New features in macro system to support defining python-like syntax

Label: ♦english ♦news

[224] New features in macro system to support defining python-like syntax

fu created at Sunday, 2010-04-25, 05:40:10

fu modified at Sunday, 2010-04-25, 05:51:59

0 Replies, 1740 Hits

A new feature has just been added to the Dao macro system, this new feature allows defining python style indentation sensitive syntax. It is pretty simple to do this now, an example with explanation is available in the svn on google code: demo/macro/scoping_by_indentation.dao

The key point is to use $IBL prefixed macro variable instead of $BL prefixed variable, to match Indented code BLock, which means the matching is stopped once a line with indentation narrower than the indentation of the first matched line.

Another key point is to use indentation alignment @X marker to force all tokens followed by the same marker to have the same indentation. This is need to properly handle if-elif-else constructs.

Just for convenience, that scoping_by_indentation.dao is listed here,

#{
Indentation mark:
@x: where x=1,2,...,9,
tokens followed with the same indentation mark
must be aligned with the same indentation;

Indented code block:
$IBL prefixed variable matches a block of indented codes;

String literal from tokens:
Tokens expanded for patterns between a pair of \" or \',
are concatenated into a string literal enclosed in the
corresponding quotation mark. A space is inserted between
to consecutive identifer tokens.
#}

syntax{ # if : elif : else :
if @1 $EXP_1 : \[ $IBL_1 \]
\{ elif @1 $EXP_2 : \[ $IBL_2 \] \}
\[ else @1 : \[ $IBL_3 \] \]

}as{ # if(){}elif(){}else{}
if( 1 ){ # extra nesting to avoid the inside messing up with the outside
if( $EXP_1 ){ \[ $IBL_1 \] }
\{ elif( $EXP_2 ){ \[ $IBL_2 \] } \}
\[ else{ \[ $IBL_3 \] } \]
}
}

a = 1
b = 0

if a == 0 :
io.writeln( 'python "if" works!' )
if b == 1 :
io.writeln( 'b =', b )
elif a == 1 :
io.writeln( 'python "if-elif" works!' )
if b == 0 :
io.writeln( 'b =', b )

list1 = { 1, 2, 3 }
list2 = { 'a', 'b', 'c' }

for x in list1:
io.writeln( x )
for y in list2:
io.writeln( y )
if y == 'b':
io.writeln( y )

for x in list1 , y in list2 :
io.writeln( x, y )

Compiling options can be set in Dao source codes by changing member values of the global object daoConfig : daoConfig.tabspace is the number of spaces counted for a tab; daoConfig.chindent indicates if indentation should be checked. When the indentation is check, the proper indentation width is chosen as the most frequent indentation width in the source codes, and a warning is printed if the indentation width of a line is not a multiplication of the chosen indentation width.

A few additional features are also implemented to enhance the macro. One is to allow creating string literals from tokens: tokens expanded for patterns between a pair of \" or \' , are concatenated into a string literal, enclosed in the corresponding quotation mark. A space is inserted between to consecutive identifer tokens.

The other is to allow multiple uses of a source pattern in target syntax. This makes macro more flexible and more expressive.

For example:

syntax{
var $ID_1 = $ID_2 = $EXP_1
}as{
var $ID_1 = $EXP_1; var $ID_2 = $ID_1
io.writeln( \" $ID_1 and $ID_2 are defined as the result of $EXP_1 \" );
}
var a = b = math.sqrt( 2 );
io.writeln( a, b );

Executing this code will print out:

a and b are defined as the result of math.sqrt(2)
1.414214 1.414214

Source URL: http://www.daovm.net/space/dao/thread/224

Comments

Change picture: