Use Parameter type alias for HashMap<String, ParameterValue>.

src/execute/scale.rs

@@ -1416,7 +1416,7 @@ pub fn apply_oob_to_column_discrete(
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::plot::ArrayElement;
+    use crate::plot::{ArrayElement, Parameters};
     use crate::Geom;
     use arrow::datatypes::DataType;
 
@@ -1722,8 +1722,8 @@ mod tests {
         spec.project = Some(Projection {
             coord,
             aesthetics,
-            properties: std::collections::HashMap::new(),
-            computed: std::collections::HashMap::new(),
+            properties: Parameters::new(),
+            computed: Parameters::new(),
         });
 
         // Create scale for pos2 (theta in polar) without explicit expand

src/lib.rs

@@ -55,7 +55,7 @@ pub mod validate;
 
 // Re-export key types for convenience
 pub use plot::{
-    AestheticValue, DataSource, Facet, FacetLayout, Geom, Layer, Mappings, Plot, Scale,
+    AestheticValue, DataSource, Facet, FacetLayout, Geom, Layer, Mappings, Parameters, Plot, Scale,
     SqlExpression,
 };
 

src/parser/builder.rs

@@ -453,7 +453,7 @@ fn build_layer(node: &Node, source: &SourceTree) -> Result<Layer> {
     let mut geom = Geom::point(); // default
     let mut aesthetics = Mappings::new();
     let mut remappings = Mappings::new();
-    let mut parameters = HashMap::new();
+    let mut parameters = Parameters::new();
     let mut partition_by = Vec::new();
     let mut filter = None;
     let mut order_by = None;
@@ -542,11 +542,8 @@ fn build_place_layer(node: &Node, source: &SourceTree) -> Result<Layer> {
 }
 
 /// Parse a setting_clause: SETTING param => value, ...
-fn parse_setting_clause(
-    node: &Node,
-    source: &SourceTree,
-) -> Result<HashMap<String, ParameterValue>> {
-    let mut parameters = HashMap::new();
+fn parse_setting_clause(node: &Node, source: &SourceTree) -> Result<Parameters> {
+    let mut parameters = Parameters::new();
 
     // Find all parameter_assignment nodes
     let query = "(parameter_assignment) @param";
@@ -671,7 +668,7 @@ fn build_scale(node: &Node, source: &SourceTree) -> Result<Scale> {
     let mut output_range: Option<OutputRange> = None;
     let mut transform: Option<Transform> = None;
     let mut explicit_transform = false;
-    let mut properties = HashMap::new();
+    let mut properties = Parameters::new();
     let mut label_mapping: Option<HashMap<String, Option<String>>> = None;
     let mut label_template = "{}".to_string();
 
@@ -904,7 +901,7 @@ fn parse_scale_renaming_clause(
 fn build_facet(node: &Node, source: &SourceTree) -> Result<Facet> {
     let mut row_vars = Vec::new();
     let mut column_vars = Vec::new();
-    let mut properties = HashMap::new();
+    let mut properties = Parameters::new();
 
     let mut cursor = node.walk();
     let mut next_vars_are_cols = false;
@@ -971,7 +968,7 @@ fn parse_facet_vars(node: &Node, source: &SourceTree) -> Result<Vec<String>> {
 /// Aesthetics are optional and default to the coord's standard names.
 fn build_project(node: &Node, source: &SourceTree) -> Result<Projection> {
     let mut coord_type_name: Option<String> = None;
-    let mut properties = HashMap::new();
+    let mut properties = Parameters::new();
     let mut user_aesthetics: Option<Vec<String>> = None;
 
     let mut cursor = node.walk();
@@ -1032,7 +1029,7 @@ fn build_project(node: &Node, source: &SourceTree) -> Result<Projection> {
         coord,
         aesthetics,
         properties,
-        computed: HashMap::new(),
+        computed: Parameters::new(),
     })
 }
 
@@ -1096,18 +1093,15 @@ fn parse_single_project_property(
 fn validate_project_properties(
     coord: &Coord,
     coord_type_name: Option<&str>,
-    properties: &HashMap<String, ParameterValue>,
+    properties: &Parameters,
 ) -> Result<()> {
     coord
         .resolve_properties(coord_type_name, properties)
         .map_err(GgsqlError::ParseError)?;
     Ok(())
 }
 
-fn parse_coord_system(
-    name: Option<&str>,
-    properties: &HashMap<String, ParameterValue>,
-) -> Result<Coord> {
+fn parse_coord_system(name: Option<&str>, properties: &Parameters) -> Result<Coord> {
     use crate::plot::projection::coord::map_projections::NAMED_PROJECTIONS;
     match name {
         Some("cartesian") | None => Ok(Coord::cartesian()),

src/plot/facet/types.rs

@@ -2,10 +2,9 @@
 //!
 //! This module defines faceting configuration for small multiples.
 
-use crate::plot::types::{DefaultParamValue, ParamConstraint, ParamDefinition};
+use crate::plot::types::{DefaultParamValue, ParamConstraint, ParamDefinition, Parameters};
 use crate::plot::ParameterValue;
 use serde::{Deserialize, Serialize};
-use std::collections::HashMap;
 
 /// Faceting specification (from FACET clause)
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
@@ -15,7 +14,7 @@ pub struct Facet {
     /// Properties from SETTING clause (e.g., scales, ncol, missing)
     /// After resolution, includes validated and defaulted values
     #[serde(default)]
-    pub properties: HashMap<String, ParameterValue>,
+    pub properties: Parameters,
     /// Whether properties have been resolved (validated and defaults applied)
     #[serde(skip, default)]
     pub resolved: bool,
@@ -41,7 +40,7 @@ impl Facet {
     pub fn new(layout: FacetLayout) -> Self {
         Self {
             layout,
-            properties: HashMap::new(),
+            properties: Parameters::new(),
             resolved: false,
         }
     }

src/plot/layer/geom/area.rs

@@ -1,7 +1,7 @@
 //! Area geom implementation
 
 use crate::plot::layer::orientation::{ALIGNED, ORIENTATION_VALUES};
-use crate::plot::types::DefaultAestheticValue;
+use crate::plot::types::{DefaultAestheticValue, Parameters};
 use crate::plot::{DefaultParamValue, ParamDefinition};
 use crate::Mappings;
 
@@ -66,7 +66,7 @@ impl GeomTrait for Area {
         schema: &crate::plot::Schema,
         aesthetics: &Mappings,
         group_by: &[String],
-        parameters: &std::collections::HashMap<String, crate::plot::ParameterValue>,
+        parameters: &Parameters,
         _execute_query: &dyn Fn(&str) -> crate::Result<crate::DataFrame>,
         dialect: &dyn crate::reader::SqlDialect,
         aesthetic_ctx: &crate::plot::aesthetic::AestheticContext,

src/plot/layer/geom/bar.rs

@@ -1,6 +1,5 @@
 //! Bar geom implementation
 
-use std::collections::HashMap;
 use std::collections::HashSet;
 
 use super::stat_aggregate;
@@ -10,7 +9,7 @@ use super::{
     ParamConstraint, ParamDefinition, StatResult,
 };
 use crate::naming;
-use crate::plot::types::{DefaultAestheticValue, ParameterValue};
+use crate::plot::types::{DefaultAestheticValue, Parameters};
 use crate::reader::SqlDialect;
 use crate::{DataFrame, GgsqlError, Mappings, Result};
 
@@ -90,7 +89,7 @@ impl GeomTrait for Bar {
         schema: &Schema,
         aesthetics: &Mappings,
         group_by: &[String],
-        parameters: &HashMap<String, ParameterValue>,
+        parameters: &Parameters,
         _execute_query: &dyn Fn(&str) -> Result<DataFrame>,
         dialect: &dyn SqlDialect,
         aesthetic_ctx: &crate::plot::aesthetic::AestheticContext,

src/plot/layer/geom/boxplot.rs

@@ -1,14 +1,12 @@
 //! Boxplot geom implementation
 
-use std::collections::HashMap;
-
 use super::types::{wrap_with_dummy_axis, POSITION_VALUES, SIDE_VALUES};
 use super::{DefaultAesthetics, GeomTrait, GeomType};
 use crate::{
     naming,
     plot::{
         geom::types::get_column_name, DefaultAestheticValue, DefaultParamValue, ParamConstraint,
-        ParamDefinition, ParameterValue, StatResult,
+        ParamDefinition, ParameterValue, Parameters, StatResult,
     },
     reader::SqlDialect,
     DataFrame, GgsqlError, Mappings, Result,
@@ -101,7 +99,7 @@ impl GeomTrait for Boxplot {
         _schema: &crate::plot::Schema,
         aesthetics: &Mappings,
         group_by: &[String],
-        parameters: &HashMap<String, ParameterValue>,
+        parameters: &Parameters,
         _execute_query: &dyn Fn(&str) -> Result<DataFrame>,
         dialect: &dyn SqlDialect,
         aesthetic_ctx: &crate::plot::aesthetic::AestheticContext,
@@ -127,7 +125,7 @@ fn stat_boxplot(
     query: &str,
     aesthetics: &Mappings,
     group_by: &[String],
-    parameters: &HashMap<String, ParameterValue>,
+    parameters: &Parameters,
     dialect: &dyn SqlDialect,
     aesthetic_ctx: &crate::plot::aesthetic::AestheticContext,
 ) -> Result<StatResult> {
@@ -340,6 +338,7 @@ fn boxplot_sql_append_outliers(
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::plot::Parameters;
     use crate::reader::AnsiDialect;
 
     // ==================== SQL Generation Tests (Compact) ====================
@@ -639,7 +638,7 @@ mod tests {
             "pos2".to_string(),
             AestheticValue::standard_column("value".to_string()),
         );
-        let mut parameters: HashMap<String, ParameterValue> = HashMap::new();
+        let mut parameters = Parameters::new();
         parameters.insert("coef".to_string(), ParameterValue::Number(1.5));
         parameters.insert("outliers".to_string(), ParameterValue::Boolean(true));
 

src/plot/layer/geom/density.rs

@@ -6,13 +6,11 @@ use crate::{
     naming,
     plot::{
         geom::types::get_column_name, DefaultAestheticValue, DefaultParamValue, ParamConstraint,
-        ParamDefinition, ParameterValue, StatResult,
+        ParamDefinition, ParameterValue, Parameters, StatResult,
     },
     reader::SqlDialect,
     GgsqlError, Mappings, Result,
 };
-use std::collections::HashMap;
-
 /// Gaussian kernel normalization constant: 1/sqrt(2*pi)
 /// Precomputed at compile time to avoid repeated SQRT and PI() calls in SQL
 const GAUSSIAN_NORM: f64 = 0.3989422804014327; // 1.0 / (2.0 * std::f64::consts::PI).sqrt()
@@ -104,7 +102,7 @@ impl GeomTrait for Density {
         _schema: &crate::plot::Schema,
         aesthetics: &Mappings,
         group_by: &[String],
-        parameters: &std::collections::HashMap<String, crate::plot::ParameterValue>,
+        parameters: &Parameters,
         _execute_query: &dyn Fn(&str) -> crate::Result<crate::DataFrame>,
         dialect: &dyn SqlDialect,
         aesthetic_ctx: &crate::plot::aesthetic::AestheticContext,
@@ -154,7 +152,7 @@ pub(crate) fn stat_density(
     value_aesthetic: &str,
     smooth_aesthetic: Option<&str>,
     group_by: &[String],
-    parameters: &HashMap<String, ParameterValue>,
+    parameters: &Parameters,
     dialect: &dyn SqlDialect,
     aesthetic_ctx: &crate::plot::aesthetic::AestheticContext,
 ) -> Result<StatResult> {
@@ -214,7 +212,7 @@ fn density_sql_bandwidth(
     from: &str,
     groups: &[String],
     value: &str,
-    parameters: &HashMap<String, ParameterValue>,
+    parameters: &Parameters,
     dialect: &dyn SqlDialect,
 ) -> String {
     let adjust = match parameters.get("adjust") {
@@ -279,10 +277,7 @@ fn silverman_rule(
     format!("{adjust} * {min_expr} * POW(COUNT(*), -0.2)")
 }
 
-fn choose_kde_kernel(
-    parameters: &HashMap<String, ParameterValue>,
-    smooth: Option<String>,
-) -> Result<String> {
+fn choose_kde_kernel(parameters: &Parameters, smooth: Option<String>) -> Result<String> {
     let kernel = match parameters.get("kernel") {
         Some(ParameterValue::String(krnl)) => krnl.as_str(),
         _ => {
@@ -609,6 +604,7 @@ fn compute_density(
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::plot::Parameters;
     use crate::reader::duckdb::DuckDBReader;
     use crate::reader::AnsiDialect;
     use crate::reader::Reader;
@@ -618,7 +614,7 @@ mod tests {
     fn test_density_sql_no_groups() {
         let query = "SELECT x FROM (VALUES (1.0), (2.0), (3.0)) AS t(x)";
         let groups: Vec<String> = vec![];
-        let mut parameters = HashMap::new();
+        let mut parameters = Parameters::new();
         parameters.insert("bandwidth".to_string(), ParameterValue::Number(0.5));
         parameters.insert(
             "kernel".to_string(),
@@ -694,7 +690,7 @@ mod tests {
     fn test_density_sql_with_two_groups() {
         let query = "SELECT x, region, category FROM (VALUES (1.0, 'A', 'X'), (2.0, 'B', 'Y')) AS t(x, region, category)";
         let groups = vec!["region".to_string(), "category".to_string()];
-        let mut parameters = HashMap::new();
+        let mut parameters = Parameters::new();
         parameters.insert("bandwidth".to_string(), ParameterValue::Number(0.5));
         parameters.insert(
             "kernel".to_string(),
@@ -816,7 +812,7 @@ mod tests {
         // Test 1: No groups
         let query = "SELECT x FROM (VALUES (1.0), (2.0), (3.0), (4.0), (5.0)) AS t(x)";
         let groups: Vec<String> = vec![];
-        let parameters = HashMap::new(); // No explicit bandwidth - will compute
+        let parameters = Parameters::new(); // No explicit bandwidth - will compute
 
         let bw_cte = density_sql_bandwidth(query, &groups, "x", &parameters, &AnsiDialect);
 
@@ -872,7 +868,7 @@ mod tests {
     fn test_kernel_integration(kernel_name: &str, tolerance: f64) {
         let query = "SELECT x FROM (VALUES (1.0), (2.0), (3.0), (4.0), (5.0)) AS t(x)";
         let groups: Vec<String> = vec![];
-        let mut parameters = HashMap::new();
+        let mut parameters = Parameters::new();
         parameters.insert("bandwidth".to_string(), ParameterValue::Number(1.0));
         parameters.insert(
             "kernel".to_string(),
@@ -968,7 +964,7 @@ mod tests {
 
     #[test]
     fn test_kernel_invalid() {
-        let mut parameters = HashMap::new();
+        let mut parameters = Parameters::new();
         parameters.insert(
             "kernel".to_string(),
             ParameterValue::String("invalid_kernel".to_string()),
@@ -991,7 +987,7 @@ mod tests {
         // Compare weighted and unweighted results
         let query = "SELECT x FROM (VALUES (1.0), (2.0), (3.0)) AS t(x)";
         let groups: Vec<String> = vec![];
-        let mut parameters = HashMap::new();
+        let mut parameters = Parameters::new();
         parameters.insert("bandwidth".to_string(), ParameterValue::Number(0.5));
         parameters.insert(
             "kernel".to_string(),
@@ -1148,7 +1144,7 @@ mod tests {
 
         let query = "SELECT x FROM bench_data";
         let groups: Vec<String> = vec![];
-        let mut parameters = HashMap::new();
+        let mut parameters = Parameters::new();
         parameters.insert("bandwidth".to_string(), ParameterValue::Number(5.0));
         parameters.insert(
             "kernel".to_string(),
@@ -1197,7 +1193,7 @@ mod tests {
     #[test]
     fn stat_density_missing_value_aesthetic_emits_user_facing_name() {
         let mappings = crate::Mappings::new();
-        let parameters = std::collections::HashMap::new();
+        let parameters = Parameters::new();
         let dialect = AnsiDialect;
         let ctx = crate::plot::aesthetic::AestheticContext::from_static(&["x", "y"], &[]);