added inference context
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@ -0,0 +1,228 @@
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use super::TopLevelContext;
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use crate::typedef::*;
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use std::boxed::Box;
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use std::collections::HashMap;
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struct ContextStack<'a> {
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/// stack level, starts from 0
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level: u32,
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/// stack of variable definitions containing (id, def, level) where `def` is the original
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/// definition in `level-1`.
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var_defs: Vec<(usize, VarDef<'a>, u32)>,
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/// stack of symbol definitions containing (name, level) where `level` is the smallest level
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/// where the name is assigned a value
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sym_def: Vec<(&'a str, u32)>,
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}
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pub struct InferenceContext<'a> {
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/// top level context
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top_level: TopLevelContext<'a>,
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/// list of primitive instances
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primitives: Vec<Type>,
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/// list of variable instances
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variables: Vec<Type>,
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/// identifier to (type, readable) mapping.
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/// an identifier might be defined earlier but has no value (for some code path), thus not
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/// readable.
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sym_table: HashMap<&'a str, (Type, bool)>,
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/// resolution function reference, that may resolve unbounded identifiers to some type
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resolution_fn: Box<dyn FnMut(&str) -> Result<Type, String>>,
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/// stack
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stack: ContextStack<'a>,
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}
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// non-trivial implementations here
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impl<'a> InferenceContext<'a> {
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/// return a new `InferenceContext` from `TopLevelContext` and resolution function.
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pub fn new(
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top_level: TopLevelContext,
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resolution_fn: Box<dyn FnMut(&str) -> Result<Type, String>>,
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) -> InferenceContext {
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let primitives = (0..top_level.primitive_defs.len())
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.map(|v| TypeEnum::PrimitiveType(PrimitiveId(v)).into())
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.collect();
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let variables = (0..top_level.var_defs.len())
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.map(|v| TypeEnum::TypeVariable(VariableId(v)).into())
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.collect();
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InferenceContext {
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top_level,
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primitives,
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variables,
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sym_table: HashMap::new(),
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resolution_fn,
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stack: ContextStack {
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level: 0,
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var_defs: Vec::new(),
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sym_def: Vec::new(),
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},
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}
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}
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/// execute the function with new scope.
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/// variable assignment would be limited within the scope (not readable outside), and type
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/// variable type guard would be limited within the scope.
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/// returns the list of variables assigned within the scope, and the result of the function
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pub fn with_scope<F, R>(&mut self, f: F) -> (Vec<&'a str>, R)
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where
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F: FnOnce(&mut Self) -> R,
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{
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self.stack.level += 1;
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let result = f(self);
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self.stack.level -= 1;
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while !self.stack.var_defs.is_empty() {
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let (_, _, level) = self.stack.var_defs.last().unwrap();
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if *level > self.stack.level {
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let (id, def, _) = self.stack.var_defs.pop().unwrap();
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self.top_level.var_defs[id] = def;
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} else {
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break;
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}
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}
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let mut poped_names = Vec::new();
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while !self.stack.sym_def.is_empty() {
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let (_, level) = self.stack.sym_def.last().unwrap();
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if *level > self.stack.level {
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let (name, _) = self.stack.sym_def.pop().unwrap();
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self.sym_table.remove(name).unwrap();
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poped_names.push(name);
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} else {
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break;
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}
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}
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(poped_names, result)
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}
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/// assign a type to an identifier.
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/// may return error if the identifier was defined but with different type
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pub fn assign(&mut self, name: &'a str, ty: Type) -> Result<Type, String> {
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if let Some((t, x)) = self.sym_table.get_mut(name) {
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if t == &ty {
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if !*x {
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self.stack.sym_def.push((name, self.stack.level));
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}
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*x = true;
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Ok(ty)
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} else {
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Err("different types".into())
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}
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} else {
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self.stack.sym_def.push((name, self.stack.level));
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self.sym_table.insert(name, (ty.clone(), true));
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Ok(ty)
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}
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}
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/// check if an identifier is already defined
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pub fn defined(&self, name: &str) -> bool {
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self.sym_table.get(name).is_some()
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}
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/// get the type of an identifier
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/// may return error if the identifier is not defined, and cannot be resolved with the
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/// resolution function.
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pub fn resolve(&mut self, name: &str) -> Result<Type, String> {
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if let Some((t, x)) = self.sym_table.get(name) {
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if *x {
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Ok(t.clone())
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} else {
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Err("may not have value".into())
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}
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} else {
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self.resolution_fn.as_mut()(name)
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}
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}
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/// restrict the bound of a type variable by replacing its definition.
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/// used for implementing type guard
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pub fn restrict(&mut self, id: VariableId, mut def: VarDef<'a>) {
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std::mem::swap(self.top_level.var_defs.get_mut(id.0).unwrap(), &mut def);
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self.stack.var_defs.push((id.0, def, self.stack.level));
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}
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}
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// trivial getters:
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impl<'a> InferenceContext<'a> {
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pub fn get_primitive(&self, id: PrimitiveId) -> Type {
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self.primitives.get(id.0).unwrap().clone()
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}
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pub fn get_variable(&self, id: VariableId) -> Type {
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self.variables.get(id.0).unwrap().clone()
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}
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pub fn get_fn_def(&self, name: &str) -> Option<&FnDef> {
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self.top_level.fn_table.get(name)
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}
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pub fn get_primitive_def(&self, id: PrimitiveId) -> &TypeDef {
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self.top_level.primitive_defs.get(id.0).unwrap()
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}
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pub fn get_class_def(&self, id: ClassId) -> &ClassDef {
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self.top_level.class_defs.get(id.0).unwrap()
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}
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pub fn get_parametric_def(&self, id: ParamId) -> &ParametricDef {
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self.top_level.parametric_defs.get(id.0).unwrap()
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}
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pub fn get_variable_def(&self, id: VariableId) -> &VarDef {
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self.top_level.var_defs.get(id.0).unwrap()
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}
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pub fn get_type(&self, name: &str) -> Option<Type> {
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self.top_level.get_type(name)
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}
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}
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impl TypeEnum {
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pub fn subst(&self, map: &HashMap<VariableId, Type>) -> TypeEnum {
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match self {
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TypeEnum::TypeVariable(id) => map.get(id).map(|v| v.as_ref()).unwrap_or(self).clone(),
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TypeEnum::ParametricType(id, params) => TypeEnum::ParametricType(
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*id,
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params
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.iter()
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.map(|v| v.as_ref().subst(map).into())
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.collect(),
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),
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_ => self.clone(),
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}
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}
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pub fn inv_subst(&self, map: &[(Type, Type)]) -> Type {
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for (from, to) in map.iter() {
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if self == from.as_ref() {
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return to.clone();
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}
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}
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match self {
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TypeEnum::ParametricType(id, params) => TypeEnum::ParametricType(
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*id,
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params.iter().map(|v| v.as_ref().inv_subst(map)).collect(),
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),
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_ => self.clone(),
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}
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.into()
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}
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pub fn get_subst(&self, ctx: &InferenceContext) -> HashMap<VariableId, Type> {
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match self {
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TypeEnum::ParametricType(id, params) => {
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let vars = &ctx.get_parametric_def(*id).params;
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vars.iter()
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.zip(params)
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.map(|(v, p)| (*v, p.as_ref().clone().into()))
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.collect()
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}
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// if this proves to be slow, we can use option type
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_ => HashMap::new(),
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}
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}
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pub fn get_base<'b: 'a, 'a>(&'a self, ctx: &'b InferenceContext) -> Option<&'b TypeDef> {
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match self {
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TypeEnum::PrimitiveType(id) => Some(ctx.get_primitive_def(*id)),
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TypeEnum::ClassType(id) | TypeEnum::VirtualClassType(id) => {
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Some(&ctx.get_class_def(*id).base)
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}
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TypeEnum::ParametricType(id, _) => Some(&ctx.get_parametric_def(*id).base),
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_ => None,
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}
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}
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}
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@ -1,2 +1,4 @@
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mod inference_context;
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mod top_level_context;
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pub use inference_context::InferenceContext;
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pub use top_level_context::TopLevelContext;
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