tasks a-s
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Ingy döt Net
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12433 changed files with 156208 additions and 123 deletions
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/* REXX ***************************************************************
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* 09.11.2012 Walter Pachl translates from PL/I
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**********************************************************************/
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fid='rpl.txt'
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ex=linein(fid)
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Say 'Input:' ex
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/* ex=' 3 4 2 * 1 5 - 2 3 ^ ^ / +' */
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Numeric Digits 15
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expr=''
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st.=0
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Say 'Stack contents:'
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do While ex<>''
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Parse Var ex ch +1 ex
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expr=expr||ch;
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if ch<>' ' then do
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select
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When pos(ch,'0123456789')>0 Then Do
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Call stack ch
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Iterate
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End
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when ch='+' Then do; operand=getstack(); st.sti = st.sti + operand; end;
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when ch='-' Then do; operand=getstack(); st.sti = st.sti - operand; end;
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when ch='*' Then do; operand=getstack(); st.sti = st.sti * operand; end;
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when ch='/' Then do; operand=getstack(); st.sti = st.sti / operand; end;
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when ch='^' Then do; operand=getstack(); st.sti = st.sti ** operand; end;
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end;
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call show_stack
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end
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end
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Say 'The reverse polish expression = 'expr
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Say 'The evaluated expression = 'st.1
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Exit
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stack: Procedure Expose st.
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/* put the argument on top of the stack */
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z=st.0+1
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st.z=arg(1)
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st.0=z
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Return
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getstack: Procedure Expose st. sti
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/* remove and return the stack's top element */
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z=st.0
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stk=st.z
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st.0=st.0-1
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sti=st.0
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Return stk
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show_stack: procedure Expose st.
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/* show the stack's contents */
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ol=''
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do i=1 To st.0
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ol=ol format(st.i,5,10)
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End
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Say ol
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Return
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/*REXX program evaluates a Reverse Polish notation (RPN) expression.*/
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parse arg x; if x='' then x = '3 4 2 * 1 5 - 2 3 ^ ^ / +'; ox=x
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showSteps=1 /*set to 0 (zero) if working steps not wanted.*/
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x=space(x); tokens=words(x)
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do i=1 for tokens; @.i=word(x,i); end /*i*/ /*assign input tokens*/
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L=max(20,length(x)) /*use 20 for the min show width. */
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numeric digits L /*ensure enough digits for answer*/
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say center('operand',L,'─') center('stack',L*2,'─'); e='***error!***'
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op='- + / * ^'; add2s='add to───►stack'; z=; stack=
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do #=1 for tokens; ?=@.#; ??=? /*process each token from @. list*/
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w=words(stack) /*stack count (# entries).*/
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if datatype(?,'N') then do; stack=stack ?; call show add2s; iterate; end
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if ?=='^' then ??="**" /*REXXify ^ ──► ** (make legal)*/
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interpret 'y=' word(stack,w-1) ?? word(stack,w) /*compute.*/
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if datatype(y,'W') then y=y/1 /*normalize the number with ÷ */
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_=subword(stack,1,w-2); stack=_ y /*rebuild the stack with answer. */
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call show ?
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end /*#*/
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z=space(z stack) /*append any residual entries. */
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say; say ' RPN input:' ox; say ' answer──►' z /*show input & ans.*/
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parse source upper . y . /*invoked via C.L. or REXX pgm?*/
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if y=='COMMAND' | \datatype(z,'W') then exit /*stick a fork in it, done.*/
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else return z /*RESULT ──► invoker.*/
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/*──────────────────────────────────SHOW subroutine─────────────────────*/
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show: if showSteps then say center(arg(1),L) left(space(stack),L); return
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/*REXX program evaluates a Reverse Polish notation (RPN) expression.*/
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parse arg x; if x='' then x = '3 4 2 * 1 5 - 2 3 ^ ^ / +'; ox=x
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showSteps=1 /*set to 0 (zero) if working steps not wanted.*/
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x=space(x); tokens=words(x) /*elide extra blanks;count tokens*/
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do i=1 for tokens; @.i=word(x,i); end /*i*/ /*assign input tokens*/
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L=max(20,length(x)) /*use 20 for the min show width. */
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numeric digits L /*ensure enough digits for answer*/
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say center('operand',L,'─') center('stack',L*2,'─'); e='***error!***'
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add2s='add to───►stack'; z=; stack=
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dop='/ // % ÷'; bop='& | &&' /*division ops; binary operands*/
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aop='- + * ^ **' dop bop; lop=aop '||' /*arithmetic ops; legal operands*/
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do #=1 for tokens; ?=@.#; ??=? /*process each token from @. list*/
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w=words(stack); b=word(stack,max(1,w)) /*stack count; last entry.*/
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a=word(stack,max(1,w-1)) /*stack's "first" operand.*/
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division =wordpos(?,dop)\==0 /*flag: doing a division.*/
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arith =wordpos(?,aop)\==0 /*flag: doing arithmetic.*/
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bitOp =wordpos(?,bop)\==0 /*flag: doing binary math*/
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if datatype(?,'N') then do; stack=stack ?; call show add2s; iterate; end
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if wordpos(?,lop)==0 then do; z=e 'illegal operator:' ?; leave; end
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if w<2 then do; z=e 'illegal RPN expression.'; leave; end
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if ?=='^' then ??="**" /*REXXify ^ ──► ** (make legal)*/
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if ?=='÷' then ??="/" /*REXXify ÷ ──► / (make legal)*/
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if division & b=0 then do; z=e 'division by zero: ' b; leave; end
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if bitOp & \isBit(a) then do; z=e "token isn't logical: " a; leave; end
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if bitOp & \isBit(b) then do; z=e "token isn't logical: " b; leave; end
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interpret 'y=' a ?? b /*compute with two stack operands*/
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if datatype(y,'W') then y=y/1 /*normalize number with ÷ by 1.*/
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_=subword(stack,1,w-2); stack=_ y /*rebuild the stack with answer. */
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call show ?
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end /*#*/
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if word(z,1)==e then stack= /*handle special case of errors. */
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z=space(z stack) /*append any residual entries. */
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say; say ' RPN input:' ox; say ' answer──►' z /*show input & ans.*/
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parse source upper . how . /*invoked via C.L. or REXX pgm?*/
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if how=='COMMAND' | ,
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\datatype(z,'W') then exit /*stick a fork in it, we're done.*/
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return z /*return Z ──► invoker (RESULT).*/
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/*──────────────────────────────────subroutines─────────────────────────*/
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isBit: return arg(1)==0 | arg(1)==1 /*returns 1 if arg1 is bin bit.*/
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show: if showSteps then say center(arg(1),L) left(space(stack),L); return
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