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from typing import Dict, Set
from pegen.first_sets import FirstSetCalculator
from pegen.grammar import Grammar
from pegen.grammar_parser import GeneratedParser as GrammarParser
from pegen.utils import parse_string
def calculate_first_sets(grammar_source: str) -> Dict[str, Set[str]]:
grammar: Grammar = parse_string(grammar_source, GrammarParser)
return FirstSetCalculator(grammar.rules).calculate()
def test_alternatives() -> None:
grammar = """
start: expr NEWLINE? ENDMARKER
expr: A | B
A: 'a' | '-'
B: 'b' | '+'
"""
assert calculate_first_sets(grammar) == {
"A": {"'a'", "'-'"},
"B": {"'+'", "'b'"},
"expr": {"'+'", "'a'", "'b'", "'-'"},
"start": {"'+'", "'a'", "'b'", "'-'"},
}
def test_optionals() -> None:
grammar = """
start: expr NEWLINE
expr: ['a'] ['b'] 'c'
"""
assert calculate_first_sets(grammar) == {
"expr": {"'c'", "'a'", "'b'"},
"start": {"'c'", "'a'", "'b'"},
}
def test_repeat_with_separator() -> None:
grammar = """
start: ','.thing+ NEWLINE
thing: NUMBER
"""
assert calculate_first_sets(grammar) == {"thing": {"NUMBER"}, "start": {"NUMBER"}}
def test_optional_operator() -> None:
grammar = """
start: sum NEWLINE
sum: (term)? 'b'
term: NUMBER
"""
assert calculate_first_sets(grammar) == {
"term": {"NUMBER"},
"sum": {"NUMBER", "'b'"},
"start": {"'b'", "NUMBER"},
}
def test_optional_literal() -> None:
grammar = """
start: sum NEWLINE
sum: '+' ? term
term: NUMBER
"""
assert calculate_first_sets(grammar) == {
"term": {"NUMBER"},
"sum": {"'+'", "NUMBER"},
"start": {"'+'", "NUMBER"},
}
def test_optional_after() -> None:
grammar = """
start: term NEWLINE
term: NUMBER ['+']
"""
assert calculate_first_sets(grammar) == {"term": {"NUMBER"}, "start": {"NUMBER"}}
def test_optional_before() -> None:
grammar = """
start: term NEWLINE
term: ['+'] NUMBER
"""
assert calculate_first_sets(grammar) == {"term": {"NUMBER", "'+'"}, "start": {"NUMBER", "'+'"}}
def test_repeat_0() -> None:
grammar = """
start: thing* "+" NEWLINE
thing: NUMBER
"""
assert calculate_first_sets(grammar) == {"thing": {"NUMBER"}, "start": {'"+"', "NUMBER"}}
def test_repeat_0_with_group() -> None:
grammar = """
start: ('+' '-')* term NEWLINE
term: NUMBER
"""
assert calculate_first_sets(grammar) == {"term": {"NUMBER"}, "start": {"'+'", "NUMBER"}}
def test_repeat_1() -> None:
grammar = """
start: thing+ '-' NEWLINE
thing: NUMBER
"""
assert calculate_first_sets(grammar) == {"thing": {"NUMBER"}, "start": {"NUMBER"}}
def test_repeat_1_with_group() -> None:
grammar = """
start: ('+' term)+ term NEWLINE
term: NUMBER
"""
assert calculate_first_sets(grammar) == {"term": {"NUMBER"}, "start": {"'+'"}}
def test_gather() -> None:
grammar = """
start: ','.thing+ NEWLINE
thing: NUMBER
"""
assert calculate_first_sets(grammar) == {"thing": {"NUMBER"}, "start": {"NUMBER"}}
def test_positive_lookahead() -> None:
grammar = """
start: expr NEWLINE
expr: &'a' opt
opt: 'a' | 'b' | 'c'
"""
assert calculate_first_sets(grammar) == {
"expr": {"'a'"},
"start": {"'a'"},
"opt": {"'b'", "'c'", "'a'"},
}
def test_negative_lookahead() -> None:
grammar = """
start: expr NEWLINE
expr: !'a' opt
opt: 'a' | 'b' | 'c'
"""
assert calculate_first_sets(grammar) == {
"opt": {"'b'", "'a'", "'c'"},
"expr": {"'b'", "'c'"},
"start": {"'b'", "'c'"},
}
def test_left_recursion() -> None:
grammar = """
start: expr NEWLINE
expr: ('-' term | expr '+' term | term)
term: NUMBER
foo: 'foo'
bar: 'bar'
baz: 'baz'
"""
assert calculate_first_sets(grammar) == {
"expr": {"NUMBER", "'-'"},
"term": {"NUMBER"},
"start": {"NUMBER", "'-'"},
"foo": {"'foo'"},
"bar": {"'bar'"},
"baz": {"'baz'"},
}
def test_advance_left_recursion() -> None:
grammar = """
start: NUMBER | sign start
sign: ['-']
"""
assert calculate_first_sets(grammar) == {"sign": {"'-'", ""}, "start": {"'-'", "NUMBER"}}
def test_mutual_left_recursion() -> None:
grammar = """
start: foo 'E'
foo: bar 'A' | 'B'
bar: foo 'C' | 'D'
"""
assert calculate_first_sets(grammar) == {
"foo": {"'D'", "'B'"},
"bar": {"'D'"},
"start": {"'D'", "'B'"},
}
def test_nasty_left_recursion() -> None:
# TODO: Validate this
grammar = """
start: target '='
target: maybe '+' | NAME
maybe: maybe '-' | target
"""
assert calculate_first_sets(grammar) == {"maybe": set(), "target": {"NAME"}, "start": {"NAME"}}
def test_nullable_rule() -> None:
grammar = """
start: sign thing $
sign: ['-']
thing: NUMBER
"""
assert calculate_first_sets(grammar) == {
"sign": {"", "'-'"},
"thing": {"NUMBER"},
"start": {"NUMBER", "'-'"},
}
def test_epsilon_production_in_start_rule() -> None:
grammar = """
start: ['-'] $
"""
assert calculate_first_sets(grammar) == {"start": {"ENDMARKER", "'-'"}}
def test_multiple_nullable_rules() -> None:
grammar = """
start: sign thing other another $
sign: ['-']
thing: ['+']
other: '*'
another: '/'
"""
assert calculate_first_sets(grammar) == {
"sign": {"", "'-'"},
"thing": {"'+'", ""},
"start": {"'+'", "'-'", "'*'"},
"other": {"'*'"},
"another": {"'/'"},
}
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