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varsubst.jison
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varsubst.jison
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/* description: Parses end executes mathematical expressions. */
/* lexical grammar */
%lex
symbol [A-Za-z]{1}[A-Za-z0-9_]*
string [^$}]+
%%
"$$" return 'ESCAPE'
"${" return '${'
"$" return '$'
"}" return '}'
":-" return ':-'
"." return '.'
{symbol} return 'SYMBOL'
{string} return 'STRING'
<<EOF>> return 'EOF'
/lex
/* operator associations and precedence */
%left ':-'
%right '$'
%start output
%% /* language grammar */
output
: EOF
{return '';}
| output EOF
{ return $1; }
| output text
{$$ = $1.concat($2);}
| output special_token
{$$ = $1.concat($2);}
| special_token
{$$ = $1;}
| text
{$$ = $1;}
;
text
: string
{$$ = $1;}
| variable
{$$ = $1;}
| SYMBOL
{$$ = $1;}
;
special_token
: '}'
{$$ = $1;}
| ':-'
{$$ = $1;}
;
combined
: combined text
{$$ = $1.concat($2);}
| text
{$$ = $1;}
;
variable
: '${' symbol ':-' combined '}'
{$$ = $2 ? $2.toString() : $4;}
| '${' symbol '}'
{$$ = $2.toString();}
| '$' symbol
{$$ = $2.toString();}
;
symbol
: symbol '.' SYMBOL
{$$ = $1 ? ($1[$3] != null ? $1[$3] : '') : '';}
| SYMBOL
{$$ = yy.context[$1] != null ? yy.context[$1] : '';}
;
string
: ESCAPE
{$$ = '$';}
| STRING
{$$ = $1;}
;