Module type_expr 

Type expression utilities for Mangle’s structural type system.

Type expressions are represented as IR instructions (Inst::ApplyFn for compound types, Inst::Name for base types). This module provides:

• Predicates (is_struct_type, is_union_type, etc.)
• Accessors (struct_type_field, list_type_arg, etc.)
• Wellformedness validation (wellformed_type)
• Type conformance (set_conforms, type_conforms)
• HasType runtime validation (has_type)
• TaggedUnion expansion

Constants

FN_EMPTY_TYPE

FN_FUN

FN_LIST

FN_MAP

FN_OPT

FN_OPTION

FN_PAIR

FN_REL

FN_SINGLETON

FN_STRUCT

FN_TAGGED_UNION

FN_TUPLE

FN_UNION

Functions

apply_subst

Applies a substitution (type variable -> type) to a type expression. Returns a new InstId with all type variables replaced.

collect_vars

Collects all type variables from a type expression into a set.

empty_type

Creates or finds the empty type sentinel fn:EmptyType().

expand_tagged_union_for_bounds

Like expand_tagged_union_type but uses /name instead of fn:Singleton for the tag field type. This is less precise but compatible with the bounds checker’s type inference (which infers /name for name constants in facts).

expand_tagged_union_type

Expands fn:TaggedUnion(tag_field, tag1, struct1, tag2, struct2, ...) into fn:Union(fn:Struct(tag_field, fn:Singleton(tag1), ...fields1), ...).

find_or_create_name

Finds or creates a Name instruction in the IR.

get_type_context

Gets the type context (all type variables mapped to /any) from the type variables appearing in a type expression.

has_type

Checks if a concrete IR constant value matches a type expression.

intersect_type

Computes the intersection (greatest lower bound) of two type expressions.

is_any

True if this is /any.

is_base_type

True if this is a base type name constant (e.g. /number, /string, /any).

is_empty_type

True if this is the empty type sentinel fn:EmptyType().

is_fun_type

is_list_type

is_map_type

is_name_const

True if this is a Inst::Name (any name constant, including base types and user-defined name hierarchy members like /animal/dog).

is_opt_field

is_option_type

is_pair_type

is_rel_type

is_singleton_type

is_struct_type

is_tagged_union_type

is_tuple_type

is_type_var

True if this is a type variable (Inst::Var).

is_union_type

list_type_arg

Returns the element type of a fn:List type expression.

lower_bound

Computes the lower bound (most general common subtype) of a set of type expressions.

map_type_args

Returns (key_type, value_type) of a fn:Map type expression.

new_list_type

Creates a fn:List(elem_type) type expression.

new_map_type

Creates a fn:Map(key_type, val_type) type expression.

new_rel_type

Builds a fn:Rel(t1, t2, ...) type from a slice of argument types.

new_struct_type

Creates a fn:Struct(field1, type1, ...) type expression.

new_tuple_type

Creates a fn:Tuple(t1, t2, ...) type expression.

new_union_or_single

Builds fn:Union(alts...) or returns the single type if only one.

rel_type_alternatives

Extracts alternatives from a possibly-union-wrapped relation type.

rel_type_args

Extracts the argument types from a fn:Rel(t1, t2, ...).

rel_type_from_alternatives

Creates a single relation type or union from a list of alternatives.

rel_types_from_decl

Builds fn:Rel types from declaration bounds. Each BoundDecl becomes one fn:Rel.

remove_from_union_type

Removes types conforming to to_remove from a union type. Returns the remaining union, or EmptyType if nothing remains.

set_conforms

Checks if left set-conforms to right.

struct_type_field

Returns the type of a struct field by name (simple struct only).

struct_type_field_deep

Returns the type of a struct field by name. Handles Struct, Union, and TaggedUnion by projecting the field from each alternative and returning their upper bound.

struct_type_fields

Iterates struct type args, yielding (field_name_id, field_type_id, is_optional).

tagged_union_tag_field

Returns the tag field InstId (a Name) of a fn:TaggedUnion.

tagged_union_variants

Returns (tags, variant_struct_types) for a fn:TaggedUnion. Tags are at odd indices starting from 1, variant structs at even indices from 2.

type_conforms

Checks structural type conformance (non-union, non-tagged-union).

union_type_args

Returns the alternative type expressions of a fn:Union.

upper_bound

Computes the upper bound (least common supertype) of a set of type expressions.

wellformed_type

Validates that a type expression is well-formed.

Type Aliases

TypeContext

Type variable context: maps variable NameId to its bound (an InstId type expr).