Parsing/RPN to infix conversion: Difference between revisions

<br>The same reasoning was used for the ''operator associations'' &nbsp; (the left &nbsp; ◄ &nbsp; and right &nbsp; ► &nbsp; arrow symbols).

<lang rexx>/*REXX program converts Reverse Polish Notation (RPN) ──► ───► an infix notation. */

showAction = 1 # = 0 /*initialize stack pointer0 to 0if no showActions wanted. */

oS # = '+0 - / * ^' /*operator symbols. /*initialize stack pointer to 0 (zero).*/

oPoS = '2+ 2- 3/ 3* 4^' /*the operator prioritiessymbols. */

oAoP = '◄2 ◄2 ◄3 ◄3 ►4' /*the operator associationspriorities. */

say "infix: " toInfix( "1 2 + 3 4 + ^ 5 6 + ^" ) /* [↓] Sprechen Sie Deutsch.? */

exit 0 /*stick a fork in it, we're all done. */

pop: pop= #; #= # - 1; return @.pop

push: #= # + 1; @.#= arg(1); return

stack2str: $=; do j=1 for #; _ = @.j; y= left(_, 1)

if pos(' ', _)==0 then _ = '{'strip( substr(_, 2) )"}"

else _ = substr(_, 2)

$=$ '{'strip(y _)"}"

end /*j*/

return space($)

toInfix: parse arg rpn; say copies('─', 80 - 1); say 'RPN: ' space(rpn)

do N=1 for words(RPN); ?=word(RPN,N) /*process each of the RPN tokens.*/

if pos( ?= word(RPN,oS N)==0 then call push '¥' ? /*whenobtain innext doubt,item addin athe Yenlist. to it.*/

if pos(?,oS)==0 then elsecall do;push '¥' ? g=pop(); /*when in gp=left(gdoubt, 1);add a Yen to g=substr(g, 2)it.*/

h else do; g= pop(); hpgp= left(hg, 1); hg= substr(hg, 2)

tp h=substr pop(oP,pos); hp= left(?h, oS1),; 1 h= substr(h, 2)

ta tp= substr(oAoP, pos(?, oS), 1)

if hp<tp | (hp==tp & ta=='►') then h ta=" substr("h"oA, pos(?, oS), 1)"

if gphp<tp | (gphp==tp & ta=='◄►') then gh= "("gh")"

call push if gp<tp || h(gp==tp & ?ta=='◄') then g= "("g")"

end call push tp || h ? g

if showAction then say right(?,25) "──►" stack2str() end

end /*N*/

return space( substr( pop(), 2) )</lang>

'''{{out|output'''|text=&nbsp; when using the default inputinputs: &nbsp; &nbsp; &nbsp; [Output is very similar to AWK's output.]}}

^ ──► {4 ( Mond * ( Sterne + Schlamm)) ^ ( Feur * Suppe)}