[mkgmap-dev] if-then-else in style and style options

Thu Mar 16 08:34:34 GMT 2017

Hi Andrzej,

well, my problem is the possible misinterpretation caused by ambiguity caused by the if-then interpretation,
but I think I have found a possible solution.

Let's look at some rules for boundaries in the default style:
v1)
boundary=administrative { name '${mkgmap:boundary_name}' }
boundary=administrative & admin_level<3 [0x1e resolution 12]
boundary=administrative & admin_level<5 [0x1d resolution 19]
boundary=administrative & admin_level<7 [0x1c resolution 21]
boundary=administrative & admin_level<9 [0x1c resolution 22]
boundary=administrative [0x1c resolution 22]

We said we want to be able to use if-then like this:
v2)
if (boundary=administrative ) then
{ name '${mkgmap:boundary_name}' }
admin_level<3 [0x1e resolution 12]
admin_level<5 [0x1d resolution 19]
admin_level<7 [0x1c resolution 21]
admin_level<9 [0x1c resolution 22]
[0x1c resolution 22]
end

With r3838 this did not work, because the each rule needs an expression.
Ticker suggested to add a dummy expression like 1=1 so we would write
v3)
if (boundary=administrative ) then
1=1 { name '${mkgmap:boundary_name}' }
admin_level<3 [0x1e resolution 12]
admin_level<5 [0x1d resolution 19]
admin_level<7 [0x1c resolution 21]
admin_level<9 [0x1c resolution 22]
1=1 [0x1c resolution 22]
end

but this is also not working as 1=1 is interpreted as $1='1' instead of "true"

Now I noticed that the scanner allows to use () as an empty expression.
So instead of v1 one already can write
v4)
if (boundary=administrative ) then
() { name '${mkgmap:boundary_name}' }
admin_level<3 [0x1e resolution 12]
admin_level<5 [0x1d resolution 19]
admin_level<7 [0x1c resolution 21]
admin_level<9 [0x1c resolution 22]
() [0x1c resolution 22]
end

If we document this we no longer have a problem with the "one expression two objects" syntax like this:
a=b [0xc ... resolution 24][0x10801 resolution 24]
because we still say that a rule must start with an expression and mkgmap can automaticalyl
add "continue" or "continue with_actions" for all but the last type defintion.

If you don't like the () 'trick' I can again try to make a style function like true()  work.

Gerd
________________________________________
Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von Andrzej Popowski <popej at poczta.onet.pl>
Gesendet: Freitag, 10. März 2017 20:14:49
An: mkgmap-dev at lists.mkgmap.org.uk
Betreff: Re: [mkgmap-dev] if-then-else in style and style options

Hi Gerd,

my idea was more simple, than your implementation. I just would like to
create multiple map objects with single rule. I didn't put "continue"
there, because I assumed, that all element type definition should be
processed.

Still "continue" could be applied, it would mean, that OSM object is
processed further, possibly resulting in 3-rd map object or more. I
think "continue" or "continue with_actions" could be added to last type
definition.

Any other more complicated rules, like adding actions after first type
definition, could be written just like now, with multiple statements.
While I appreciate more flexibility I'm afraid, it could clutter the style.

--
Best regards,
Andrzej
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