---

11.90 Sample ‘parser’ ¶

Basic MGL script.

MGL code:

title 'MGL parser sample'
# call function
call 'sample'

# ordinary for-loop
for $0 -1 1 0.1
if $0<0:line 0 0 1 $0 'r':else:line 0 0 1 $0 'g':endif
next

# if-elseif-else
for $i -1 1 0.5
if $i<0
text 1.1 $i '$i' 'b'
elseif $i>0
text 1.1 $i '$i' 'r'
else
text 1.1 $i '$i'
endif
next

# ordinary do-while
do
defnum $i $i-0.2
line 0 0 $i 1 'b'
while $i>0

# do-next-break
do
defnum $i $i-0.2
if $i<-1 then break
line 0 0 $i 1 'm'
next

# for-while-continue
for $i -5 10
text $i/5 1.1 'a'+($i+5)
if $i<0
text $i/5-0.06 1.1 '--' 'b'
elseif mod($i,2)=0
text $i/5-0.06 1.1 '~' 'r'
else
# NOTE: 'continue' bypass the 'while'!
continue
endif
# NOTE: 'while' limit the actual number of iterations
while $i<5

# nested loops
for $i 0 1 0.1
for $j 0 1 0.1
ball $i $j
if $j>0.5 then continue
ball $i $j 'b+'
next
next

func 'sample'
new dat 100 'sin(2*pi*(i/99+1))'
plot dat;xrange -1 0
box:axis
xlabel 'x':ylabel 'y'
return

C++ code:

void smgl_parser(mglGraph *gr)	// example of MGL parsing
{	// NOTE: MGL version show much more variants of loops and conditions.
	gr->Title("MGL parser sample");
	double a[100];   // let a_i = sin(4*pi*x), x=0...1
	for(int i=0;i<100;i++)a[i]=sin(2*M_PI*i/99);
	mglParse *parser = new mglParse;
	// Add MGL variable and set yours data to it.
	mglData *d = dynamic_cast<mglData*>(parser->AddVar("dat"));
	if(d)	d->Set(a,100);
	parser->Execute(gr, "plot dat; xrange -1 0\nbox\naxis");
	// You may break script at any line do something
	// and continue after that.
	parser->Execute(gr, "xlabel 'x'\nylabel 'y'\nbox");
	// Also you may use cycles or conditions in script.
	parser->Execute(gr, "for $0 -1 1 0.1\nif $0<0\n"
		"line 0 0 1 $0 'r':else:line 0 0 1 $0 'g'\n"
		"endif\nnext");
	// You may use for or do-while loops as C/C++ one
	double i=1;
	do	{
		char buf[64];	sprintf(buf,"line 0 0 %g 1 'b'",i);
		parser->Execute(gr, buf);	i=i-0.2;
	} while(i>0);
	// or as MGL one.
	parser->Execute(gr, "for $i -1 1 0.5\n"
		"if $i<0\ntext 1.1 $i '$i' 'b'\n"
		"elseif $i>0\ntext 1.1 $i '$i' 'r'\n"
		"else\ntext 1.1 $i '$i'\nendif\nnext\n");
	// There are 'break' and 'continue' commands in MGL too.
	// NOTE: 'next' act as "while(1)" in do-while loops.
	parser->Execute(gr, "do\ndefnum $i $i-0.2\n"
		"if $i<-1 then break\nline 0 0 $i 1 'm'\nnext\n");
	// One issue with 'continue' -- it bypass 'while' checking
	parser->Execute(gr, "for $i -5 10\ntext $i/5 1.1 'a'+($i+5)\nif $i<0\n"
		"text $i/5-0.06 1.1 '--' 'b'\n"
		"elseif mod($i,2)=0\ntext $i/5-0.06 1.1 '~' 'r'\n"
		"else\ncontinue\nendif\n"
		// NOTE: 'while' limit the actual number of iterations in for-loop.
		"while $i<5\n");
	// Finally, MGL support nested loops too.
	parser->Execute(gr, "for $i 0 1 0.1\nfor $j 0 1 0.1\nball $i $j\n"
		"if $j>0.5 then continue\nball $i $j 'b+'\nnext\nnext\n");
	// Clean up memory.
	delete parser;
}