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"""
The Lox language grammar
From Robert Nystrom's "Crafting Interpreters"
http://craftinginterpreters.com/
The BNF for the Lox language is at http://craftinginterpreters.com/appendix-i.html
"""
import pyparsing as pp
pp.ParserElement.enable_packrat()
# punctuation
COMMA, LPAR, RPAR, LBRACE, RBRACE, EQ, SEMI = map(pp.Suppress, ",(){}=;")
# keywords
(CLASS, FUN, VAR, FOR, IF, ELSE, PRINT, RETURN, WHILE,
TRUE, FALSE, NIL, THIS, SUPER, AND, OR) = pp.Keyword.using_each(
"class fun var for if else print return while"
" true false nil this super and or".split()
)
identifier = pp.Word(pp.alphas + "_", pp.alphanums + "_'")
string = pp.QuotedString('"')
number = pp.Regex(r"\d+(?:\.\d+)?")
declaration = pp.Forward()
statement = pp.Forward()
class_decl = pp.Forward()
expression = pp.Forward()
block = pp.Forward()
arguments = pp.DelimitedList(expression)
parameters = pp.DelimitedList(identifier)
function = identifier + LPAR + pp.Opt(parameters) + RPAR + block
property_ = identifier + block
fun_decl = FUN + function
var_decl = VAR + identifier + pp.Opt(EQ + expression) + SEMI
class_decl <<= (
CLASS
- identifier
+ pp.Opt("<" + identifier)
+ LBRACE
+ (function | property_ | class_decl)[...]
+ RBRACE
)
primary = (TRUE | FALSE | NIL | THIS | number | string | identifier
| SUPER + "." + identifier
# | LPAR + expression + RPAR <-- not needed, infix_notation takes care of this
).set_name("primary")
call = primary + (
LPAR + pp.Opt(arguments) + RPAR
| "." + identifier
)[1, ...]
arith_expression = pp.infix_notation(
(call | primary).set_name("arith_operand"),
[
(pp.one_of("! -"), 1, pp.opAssoc.RIGHT),
(pp.one_of("/ *"), 2, pp.opAssoc.LEFT),
(pp.one_of("- +"), 2, pp.opAssoc.LEFT),
(pp.one_of("> >= < <="), 2, pp.opAssoc.LEFT),
(pp.one_of("!= =="), 2, pp.opAssoc.LEFT),
(AND, 2, pp.opAssoc.LEFT),
(OR, 2, pp.opAssoc.LEFT),
]
)
assignment = pp.Forward()
assignment <<= (call | identifier) + EQ + (assignment | arith_expression)
expression <<= assignment ^ arith_expression ^ function
block <<= pp.Group(LBRACE + declaration[...] + RBRACE)
while_statement = WHILE + LPAR + expression + RPAR + statement
return_statement = RETURN + pp.Opt(expression) + SEMI
print_statement = PRINT + expression + SEMI
if_statement = IF + LPAR + expression + RPAR + statement + pp.Opt(ELSE + statement)
expr_statement = expression + ";"
for_statement = FOR + LPAR + pp.Group(
(var_decl | expr_statement | ";")
+ pp.Opt(expression) + ";"
+ pp.Opt(expression)
) + RPAR + statement
statement <<= pp.Group(
expr_statement
| for_statement
| if_statement
| print_statement
| return_statement
| while_statement
| block
)
declaration <<= (
class_decl
| fun_decl
| var_decl
| statement
)
program = declaration[...]
program.ignore(pp.dbl_slash_comment)
# define names so that we get a better diagram
pp.autoname_elements()
def main():
import textwrap
success, _ = program.run_tests(
textwrap.dedent(t) for t in [
"""\
var a = 1;
{
var a = a + 2;
print a;
}
""",
"""\
{
var i = 0;
while (i < 10) {
print i;
i = i + 1;
}
}
""",
"""\
var a = 0;
var temp;
for (var b = 1; a < 10000; b = temp + b) {
print a;
temp = a;
a = b;
}
""",
"""\
fun add(a, b, c) {
print a + b + c;
}
add(1, 2, 3);
""",
"""\
fun count(n) {
while (n < 100) {
if (n == 3) return n; // <--
print n;
n = n + 1;
}
}
count(1);
""",
"""\
fun fib(n) {
if (n <= 1) return n;
return fib(n - 2) + fib(n - 1);
}
for (var i = 0; i < 20; i = i + 1) {
print fib(i);
}
""",
"""\
fun makeCounter() {
var i = 0;
fun count() {
i = i + 1;
print i;
}
return count;
}
var counter = makeCounter();
counter(); // "1".
counter(); // "2".
""",
"""\
fun thrice(fn) {
for (var i = 1; i <= 3; i = i + 1) {
fn(i);
}
}
thrice(fun (a) {
print a;
});
// "1".
// "2".
// "3".
""",
"""\
class Math {
square(n) {
return n * n;
}
}
print Math.square(3); // Prints "9".
""",
"""\
class Circle {
init(radius) {
this.radius = radius;
}
area {
return 3.141592653 * this.radius * this.radius;
}
}
var circle = Circle(4);
print circle.area; // Prints roughly "50.2655".
""",
"""\
// Your first Lox program!
print "Hello, world!";
"""
]
)
assert success
if __name__ == '__main__':
import contextlib
with contextlib.suppress(Exception):
program.create_diagram("lox_parser_diagram.html", vertical=2, show_groups=True)
main()