it is a parsing word, it is executed
! immediately. Otherwise it is appended to the parse tree.

: parsing? ( word -- ? )
    dup word? [
        "parsing" swap word-property
    ] [
        drop f
    ] ifte ;

: parsing ( -- )
    "cross-compiling" get [
        t "parsing" word set-word-property
    ] unless ; parsing

: <parsing "line" set 0 "pos" set ;
: parsing> "line" off "pos" off ;
: end? ( -- ? ) "pos" get "line" get str-length >= ;
: ch ( -- ch ) "pos" get "line" get str-nth ;
: advance ( -- ) "pos" succ@ ;

: ch-blank? ( -- ? ) end? [ f ] [ ch blank? ] ifte ;
: skip-blank ( -- ) [ ch-blank? ] [ advance ] while ;
: ch-word? ( -- ? ) end? [ f ] [ ch blank? not ] ifte ;
: skip-word ( -- ) [ ch-word? ] [ advance ] while ;

: ch-dispatch? ( -- ? )
    #! Hard-coded for now. Make this customizable later.
    #! A 'dispatch' is a character that is treated as its
    #! own word, eg:
    #!
    #! "hello world"
    #!
    #! Will call the parsing word ".
    ch "\"" str-contains? ;

: (scan) ( -- start end )
    skip-blank "pos" get
    end? [
        dup
    ] [
        ch-dispatch? [ advance ] [ skip-word ] ifte "pos" get
    ] ifte ;

: scan ( -- str )
    (scan) 2dup = [ 2drop f ] [ "line" get substring ] ifte ;

: parse-word ( str -- obj )
    dup "use" get search dup [
        nip
    ] [
        drop str>fixnum
    ] ifte ;

: parsed| ( obj -- )
    #! Some ugly ugly code to handle [ a | b ] expressions.
    >r nreverse dup last* r> swap set-cdr swons ;

: expect-] ( -- )
    scan "]" = not [ "Expected ]" throw ] when ;

: parsed ( obj -- )
    over "|" = [ nip parsed| expect-] ] [ swons ] ifte ;

: number, ( num -- )
    str>fixnum parsed ;

: word, ( str -- )
    [
        parse-word dup parsing? [ execute ] [ parsed ] ifte
    ] when* ;

: (parse) <parsing [ end? not ] [ scan word, ] while parsing> ;

: parse ( str -- code )
    #! Parse the string into a parse tree that can be executed.
    f swap (parse) nreverse ;

: eval ( "X" -- X )
    parse call ;

! Used by parsing words
: ch-search ( ch -- index )
    "pos" get "line" get rot index-of* ;

: (until) ( index -- str )
    "pos" get swap dup succ "pos" set "line" get substring ;

: until ( ch -- str )
    ch-search (until) ;

: until-eol ( -- str )
    "line" get str-length (until) ;

: next-ch ( -- ch )
    end? [ "Unexpected EOF" throw ] [ ch advance ] ifte ;