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A compiler for generating reliability artifacts from service expectation definitions.
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src/caffeine_query_language/resolver.gleam
import caffeine_lang/errors.{type CompilationError}
import caffeine_query_language/ast.{type Comparator, type CqlParsed, type Exp}
import gleam/bool
import gleam/float
/// Supported primitive query types that can be resolved from CQL expressions.
/// Each primitive represents a specific SLO calculation pattern.
pub type Primitives {
/// Good over total requires a top level division operator.
/// Represents an SLO where the numerator is the "good" events
/// and the denominator is the "total" events.
GoodOverTotal(numerator: Exp(CqlParsed), denominator: Exp(CqlParsed))
TimeSlice(
comparator: Comparator,
interval_in_seconds: Int,
threshold: Float,
query: String,
)
}
/// Resolves a parsed CQL expression into a primitive type.
/// Supports GoodOverTotal (division at the top level) and TimeSlice.
/// Returns an error if the expression doesn't match a known primitive pattern.
@internal
pub fn resolve_primitives(
exp: Exp(CqlParsed),
) -> Result(Primitives, CompilationError) {
case exp {
ast.OperatorExpr(left, right, ast.Div) -> {
// Check that neither operand contains a time_slice expression
use <- bool.guard(
when: contains_time_slice(left) || contains_time_slice(right),
return: Error(errors.cql_resolver_error(
msg: "time_slice cannot be used as an operand. It must be the entire expression.",
)),
)
Ok(GoodOverTotal(left, right))
}
ast.TimeSliceExpr(spec) ->
Ok(TimeSlice(
comparator: spec.comparator,
interval_in_seconds: float.truncate(spec.interval_seconds),
threshold: spec.threshold,
query: spec.query,
))
_ ->
Error(errors.cql_resolver_error(
msg: "Invalid expression. Expected a top level division operator or time_slice.",
))
}
}
/// Checks if an expression contains a time_slice expression anywhere.
fn contains_time_slice(exp: Exp(a)) -> Bool {
case exp {
ast.TimeSliceExpr(_) -> True
ast.OperatorExpr(left, right, _) ->
contains_time_slice(left) || contains_time_slice(right)
ast.Primary(ast.PrimaryExp(inner)) -> contains_time_slice(inner)
ast.Primary(ast.PrimaryWord(_)) -> False
}
}