DSL ~ LARK Documentation

LARK is the parsing tool used by the domain specific language team to enable algorithmic, grammar based conversion of dsl files, which are largely written in plaintext, to a WDL++.

There are 5 Parts to creating a lark file:

1. Writing the grammar
2. Creating the parser
3. Shaping the tree
4. Evaluating the tree
5. Optimizing

Writing the Grammar

Creating the Parser

Shaping the Tree

Evaluating the Tree

Optimizing

Example calculator built using LARK:

from lark import Lark, Transformer, v_args
 
try:
    input = raw_input
except NameError:
    pass
 
my_grammar_calc = """
    %import common.CNAME -> NAME
    %import common.NUMBER
    %import common.WS_INLINE
    %ignore WS_INLINE
 
    ?start: value -> number
    ?value: add
        | SIGNED_NUMBER -> assign_var
    ?add: sub
        | add "+" sub -> add
    ?sub: mult
        | sub "-" mult -> sub
    ?mult: div
        | mult "*" div -> mul
    ?div: neg
        | div "/" neg -> div
    ?neg: parenth
        | "-" parenth -> neg
    ?parenth: value
        |"(" value ")"
"""
 
@v_args(inline = True)
class my_calc_tree(Transformer):
    from operator import add, sub, mul, truediv as div, neg
    number = float
    def __init__(self):
        self.vars = {}
    def assign_var(self, nm, val):
        self.vars[name] = val
 
parse_my_calc = Lark(my_grammar_calc, parser = 'lalr', transformer=my_calc_tree())
calculator = parse_my_calc.parse
 
def test():
    print(calculator("a = 3+4"));
    print(calculator("a = 3/4"));
    print(calculator("a = 3*4"));
    print(calculator("a = 3-4"));
 
test()