Re: [NTG-context] ! Declared variable conflicts with previous vardef [Metapost]

Hi,

On 3 Jan 2019, at 11:31, Fabrice Couvreur wrote:

Hi, It is true that Alan has already answered this question but I was misled because the file that I compiled without problem is this one, even leaving pair z[ ] (I can think that it is because of this instruction z := point 3.6 of p ;)

It works because of the "pair z” statement. Attempted explanation: Metapost variable names are built up hierarchically. When you say “path p” or “color V.Q” or “numeric z[]” or “vardef z”, it changes the type of just the last segment, not other segments (not even the immediately preceding one). Note that in the case of z[], the last variable segment is the common subscript [] not the ‘alphabetical segment’ “z”. It is actually OK to say e,g, pair z ; color z[]; numeric z[].a; z := point 3.6 of p ; z[1] := red; path z[]; % z[1] is now undefined again after this line, % but z[].a is still numeric z[3] = unitsquare; z[2].a = 5; Redeclaration of intermediate segments works for all declarations except for ‘vardef’. The reason behind this is that vardefs can have suffixes, and metapost does not really differentiate between vardefs defined with and without suffixes (except when called). Of course actual suffixes would interfere with the parsing of any potentially following name segments, which is why re-declarations ‘below’ a vardef’d segment are illegal. I hope that makes sense, it is not the easiest thing to explain. Best wishes, Taco

\starttext \startMPpage[offset=2pt] path p, q, r, b ; pair z ; p := unitsquare scaled 4cm ; z := point 3.6 of p ; q := z--urcorner p ; r := z--urcorner p-- reverse bottomboundary p--cycle ; b := reverse bottomboundary p ; %r := q -- reverse bottomboundary p -- cycle ; definition of Hans draw b--q withpen pencircle scaled 1mm withcolor red ; draw p ; draw r numberstriped (.25,10,5) withcolor magenta ; label.llft("B", p) ; label.lrt("C", p) ; label.ulft("A", p) ; label.urt("D", p) ; label.lft("M", p) ; \stopMPpage \startMPpage[offset=2pt] defaultfont := "texgyrepagella-regular*default" ; defaultscale :=0.8 ; path p, q, r, b ; pair z[]; p := unitsquare xyscaled (9cm,5cm) ; z[0] = (2cm,0cm) ; z[1] = (2cm,2cm) ; z[2] = (0cm,2cm) ; q := llcorner p--z[0]--z[1]--z[2]--cycle ; r := unitsquare xyscaled (7cm,3cm) shifted(2cm,2cm) ; b := z[2]--z[1]--ulcorner r--urcorner p--lrcorner r--z[1]--z[0]--llcorner p--cycle ; draw p ; draw b numberstriped (.25,15,5) withcolor magenta ; label.llft("A", p) ; label.lrt("D", p) ; label.ulft("C", p) ; label.urt("B", p) ; label.lft("M", z[2]) ; label.ulft("N", z[1]) ; label.bot("P", z[0]) ; label.top("J", ulcorner r) ; label.rt("I", lrcorner r) ; label.bot(btex $x$ etex,(llcorner p+z[0])/2); label.lft(btex $x$ etex,(llcorner p+z[2])/2); \stopMPpage

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Le jeu. 3 janv. 2019 à 07:12, Alan Braslau a écrit : On Thu, 3 Jan 2019 16:22:06 +1300 (UTC) Henri Menke wrote:

...

z is a MetaPost intrinsic, something along the lines of

vardef z@#=(x@#,y@#) enddef;

so you can't use the same name for a pair. Actually you can simply delete the declaration

pair z[];

I had already told Fabrice this a couple of days ago...

Alan ___________________________________________________________________________________ If your question is of interest to others as well, please add an entry to the Wiki!

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Taco Hoekwater Elvenkind BV