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Conditional directives may be used to conditionnaly skip blocks of
code. There are 4 conditional directives: if, elseif,
else and endif. +if begins a conditional directives
sequence, with argument a conditional expression. If the expression is
true the block of code following the +if is output in the
resulting file, up to another conditional directive, if it is false
the code block is skipped. If the
expression is false and the following conditional directive is
+elseif, the same procedure is followed with the argument of
+elseif
which is also a conditionnal expression. More than one +elseif
may follow a +if. If a +if or +elseif expression
is true the following
code block is output and all
the following +elseif code blocks are skipped. If all the +if
and +elseif expressions are false and
the following coditionnal
directive is +else then the block following the
+else is output. If a previous expression was true the
code block following the +else is skipped. The last code block
is closed by +endif.
Conditionnal directives may be nested, a +if begins a deeper
conditionnal sequences directives that is ended by the corresponding
+endif.
The simplest example is:
some code;
+IF,monitor
code output only if monitor is true;
+ENDIF
If ‘monitor’ is selected, the +if block is output, it leads to
some code;
code output only if monitor is true;
If ‘monitor’ isn’t selected the +if block is skipped, it leads to
some code;
An example with +else may be:
+IF,double call dmysub(eta); +ELSE call smysub(eta); +ENDIF
If ‘double’ is selected the code output is call dmysub(eta);,
if ‘double’ isn’t selected the code output is call dmysub(eta);.
Here is a self explanatory example of use of +elseif:
+IF,monitor code used if monitor is selected; +ELSEIF,kalman code used if kalman is selected and monitor is not; +ELSE code used if kalman and monitor are not selected; +ENDIF
And last an example of nested conditional directives:
+IF,monitor
code used if monitor is selected;
+_IF,kalman. deep if
code used if monitor and kalman are selected;
+_ELSE. deep else
code used if monitor is selected and kalman is not;
+_ENDIF. end the deep conditionnals sequence
+ELSE
code used if monitor is not selected;
+_IF,kalman
code used if monitor is not selected but kalman is;
+_ELSE
code used if monitor and kalman are not selected;
+_ENDIF
other code used if monitor is not selected;
+ENDIF
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