Amulet 0.4.0.0 "Open Import Tariffs.ml"

Note: Amulet now needs multiple files to work correctly. Please refer to the installation instructions for information on how to set it up.

Changes since the last release:

• The note informing the programmer when a match can be safely converted into a let (similarly for function/fun) is now properly generated.

• Breaking: Applications of type functions and polymorphic types are disallowed in instance heads.

• There is now built-in syntax for using Applicative functors. The syntax (| f x y z |) (called an idiom bracket) desugars to pure f <*> x <*> y <*> z, using whatever pure and (<*>) are in scope. See the paper that introduced Applicative for more details.

• Amulet has a new module system: see below.

• The compiler driver was changed to use sub-commands instead of the mess of flags we had before. See amc --help for more details.

• The compiler driver and the REPL can print their version, including which commit the release was generated from.

• Minor changes to the constraint solver should help with type function behaviour in instance definitions.

• Some operator precedence issues were fixed in the Lua parser. Moreover, the backend will print if statements in a single line when possible.

• An issue relating to sharing clauses in pattern lowering was fixed, thus generating faster code (at the expense of uglier-looking Lua)

Amulet's New Module System

The old module system (which treated modules as extensible namespaces) was completely replaced by a proper, saner module system:

• Modules can no longer be extended—redefining a module will shadow it, as with any other definition. As a result, declaring a nested module (i.e. module X.Y = begin .. end) is no longer valid.

• External files can be imported, and treated as another module using the import construct. This supports both resolution according to a library path (import "my_lib.ml"), or relative to the current file (import "./my_lib.ml").

• As the module language is now more unified, import module terms can also be used within let open expressions.

• Most of the built-ins were axed from the compiler and moved to a ML file, except for those that need special type checker syntax. The prelude is loaded automatically in the REPL, but needs to be imported explicitly in compiled code: open import "prelude.ml" results in the old compiler behaviour w.r.t. builtin names.

• There are bindings to some Lua libraries under the lua/ directory of the standard library.

• The REPL now has a :compile command for writing the currently-loaded code to a file.