FlatCurry: An intermediate language for Curry programs

This package contains libraries to deal with FlatCurry programs. FlatCurry is an intermediate language to represent Curry programs where a lot of syntactic sugar has been eliminated. In particular, operations defined by general rules with local declarations and pattern matching are represented in FlatCurry by a single rule containing case expressions and disjunctions in its right-hand side. The precise structure of FlatCurry is defined in the module FlatCurry.Types.

Usage of FlatCurry

Usually, the front end of Curry systems (like PAKCS or KiCS2) translates a Curry program into an intermediate FlatCurry program in order to further compile it into the target code. Furthermore, the FlatCurry representation is used to analyze or verify properties of Curry programs. When implementing such Curry language tools, it is important to understand the FlatCurry representation and how it is obtained from a Curry program. For this purpose, one can use the Curry browser which has options to show the FlatCurry representation of a Curry program in various forms. One can also the Curry front end to print the FlatCurry representation in a human-readable format. For this purpose, one could add the line

{-# OPTIONS_FRONTEND -ddump-flat #-}

at the beginning of a Curry program.

Type declarations in FlatCurry

Note that definition of types introduced by data or newtype declarations are still present in FlatCurry. Although a newtype declaration can be considered as syntactic sugar for a type synonym, a newtype declaration is important for typing reasons, i.e., a newtype is different from a type synonym. Thus, if one wants to translate FlatCurry programs into typed target languages (e.g., Haskell), the information about a newtype might be relevant. However, if the target language is untyped, every use of a newtype can be eliminated by dropping the newtype constructors in the FlatCurry program. This can be done by operations provided by the module FlatCurry.ElimNewtype.

Modules of the package

Currently, this package contains the following modules:

• FlatCurry.Compact: This module contains operations to reduce the size of FlatCurry programs by combining the main module and all imports into a single program that contains only the operations directly or indirectly called from a set of main operations.
• FlatCurry.ElimNewtype: This module contains operations to eliminate definitions and uses of newtype in a FlatCurry program.
• FlatCurry.Files: This module defines operations to read and write FlatCurry programs.
• FlatCurry.FlexRigid: provides an operation to compute the rigid/flex status of a FlatCurry expression (typically, the right-hand side of a rule).
• FlatCurry.Goodies: This library provides selector operations, test and update operations as well as some useful auxiliary operations for FlatCurry data terms.
• FlatCurry.Normalize: This module contains operations to transform FlatCurry entities into some normalized form so that they can be easier compared for equivalence.
• FlatCurry.Pretty: This library provides pretty-printers for FlatCurry modules and all substructures (e.g., expressions).
• FlatCurry.Read: This library defines operations to read FlatCurry programs or interfaces together with all its imported modules in the current load path.
• FlatCurry.Show: This library contains operations to transform FlatCurry programs into string representations, either in a FlatCurry format or in a Curry-like syntax.
• FlatCurry.Types: This module defines the data types to represent FlatCurry programs in Curry.
• FlatCurry.XML: This module contains operations to convert FlatCurry programs into corresponding XML expressions and vice versa. This can be used to store Curry programs in a way independent of a Curry system or to use a Curry system, like PAKCS, as back end by other functional logic programming systems.