Tracing
Polar tracing shows logs of how a query is evaluated.
Enabling Tracing
Debug mode is enabled by setting an environment variable: POLAR_LOG=1.
It will print out [debug] messages during query evaluation that show how the query is executed.
Notable things include:
-
Queries and sub-query evaluations.
-
Showing values that are bound to variables for each expression.
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Showing which rules a Polar predicate call will evaluate.
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Showing values returned from calls into the application.
Example
query> f(12);
[debug] QUERY: f(12), BINDINGS: {}
[debug] APPLICABLE_RULES: [
[debug] f(x) if new (Foo{x: x}, _instance_2) and .(_instance_2, foo(), _value_1) and _value_1 = x;
[debug] f(x) if x = 1;
[debug] f(x) if x + 1 and _op_3 == 2;
[debug] ]
[debug] RULE:
[debug] f(x) if
[debug] new Foo(x: x).foo() = x
[debug] QUERY: new (Foo{x: _x_10}, _instance_2_11) and .(_instance_2_11, foo(), _value_1_12) and _value_1_12 = _x_10, BINDINGS: {"_x_10": "12"}
[debug] QUERY: new (Foo{x: _x_10}, _instance_2_11), BINDINGS: {"_x_10": "12"}
[debug] QUERY: .(_instance_2_11, foo(), _value_1_12) and _value_1_12 = _x_10, BINDINGS: {"_instance_2_11": "Foo{x: 12}", "_x_10": "12"}
[debug] QUERY: .(_instance_2_11, foo(), _value_1_12), BINDINGS: {"_instance_2_11": "Foo{x: 12}"}
[debug] LOOKUP: Foo{x: 12}.foo()
[debug] => 13
[debug] QUERY: _value_1_12 = _x_10, BINDINGS: {"_x_10": "12", "_value_1_12": "13"}
[debug] BACKTRACK
[debug] LOOKUP: Foo{x: 12}.foo()
[debug] => No more results.
[debug] BACKTRACK
[debug] RULE:
[debug] f(x) if
[debug] x = 1
[debug] QUERY: _x_13 = 1, BINDINGS: {"_x_13": "12"}
[debug] BACKTRACK
[debug] RULE:
[debug] f(x) if
[debug] x + 1 == 2
[debug] QUERY: _x_14 + 1 and _op_3_15 == 2, BINDINGS: {"_x_14": "12"}
[debug] QUERY: _x_14 + 1, BINDINGS: {"_x_14": "12"}
[debug] MATH: 12 + 1 = _op_3_15, BINDINGS: {}
[debug] QUERY: _op_3_15 == 2, BINDINGS: {"_op_3_15": "13"}
[debug] CMP: 13 == 2, BINDINGS: {}
[debug] BACKTRACK
[debug] HALT
False