chickadee » static-modules

static-modules

Description

static-modules is a Scheme implementation of the module system described by Xavier Leroy in the paper A Modular Module System.

Library Procedures

Identifiers

(ident? X) -> BOOL procedure

Returns #t if X is an identifier, #f otherwise.

(ident-name IDENT) -> STRING procedure

Returns the string name associated with the given identifier.

(ident-stamp IDENT) -> INT procedure

Returns the unique stamp of the given identifier.

(ident-create NAME) -> IDENT procedure

Returns a fresh identifier associated with the given name.

(ident-equal? IDENT IDENT) -> BOOL procedure

Returns #t if the stamps of the given identifiers are equal, #f otherwise.

(ident-empty) -> IDENV procedure

Returns an empty identifier environment.

(ident-add IDENT DATA IDENV) -> IDENV procedure

Adds the given identifier and associated data to the given identifier environment.

(ident-find IDENT IDENV) -> DATA procedure

Looks up the given identifier in the given identifier environment and returns the associated data, or #f if not found.

Access paths

We refer to named types, values (variables), and modules either by identifier (if we are in the scope of their binding) or via the dot notation, e.g. M.x to refer to component x of module M. Access paths represent both kinds of references.

(path? X) -> BOOL procedure

Returns #t if X is an access path, #f otherwise.

(Pident IDENT) -> PATH procedure

Returns a path consisting of the given identifier.

(Pdot PATH STRING) -> PATH procedure

Returns an access path for the given path and field.

(path-equal? PATH PATH) -> BOOL procedure

Returns #t if the two given paths are equal, #f otherwise.

Substitutions

(subst-add IDENT PATH IDENV) -> IDENV procedure

Extends the substition environment with the given identifier and path.

(subst-path PATH IDENV) -> PATH procedure

Applies the given substitutions to the given path.

(subst-identity) -> IDENV procedure

Returns an empty substitution environment.

Abstract syntax for the base language

(make-core-syntax term? valtype? deftype? kind? make-valtype make-deftype subst-valtype subst-deftype subst-kind) procedure

This procedure creates the structure describing base language syntax. The meaning of the fields is as follows:

  • term?: predicate for value expressions
  • valtype?: predicate for type expressions
  • deftype?: predicate for type definitions
  • kind?: predicate for the kinds that a type definition can have
  • make-valtype: constructor for type expressions
  • make-deftype: constructor for type definitions
  • subst-valtype: substitution function for type expressions
  • subst-deftype: substitution function for type definitions
  • subst-kind: substitution function for kinds

Abstract syntax for the module language

(make-mod-syntax core) procedure

This procedure creates the structure describing module language syntax. core is an object created by make-core-syntax. This procedure returns multiple values with the following meaning:

  • modtype? Signature Functorty: predicate and constructors for module type definitions
  • modspec? Value_sig Type_sig Module_sig: predicate and constructors for module type expressions
  • modterm? Modid Structure Functor Mapply Constraint: module term constructors
  • moddef? Value_def Type_def Module_def: predicate and constructor for module definitions
  • subst-modtype subst-modspec subst-typedecl: substitution procedures

Type-checking the base language

(make-core-typing type-term kind-deftype check-valtype check-kind valtype-match deftype-equiv kind-match deftype-of-path) procedure

This procedure creates the structure describing base language type checking. The meaning of the fields is as follows:

  • type-term: the main typing function, which takes a type and an environment, and returns the principal type of the term in the given environment
  • kind-deftype: infers and returns the kind of the given definable type
  • check-valtype check-kind: check the well-formedness of type and kind expressions in the base language
  • valtype-match deftype-equiv kind-match: checking values vs. signatures
  • deftype-of-path: transforms a type path and its kind into the corresponding definable type

Type-checking the module language

(make-mod-typing core-syntax core-typing) procedure

This procedure creates the structure describing module language type checking. core-syntax is an object created by make-core-syntax, and core-typing is an object created by make-core-typing. This procedure returns multiple values with the following meaning:

  • check-modtype: checks the well-formedness of a module type
  • check-signature: checks the well-formedness of a signature
  • type-modterm: infers and returns the type of a module term
  • type-moddef: infers and returns the type of a module definition (sequence of definitions)
  • type-definition: infers and returns the type of a definition (inside a module or at toplevel)

Scoping

This library implements generic scoping pass for the module language. This pass is not described in the paper.

Scoping is the act of associating identifiers with their binding location. We assume that the parser generates fresh identifiers each time it encounters an occurrence of a lexical identifier in the program, and stores those fresh identifiers in the abstract syntax tree it constructs. The scoping pass rewrites the abstract syntax tree to use identical identifiers at a binding site and at all its usage sites.

st-empty procedure

Empty scoping table.

(st-enter-value ID SC) -> SC procedure

Enters a value identifier in the given scoping table.

(st-enter-type ID SC) -> SC procedure

Enters a type identifier in the given scoping table.

(st-enter-module ID SC) -> SC procedure

Enters a module identifier in the given scoping table.

(st-value-path PATH SC) -> PATH procedure
(st-type-path PATH SC) -> PATH procedure
(st-module-path PATH SC) -> PATH procedure
(st-scope-module PATH SC) -> PATH procedure

Evaluation

(make-mod-eval core-syntax core-eval enter-val) procedure

This procedure creates the structure describing module language type checking. core-syntax is an object created by make-core-syntax, and core-eval is a procedure to evalue core syntactic terms. This procedure returns multiple values with the following meaning:

  • modval?: predicate for module values
  • Structure_v: constructor for a structure of values
  • Mclosure_v: constructor for a structure closure
  • path-find-val: given a path and value environment, returns the corresponding value, if it exists in the environment
  • find-module-val: like path-find-val, but only for modules
  • mod-eval: given an evaluation environment and a list of module definitions, evaluates and returns the corresponding value

Version History

License

static-modules is based on the code and paper by Xavier Leroy (2000): A modular module system. Journal of Functional Programming, 10, pp 269-303

Copyright 2010-2013 Ivan Raikov and the Okinawa Institute of
Science and Technology.

This program is free software: you can redistribute it and/or
modify it under the terms of the GNU General Public License as
published by the Free Software Foundation, either version 3 of the
License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

A full copy of the GPL license can be found at
<http://www.gnu.org/licenses/>.

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