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module reval; % Functions for algebraic evaluation of prefix forms. % Author: Anthony C. Hearn. % Copyright (c) 1991 RAND. All rights reserved. fluid '(!*exp !*intstr !*listargs !*resimp alglist!* dmode!* subfg!* varstack!*); switch listargs; global '(!*resubs !*sqvar!* !*val); symbolic procedure reval u; reval1(u,t); symbolic procedure aeval u; reval1(u,nil); symbolic procedure aeval!* u; % This version rebinds alglist!* to avoid invalid computation in % loops. begin scalar alglist!*; return reval1(u,nil) end; symbolic procedure reval1(u,v); (begin scalar x,y; if null u then return nil % this may give trouble else if stringp u then return u else if fixp u then return if flagp(dmode!*,'convert) then reval2(u,v) else u else if atom u then if null subfg!* then return u else if idp u and (x := get(u,'avalue)) then if u memq varstack!* then recursiveerror u else <<varstack!* := u . varstack!*; return if y := get(car x,'evfn) then apply2(y,u,v) else reval1(cadr x,v)>> else nil else if not idp car u % or car u eq '!*comma!* then errpri2(u,t) else if car u eq '!*sq then return if caddr u and null !*resimp then if null v then u else prepsqxx cadr u else reval2(u,v) else if flagp(car u,'remember) then return rmmbreval(u,v) else if flagp(car u,'opfn) then return reval1(opfneval u,v) else if x := get(car u,'psopfn) then <<u := apply1(x,cdr u); if x := get(x,'cleanupfn) then u := apply2(x,u,v); return u>> % Note that we assume that the results of such functions are % always returned in evaluated form. else if arrayp car u then return reval1(getelv u,v); return if x := getrtype u then if y := get(x,'evfn) then apply2(y,u,v) else rerror(alg,101, list("Missing evaluation for type",x)) else if not atom u and not atom cdr u and null cddr u % Don't pass opr to list if % there is more than one arg. and (y := getrtype cadr u) eq 'list % Only lists and (x := get(y,'aggregatefn)) % for now. and not flagp(car u,'boolean) and not !*listargs and not flagp(car u,'listargp) then apply2(x,u,v) else reval2(u,v) end) where varstack!* := varstack!*; flagop listargp; symbolic procedure rmmbreval(u,v); % The leading operator of u is flagged 'remember. begin scalar fn,x,w,u1,u2; fn := car u; u1:={fn}; u2:={fn}; for each y in cdr u do <<w:=reval1(y,nil); u2:=aconc(u2,w); if eqcar(w,'!*sq) then w:=!*q2a(cadr w); u1:=aconc(u1,w)>>; if (x:=assoc(u1,w:=get(fn,'kvalue))) then<<x:=cadr x; go to a>>; % Evaluate "algebraic procedure" and "algebraic operator" directly. if flagp(fn,'opfn) then x:= reval1(opfneval u2,v) else if get(fn,'simpfn) then x:=!*q2a1(simp!* u2,v) else % All others are passed to reval. << remflag({fn},'remember); x:=reval1(u2,v); flag({fn},'remember); >>; if not smember(u1,x) and not smember(u2,x) then put!-kvalue(fn,get(fn,'kvalue),(car u) . foreach uuu in cdr u collect reval uuu,x); a: return x; end; symbolic procedure remember u; % Remember declaration for operator and procedure names. for each fn in u do <<if not flagp(fn,'opfn) and null get(fn,'simpfn) then <<redmsg(fn,"operator"); mkop fn>>; if flagp(fn,'noval) or flagp(fn,'listargp) then typerr(fn,"remember operator"); flag({fn},'remember); >>; put('remember,'stat,'rlis); symbolic procedure recursiveerror u; msgpri(nil,u,"improperly defined in terms of itself",nil,t); put('quote,'psopfn,'car); % Since we don't want this evaluated. symbolic procedure opfneval u; if flagp(car u ,'remember) then begin scalar interm,resul,x; interm := for each j in (if flagp(car u,'noval) then cdr u else revlis cdr u) collect if fixp j then j else mkquote j; if (x:=assoc(car u . interm ,get(car u,'kvalue))) then return cadr x; resul := lispeval(car u . interm); put!-kvalue(car u,get(car u,'kvalue), car u . interm, resul); return resul; end else lispeval(car u . for each j in (if flagp(car u,'noval) then cdr u else revlis cdr u) collect mkquote j); flag('(reval),'opfn); % to make it a symbolic operator. symbolic procedure reval2(u,v); !*q2a1(simp!* u,v); symbolic procedure getrtype u; % Returns overall algebraic type of u (or NIL is expression is a % scalar). Analysis is incomplete for efficiency reasons. % Type conflicts will later be resolved when expression is evaluated. begin scalar x,y; return if null u then nil % Suggested by P.K.H. Gragert to avoid the % loop caused if NIL has a share flag. else if atom u then if not idp u then not numberp u and getrtype1 u else if flagp(u,'share) % then getrtype lispeval u then if (x := eval u) eq u then nil else getrtype x else if (x := get(u,'avalue)) and not(car x memq '(scalar generic)) or (x := get(u,'rtype)) and (x := list x) then if y := get(car x,'rtypefn) then apply1(y,nil) else car x else nil else if not idp car u then nil else if (x := get(car u,'avalue)) and (x := get(car x,'rtypefn)) then apply1(x,cdr u) else getrtype2 u end; symbolic procedure getrtype1 u; % Placeholder for packages that use vectors. nil; symbolic procedure getrtype2 u; % Placeholder for packages that key expression type to the operator. begin scalar x; % Next line is maybe only needed by EXCALC. return if (x := get(car u,'rtype)) and (x := get(x,'rtypefn)) then apply1(x,cdr u) else if x := get(car u,'rtypefn) then apply1(x,cdr u) else nil end; remprop('rtypecar,'stat); symbolic procedure rtypecar u; for each j in u do put(j,'rtypefn,'getrtypecar); deflist('((rtypecar rlis)),'stat); rtypecar difference,expt,minus,plus,recip; deflist(' ((quotient getrtypeor) (times getrtypeor) (!*sq (lambda (x) nil)) ),'rtypefn); symbolic procedure getrtypecar u; getrtype car u; symbolic procedure getrtypeor u; u and (getrtype car u or getrtypeor cdr u); symbolic procedure !*eqn2a u; % If u is an equation a=b, it is converted to an equivalent equation % a-b=0, or if a=0, b=0. Otherwise u is returned converted to true % prefix form. if not eqexpr u then prepsqyy u else if null cdr u or null cddr u or cdddr u then typerr(u,"equation") else (if rh=0 then lh else if lh=0 then rh else{'difference,lh,rh}) where lh=prepsqyy cadr u,rh=prepsqyy caddr u; symbolic procedure prepsqyy u; if eqcar(u,'!*sq) then prepsqxx cadr u else u; symbolic procedure getelv u; % Returns the value of the array element U. % getel(car u . for each x in cdr u collect ieval x); getel(car u . for each x in cdr u collect reval_without_mod x); symbolic procedure setelv(u,v); % setel(car u . for each x in cdr u collect ieval x,v); setel(car u . for each x in cdr u collect reval_without_mod x,v); symbolic procedure reval_without_mod u; % Evaluate u without a modulus. if dmode!* eq '!:mod!: then (reval u where dmode!* = nil) else reval u; symbolic procedure revlis u; for each j in u collect reval j; symbolic procedure revop1 u; if !*val then car u . revlis cdr u else u; symbolic procedure mk!*sq u; % Modified by Francis J. Wright to return a list correctly. % if null numr u then 0 % else if atom numr u and denr u=1 then numr u % else '!*sq . expchk u . if !*resubs then !*sqvar!* else list nil; (if null numr u then 0 else if atom numr u and denr u=1 then numr u else if kernp u and eqcar(mvar numr u,'list) then mvar numr u else '!*sq . u . if !*resubs then !*sqvar!* else list nil) where u=expchk u; symbolic macro procedure !*sq u; % Provide an interface to symbolic mode. prepsq cadr u; symbolic procedure expchk u; if !*exp then u else offexpchk u; symbolic procedure lengthreval u; begin scalar v,w,x; if length u neq 1 then rerror(alg,11, "LENGTH called with wrong number of arguments"); u := car u; if idp u and arrayp u then return 'list . get(u,'dimension); v := aeval u; if (w := getrtype v) and (x := get(w,'lengthfn)) then return apply1(x,v) else if atom v then return 1 else if not idp car v or not(x := get(car v,'lengthfn)) then if w then lprie list("LENGTH not defined for argument of type",w) else typerr(u,"LENGTH argument") else return apply1(x,cdr v) end; put('length,'psopfn,'lengthreval); % Code for evaluation of expressions whose type can only be % infered after partial evaluation. symbolic procedure yetunknowntypeeval(u,v); % Assumes that only psopfn's can produce yet unknown types. reval1(eval!-yetunknowntypeexpr(u,v),v); symbolic procedure eval!-yetunknowntypeexpr(u,v); if atom u then ((if w then eval!-yetunknowntypeexpr(cadr w,v) else u) where w = get(u,'avalue)) else if car u eq '!*sq or get(car u,'dname) or car u eq '!:dn!: then u else ((if x and (getrtype u eq 'yetunknowntype) then apply1(x,cdr u) else car u . for each j in cdr u collect eval!-yetunknowntypeexpr(j,v)) where x = get(car u,'psopfn)); put('yetunknowntype,'evfn,'yetunknowntypeeval); endmodule; end;