META 2. A Syntax-Di .... cted Compiler Wr'iting 2.1What does u�vnta.K-directed mea.n? The Use of a. Compiler � 2.2. 2.3. Writing a Compiler Using Meta. • • • • • Th. Nature of Syntax Descriptions 2.4. •
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4. 4. 1. 4.2.
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,4.4. 4.5. 4.6. 4.7.
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TEST terms Sin,le Character T�st Multiple Character Te s t •
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. BLANK t e s t Assemb1y Language Tests I rtve ...t Pas s / Fa i 1 Discard Tokens · . Pr'odlJc t ion Ca.ll 4.8. N�sted levels of CHOICES 4.9. Svntix of TESTS 4.10. �
Coun��d Re,.�at ,. M�s5a.ge Oerlerating Terms Opti o'na. 1 CHq,I,C.ES' R,epea.t 'Term un t i l Fai 1 CALL T a,ce Contro 1 •
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Meta iitr,"MUltiPlt!:' ,Character Test •
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The SYnta.x of a META P ... ogram 3. Productions 0 • 3.1Choices 3.2. " ." " " T.rmlists 3.3. " . " . " Tests and Actions 3.4.
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17 18 19 19 20
21
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. C I-META .
I
'�', l \ i-I I
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... �dit.
is. e. ppodlJ,ct of Mal"'inchip Systems. 16 St. Jude Rd • • Mill Valle)', CA 94941. This manlJal is not int$nded as � prodlJct specificatio�. The d£'s.:ription of META tIIiv·u. in th. fill11' META.MET on the r·elea:;.e diskette fhal 1 in .11 events be corlsidel"'ed the final a.rbiter- on how META wOl"'ks. The PIJI"'Pose of this document is. to expla.in the that deta.il enou9h in co�pi1er compileI"' sYnta.x-directed definition of the 1a.n91Ja.ge ma.y be re.d and understood.
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META. 3.5 1Is.,,.. M.w'JaJ
. . . �
..
use of .. the actlJa 1
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....
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11
Webster
definws SYNTAX as:
t) A connect�d e 'w",e n t s
or
o�derly sYstem '
For our purposes. synta� means the underlying structure of a that specifies how the smallest items ("tokens") ar'!? combined UP statements and programs.
languag� to:, make
A
The
way
in
syntax-d irected com�iler is one that processes th.�input source and a descr'lption of val id sYr,ta>c f.)r the . fr�ge, t Co pe rfc.rrro t he d� s i r'e d f IJnC t i (,_ns'••"Jpheo.J_,the s Y'nt,a>� the inplJt SO'J . r'ce the in·PIJt SOIJrce c(.de does not c(lnf� the s·,"ntax
META is a language wi th which you describe the syntax of a tar�et language that language YOU wish to compile. and the aS5embl� code that should be generat�d for each part of the source code that matches th� sy�tax .description. Ttw Use of
�
which
or swr,twrt,:es.
words are put t0gether
or
clauses.
2)
u
harmonious arrang�ment o f p�rts to form phrases.
•
a
Compiler
usi�9 file that EDIT In practice. a user will create a text source s ource cod� to be compiled. The Compiler will read t�is the contains that statem'i'rlts larI9ua.ge ,assefl'lb1', s.)ur'ce file _nd cr'eate a file of fun,:tions. Contro)� is then pol.ssed. to ASM, wt!c,", desired the per-for'", fi�, wr·'ltes .a te:>
memQry.
prQ9.ra.;"and anY�'IJtor-(I!Jttni7�)
wi 11 cQf1'IPUe all modules. (1Tlain IJs.er The IJsing the above protess, and therl \&Ii11 !.:Ise tte LINK p.r·lj9r;,.ri'I. t,) 111ak€!. .an Ea·:h use"lbl
The
�3·) IJ r· c e f i 1 eo q�5emblv Code Fife Ril�cat"lble File E:.'_�J : IJtab 1 Ii' F'co9f·,'i.Ch
-1 practice� �. _�SM .'\ In
...
step
EDIT »
.,'I [
�
I] -i.-J rl.] _
COMPILE ),) LINK
»
RUN
compiler. while it is examining the source- code it is to compil�. and the run-time librOl.ry mOl.Y need set-up directions fro.'�our compiled c(lIje. Ke-�ping these rel.ated but seper-ately tim�d eventE-;\��M-in.lt""d_is the n".de.t pad .f compil •• wdbn9. rhe task t,!:!ps:
!-
of wr'iting
cc.mpi leI'"
",IOl.Y
the exact
be br-oken dClwn
2)
You must determine wh�t .assembly langua�e cod� in re�ponse t� the various syntax eleme�ts.
descr:ibe
You must write any r�n·time the ,:c.IT.-piled code.·
.."'
.
in'4t,,�fO:I11owin£l
You
�.
must
a
",,:,
1)
4)
syntax
subroufi�es fhat
is
will
to be gen�rated be
n�eded
by
You ITIIJSt deblJ9 a.rld ··thus validate YOIJr' cOITIPiler- and r-'.lrl-t:!m'Ie routines. This wil! a.ctu�1'y consume most of your effo�t.
The ",/our': ':(-i�pi ler: a.nd r'outines at �_"ca.l s: ;Jstlor -> S ·'Ir.l,ft'J.:d, a(ld a Pf'o9f'a". 1 09 1':: manlJa 1. $0(' t��'fTl�'Jfle el �'" m�nth� ,later ' that ma� �aintaln the com�iler. tt���b. You six will need explairlati·orf$ o� why s.:tff,ethin9 was d,:onGo tbe 'waY it WOl.S.
1htr'(ld;Jce YOU OAll'-att'Ja1Wo;k �ith META and •
...
:!··-ye
U
the
To write � compiler using META. vou will need a· very 900d understanding of assembly language pro�raming, the function of compiler s . and the ability to keep �eperate t.ime-related eve nt s coordin�ted. As a pOl.cka,e. a compiler includes Ol.ctions taken during the gener'ation of ttut. compi leI". during the e)�ecuti(ln of the cOITIPiler. Ol.nd during the execution of the compiled progrOl.lTI. In describing 50�e p.u' t (If a compiler', YOU may. set a META flag to allow SI)me option t,) be
3)
'.1]
t h e compiler �utom�tica" Y executes th • • s$9mbl�r. $0 trOl.osPOl.rent to th& Yser. Th� IJ".f" ·follows the pOl.tti.-r-n:
2. :3.
:; C"'�(".b;;p.� 'I]
is
f.'
-
'"-"
'-1 -
-
a" 4 ,\- .....
Th� Natur�
,.
" ':',ii1' .'
11£1/1-3,. $ us'. ... t1';HHHll ;"!;'
',_
of Syntax Descriptioo$
It is impossibl� to describe .ovthin9 a. compl�x ai � lao9uage in a sin91� definition. Thus the language is broken ioto �.veral pi�c�s. and seperate description. are given for each piece, and then a �mast.r description" is made that �ho�s how the pieces' fit tO�8th.r. Th� moi� comple}( the lant'llJa9�, the more levels of d'e$cripti(ln that mi!lht be tJsed.
,
)] I
,_
. l I
One approach that might be used is to start our definitions with the the smallest pieces and build UP fl"(lm ther·e. An-other' is. tel star·t l.&Iith overall program and break i t down into smaller and �maller piaces. Whichevel" approach YOU take depends 00 personal �refar�nce.
In this manualr the bottom-up appr�ach will be used. notbetause it is better, blJt bel:ause it allows the use .,f examples that a:,r:bS'Htflf)e.riJitl) th,- .... d"_ '",,":, ',\"
i), J
--j
L
!�
LJ
ex�"'d :�Q
de.::! 1 bi' 'rh� !:.mallest th i rl 9 s a cljIJIPiler' must r'f!a!:,(lnablv it··· s as '.&lith thir.gs smalle$t the gr·.)IJPS of I:har'acter's taken together an:' usually meanins in a lan9uage. For- example, almost all individual have that by prQ9ramming languages use indentifiers. or v'riable names, mad� UP II r-'J 1 es II fol" the se i ,je-nt 1 f i ers rrti ght be .�::·::pr·-:.s sed in IJser. The tt-Ie ·ensl ish: f.;o 1 'Cowed by none or ",,:ore 1 <:: tt&�s or dig i bi., """I.Jed A 1 et t-aor" by the first .:t.ar·actet· that is. n.:ot a let-ter' .:Ir a di9it. i$ art identifie .... _ _
I]
In META
vnu
I DENT IF IER
IDENTIFIER .
$
ACHR
.ANCHR .OTOI
could describe this with: ==
=
•
ACHR $
•
ANCHR
•
QTm(EN
ao identifier is � a letterfollowed by none or more letters or numbers (1J,a.k� it a sin:gle thU19 fr'om rlow i.Jrd (Thats. all, Fo1J($')
/
the The process of maki09 a c�mpile� with METAb�9ins wi�h de9�riblng pieces ' as thes
J Th� Synta.x of
-it.
META Pr'oilram
recursively defined 1�n9Uage. Each p�rt of it) i� dlfined META is � using sma.ller pieces. When we get to the small pieces. we find that of them are many defined by using the "hi�her level" piece�. It is like :a. cat chatsin9 its tail! eecaY,e of this. it i� necessa.ry to have an overall picture of META as Ii. language BEFORE the lan9ya�e may be explained. To aJe�uately do this. we will mak� "two passes" at the problem. The first descript i on of META is a simplified example. and is intended to gi�e .n overall picture. but not a good definitio� of each piece. When that has be e n d one, a mor·ft detailftd definition, of META wi 1 1 f I)1 1 ow.
\�I
:::. 1.
�
.
s"tr uc bJre
�
th'e IJCTIC A in META Language is statemftot is to arll)t�r. lio\n9IJa���, A .. �'prodIJction dli'fines thi:' syntol.x fIH· ... sin91e "piece'&":of YOIJr' c.ver-al1 sYnta>�. ir. terms .:at even ml)re fUrldamerlta 1 pieces. A· ...t...P'T'lf'ied sYrtta>( description of a production is:
I�
fundamenta 1
The
,;.e.r:�_u,ctior. is tCI META who1,t a
PRODUCTION
=
This breaks down as
PRODUCTION :: "=
follows:
an equal
.
,
(end of . ,
,�one
';
The syntax known as i s defin44 as be�n� si9n
the syntax
{,:ho ices> .'
"::
followed by
called choices
�he definition) .
', �,
ir. wr-itten point �fir.terest is that the META compi ler is Se:. writ'tef'vin META. itself is prodlJct i on META abc.ve The understand ,h ow the line:
I L
PRODUCTION
U., 1
flts
=
its own d e f i n i ti o n of
�=
•
(c�oice5>
production!
�;
META. if y.:I!J
.\
, META 3;,5 IJ.er t1&.nual
2. -a3� -! :
IJ
Th&
Choices
syntax specifies that desc�l'ptio�s " ' b� used. must
sy�tax i s�'
CHOICES
=
$
C
'1
a of one and only A simple definition �f
of 1 is t : : h '�I i ': � s:;.
one
)
.,. .
;
everytin9 Which introduces two new terms. The braces ( ) indicate that to b� consid�r�d a single term. The $ indicates that is them inside the next sin91e term is to be repeated as many times as it is match&d. CHOICES
=
The
svr.tax c.a 11l!'d CHOICES
The sYntax followed
by none
or
i
So
dl?f i rllE'd
: ��� _,..,....t-;<"�_
more -
u
)
The
The
(end
char·acter· syntax
of
the
:
definition
of
CHOrCES)
-
IJ lU u. 'd
, .......... ---
-6'"
oiiE-
�l
,'�
:3.3.
Termlists
A definition TERMLIST
TERMLIST «
test)
-=
=
of
( (test)
:
i ..
<�ction) )
( (test)
:
(';i..:ti.)n)
)
The e.Ynta::� called TERMLIST
}
is
;
Either the syntax of (test) or if n�t that, then the syntax of <�ction). followed by �one
i]
)]
$
or
mor�
choice of the syntax of
.)1"
End of the defintio� of (ter�list). A or (ac t ion)
.,--'"!'
If the fi�st term in a '.rmlist fails. then Control is ��tY,..ned to the .:h.:d.:e s 1 evel .)f syntax fortes-ting the n&xt choice. if any. H(tw ...�v .... r·, if any term except the first term fails. then a SYNTAX ERROR is gerrei"ated. This is be ,:alJse d .... te':ted. and ar, &rror messa.ge wi 11 be each termlist is desi9��d to handle a particular "phrase" and if part of i t doesn�t match. then there is an error. This may be ov�r�idden by placin9 the character ":fl before any term, forcing a failyre ret�rn as if t hat term were the first term. As an example . � numeric literal migh t be defined by:
NLIr
=
$
.blank
.nehr
$
.nchr
,
01Jlfleri-:
mtl,l)i.(,jn� t
wt.ic'h states' that any 1 eadin9 blanks ac:-", tc. be skipped, the .:har�ctef' 1 iter:al. ,lfc�t . also.
is rIot a .. ::'<;�'a ""Jm�r.i(
d.i�i b
the te ....
df9it::th�n
any
-
-..
,"
and
,
·1
the!"! ' if n'JIT"'�l"ic
di9iJ$
..
11ETA3.�;US�r-· ,
- � .!;
-�1. II
[1 i]
4.
A i-I.., !J _
T •• ts and Actio"
Some example ..'
=
TEST
TEXT
-=
/..
..'
t�sts are:
.( s 1:>
examples =
'(
=
"
.
TEXT"
.r..
;
,�
Test for· the existence o f a sin�"';�"'.;,·, character. We used this above with ': t� te�t for an equal si�n \j
II
•.
��.;:.J.. '
_
of actions are: ;
Generate output code frQm the pattern given in the string literal. An ��ampl�: t�\bl\subroutine/ur S�nd the string litera l to as. a.me · ss�ge TEXT "PLOCompi 1 er- 'J1. 0".
the
coosol�
•
".
Thes� ul1'lird--derinitions" .a.re intended to give YOU a. fr· .. m, of r�.er·enc:it desc:,..ipti.;,r,5 that fol1Qw. YOIJ �ccur .. t. a.rid detai led f'H' the 'n',.;,r-e' Sh�'Jl � oot' e:x:pect to uoderS·tand exactl ...... how th� f.it together- "'it.' ttds P010t.
IJ
U�
-,���,:.
Test for the exist�nc. of a 5tring of characters� such as a keyword. "READ" would test for the ke�word READ bei�9 next in �he i�put str.am�
,IJ,. IJ
::�
M�nlJal
The syntax elements called (test) and
CODE
)]
:"�,
":s-
l
!:!
;i1
i��'
Meta. TEST terms
4. 1. I !\ 'i'
fJ n
Sin,'e
seTEST
\,�l I�
, rUf'l )]
[1
4.2.
Multiple Chaf'acter
_
U .,
(str-in9
4.3.
=
liter-01.1)
Cho1. ... a.cter Test with Delimite ... Check
Multiple
MCTESTO = �?
"
BLANK test
META tests? incl'Jdin, all of the a1)o� 1 istedtest's, skip InaflY Ijs�d slJt;h as those .anY lea.,din9 bla.'nks that ... ... e present, while o the ... s. do not. ttl. follolaJir'9 test- wil" pass iF a �·laflk is tokens. build to the from removed be will the next chara�te ... , and if so. the blank input stream. !
. BU�N"�
11
!J
TQst
, a ' multipl� characte ... · t�5t. _,�nY le � ding specifi .. s 1i � eral � . str'ins lnplJt .1ar.ks a ... e skIPped. and then the 1 iteral 15 tested a9�.,!���' th� r em o ved from the input a ... e characte ... s the m�tches, it st ... eam. �If a.re blanks lea.ding the �nly not, st ... eam, and the tes t pass .. s. IF If upper ca.se from the input st ... eam, and the test fails. removed lJ�pef' in spt"iciFied c'Htver·sion is enabled, the te.st � ite ... al MUST ' be .:a.se to match the ' input stNtam.
Ue'ince
,r'I �J
;
chr
stream.
4.4.
tJ
��
Any leading blanks are ski�ped. If the next character is the specified From removed is character, then the test passes, and that char�cter the input stream. If it is not the specified character, then t"'e t�st input the from fails. and only the leading blanks have been removed
, ��:,�S;T �
J
=
Character'Test
;�t�:.�,� �.v;, .,i;'��%,!i: ' " .�
-f
,
:
.',.
-" �·.r-
;:
Any t�rm that
starts �ith
p.riod and
a
is
,'r,l .:onsid<:!r·ed a call to · called with a BL instruction and returns . \
flI I
[1
ASMTEST
=
(identifier)
'.
__
ARG
)
.d'
I,t.-I j
)]
n
)]
=
are
[Ca r,>
J
defined by:
(identifier)
(strin9
li teral�
,:,;.,!.:. .•
,:.po . . . "t puaon.te<. pu •• d to the oouti n. by fll ine data st"itements f.:d l.)win, the BL instructioHI.
an e:x:ample, the f.:.ll')UJin9 call:
As
bl data d.:..t.:.. dat"i
ArId
th� t � r·Il'.
•
bl t�xt byte
test
•• iteoating ..;�..<.::.<.,:".,.
_,
will
.ASMEXAMPL( 1234.alpha,"'c)
(
H.e",
gerler'at,,�
as
the
ASME)(AMPL
1234
alpha nc" ASMSTO( IIstr'in,
even '.. "�
of
ASMSTO .' str i n9 of 0
,,.. ..
�.
text")
wi 11
generate:
,-
text ...
/
i
i�
with th� EQ flag set to indicatli' FAIL, and with the EQ flag cl;aoar'ed to indicatli' PASS. RIi'9isters r6 and r7 are USli'd for scanning charact�r5 and must not be and re9ister riO i s a local use stack that may be used but changed. must be restored ·upon re turn. See the source code for the METALIB routines for examples.
1� 1 The optional arguments
i
follow�d by �n id�ntifi�r
I
I
)
tit 4. o. .Inver-t Pass/Fai 1 -j- If any t�st term is
preceeded by a minus sisn, then it/s P&s5/fail status is reversed. For �xampl�. -�" mean s to t�st for a �uot. charact�r, and remoye it if present. Fail if It was pres�nt. and pass .)ther'wise.
4.7.
'1
II
Discard
DTOt<
The
=
....
u,
T�kens
( .
••
1
I�
LJ []
identifili'r'
'i.
Nes ted
that
An...�place choices. 4.10.
, .. : TESTS' ';:
Syntax
I] . . !j
,.
•
and
1 eve 1 s
.
of CHOICES
of
tft .. t,
YOU mav
IJse
a
TESTS,
t�st % (string literal) % t.st with d.limiter check % X inve�t p�ss/fai'- of n�xt t.rm % t�st� . .' ( ( ar, j % as1embl ..., ;ans'JaSt� test ;� % s in91e charact�r test! chI" '( chQices '1 % outer 1.v�1 choices �s a t2rffi � .
:
l
stack
that
'YOU may use a.n ind ividual by enclosing them in (braces).
I l
l�
token
.�oes not have .� period bef.)r'e �t is.� call to ThlS l .... i:s ·.'OIJ d"'". .l',r." Ple.:\!'s . and .:onnect them. The pass/fai 1 status of that prod'Jctiof.L.. b",'::: c.mes the . " , , (arg) pass/fail status of th. term. An example of this is t�; �5e of the that Not� test. language assembly an of specification e th in compatibility for allowed are they as optional, are and) characters ( with&NF rlotation onlv. Usual1'1', they ar'i' not u sed.
Ar�
4.
J .;,
;
:3.
. I . �-rIi;t.tl er .pr":O.jU ':tll)r
,
")
number of tokens are removed from the
indicated
dis.:ar'ded.
4"
1 iterat>
�? �.,-" " "
set · of
.
"
'!-a5�.
---�:.
�ETA
: I-A�TIUN
�1 ;,
i \
1,-
I:'_-J
the ability to repeat a selected term and down the value stored in a .DECLARE vari able. When the �alue IS the repeating ends. The format is: =
U."
actic.n
Me,sage
:
te st)
;
count :�ro.
identifier>
OeOH .. tin. THm •
ERROR
literal>
literal,>
cons.:"
b· ... II seper"ated choices of 1 ist a or ter"m a making isnored. the �e�luting pass/fail st.tus ,is that this dCles rl.)t mean that a mlJl tipl. Rresence , optiorlal. Note, ,choice that passes it's fir�t�erm can fail following terms. By
enclosing
GbracketsJ.
t:)
C" ' ....
D
r: •..J
"$
ter'!TI
P"'l55o.
•
is r-epeated >Jnt il
CALL
TRACE . NOTRACE
it faUst
and the
f�il"''"''status
and
eo
se�luerlC:�1.
opt i.:.na1 : CHOICES
r: ? .�. oJ.
lla u
(
Bot h----o-f ,these terms d isplay the str"ins 1 it.eral' as a listing message. Error will also ,enerate a syntax err·.)r"
U J
?"REPEAT"
.TEXT
•
[�rl",e [l
terms that alwa�s pass, and thus ar0 not some �esi��d action. They are used to �enerate ,meSf.,il.geS, provide optic.nal c'Hlstr'ucts, and r-epEoat
those
perform
Thi� term provides
RF :
. 1-
They
c.)de , outPlJt make parts of the syntax.
��':"
,I
are
Terms
tested.
RPT
1-] ,'
ACT ION Terms
�
ir. it�5 t-a-r'!rI ..
i!: !
T�ace Control
•
These
terms t��n a tr�ca listins of ��ch production as off. This is �s�d t� debu. Y00r META pr09ram. sh.;ould not b
on
and
it
is
Th';'5e
ca11e..:.d, t<:-r'lll_=-
ie6.
OlJtput Cod� Generation
�AS
th� syntax. analY�is of the source code pr09r8558 •• appropriat� ass�mblv language code should b e generated to pe�form the 5tatem�nts. Code mav b� sent .�ir�ctly to the Oytpy t stream (usually the TEMP1$ file) or it may be stored in memory (deferred) for later Oytput. This is usefyl when th� source svntax is in a different order th�n the code that mus t b� generated. An �xampl. of this is a statement t o write data to a di sk f*'e:
I.l �l
I
PR INT
#l;A .• B.C
The l ine to the diSk fil e will be generatad by a write to code program as sembly the analyzing "PRINT #1;" but should not appear in ar,.a.lyzlns bv edite·d been h.a.s printed be to line the afterIJntil is "PRINT #1;" defer'r:e.j "A.B.C". It. this case. the .jutput from thtil IJO til after the OIJtpu t Fr')m "A. S.C" has been generated
•
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3.:2 offer-s 4 seperate deferred OlJtPIJt s tre-:l.rfls. -Hllj ..s. i �.) ver's i'o:on META m.n-str-ea.1T1 b
j /I:.J _
def�,..r-ed a to sent tn that st,..eaffl · to th", of ev.nts sequence
,Generate code fo,.. "PRINT #1;" to a deferre d output stream C;e ner-ate code for- "A. B,e" to thfr dir�.ct output str-eam T,..ansfer all code iri the def err�d �treamto the direct stream.
deferred .,IJtPIJt stream empties it. asainfo'-': new defer-red output codfr.
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that hasbe-erl saved code the In the above example.
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n ume r i c l i te ra l m u s t be e i t h e r 0 f o r def�rred
code
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T h e a c t u a. l c o d e _ t o be senerated is � pe c i f i e d by l i tera l . Th i s is a text , t r i n9 enc l osed in c h a r a c t . r . h a v e f P e c i a, l me a n i n9 s i n s u c h a s t r i n g .
a. s t r i n 9�( c o de » � u o t e s » . Se v e r a l
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7. 2.
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F I LETYPES '
r: 5 e t Y p o p t i o n t h a t mu s t b e p r e 5 n t i rl a ma i n mO. d.U l i: ,:, f. l "" t tHl.t ha s SYNT A X i n it ) i s t h e f il e t Y P ft o p t i o n '. T h i s , ,,!;iJ�.e .: i f i . s ., s e d . f o r s o u r- c e a n d d £o s t i na tY6n f i l e s i f , i hi' t y pe s t o be u d e f a lJ l ·t 'f n ame s 9 i ve n d o n o t h � v e p e r i o d s i n t he m . I t "' s - f 'H' ma t i s :
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