Module AbstractCurry.Types

This library contains a definition for representing Curry programs in Curry.

Note this defines a slightly new format for AbstractCurry in comparison to the first proposal of 2003.

Assumption: an abstract Curry program is stored in file with extension .acy

Author: Michael Hanus, Bjoern Peemoeller

Version: September 2015

Summary of exported operations:

version :: String   
Current version of AbstractCurry
preludeName :: String   
The name of the standard prelude.
pre :: String -> (String,String)   
Converts a string into a qualified name of the Prelude.

Exported datatypes:


A module name.

Type synonym: MName = String


The data type for representing qualified names. In AbstractCurry all names are qualified to avoid name clashes. The first component is the module name and the second component the unqualified name as it occurs in the source program. An exception are locally defined names where the module name is the empty string (to avoid name clashes with a globally defined name).

Type synonym: QName = (MName,String)


Data type to specify the visibility of various entities.


  • Public :: CVisibility
  • Private :: CVisibility


Data type for representing a Curry module in the intermediate form. A value of this data type has the form

(CurryProg modname imports typedecls functions opdecls)

where modname: name of this module, imports: list of modules names that are imported, typedecls: Type declarations functions: Function declarations opdecls: Operator precedence declarations



Data type for representing definitions of algebraic data types and type synonyms.

A data type definition of the form

data t x1...xn = ...| c t1....tkc |...

is represented by the Curry term

(CType t v [i1,...,in] [...(CCons c kc v [t1,...,tkc])...])

where each ij is the index of the type variable xj.

Note: the type variable indices are unique inside each type declaration and are usually numbered from 0

Thus, a data type declaration consists of the name of the data type, a list of type parameters and a list of constructor declarations.



The type for representing type variables. They are represented by (i,n) where i is a type variable index which is unique inside a function and n is a name (if possible, the name written in the source program).

Type synonym: CTVarIName = (Int,String)


A constructor declaration consists of the name of the constructor and a list of the argument types of the constructor. The arity equals the number of types.



A record field declaration consists of the name of the the label, the visibility and its corresponding type.



Type expression. A type expression is either a type variable, a function type, or a type constructor application.

Note: the names of the predefined type constructors are "Int", "Float", "Bool", "Char", "IO", "()" (unit type), "(,...,)" (tuple types), "[]" (list type)



Labeled record fields

Type synonym: CField a = (QName,a)


Data type for operator declarations. An operator declaration "fix p n" in Curry corresponds to the AbstractCurry term (COp n fix p).



Data type for operator associativity


  • CInfixOp :: CFixity
  • CInfixlOp :: CFixity
  • CInfixrOp :: CFixity


Function arity

Type synonym: Arity = Int


Data type for representing function declarations.

A function declaration in AbstractCurry is a term of the form

(CFunc name arity visibility type (CRules eval [CRule rule1,...,rulek]))

and represents the function name defined by the rules rule1,...,rulek.

Note: the variable indices are unique inside each rule

Thus, a function declaration consists of the name, arity, type, and a list of rules. The type is the function's type inferred by the type checker. However, if an AbstractCurry program is read with the operation AbstractCurry.Files.readUntypedCurry, the type is either the type signature provided by the programmer or the expression (CTCons ("Prelude","untyped") if the programmer has not provided an explicit type signature.

A function declaration with the constructor CmtFunc is similarly to CFunc but has a comment as an additional first argument. This comment could be used by pretty printers that generate a readable Curry program containing documentation comments.



The general form of a function rule. It consists of a list of patterns (left-hand side) and the right-hand side for these patterns.



Right-hand-side of a CRule or a case expression. It is either a simple unconditional right-hand side or a list of guards with their corresponding right-hand sides, and a list of local declarations.



Data type for representing local (let/where) declarations



Data types for representing object variables. Object variables occurring in expressions are represented by (Var i) where i is a variable index.

Type synonym: CVarIName = (Int,String)


Data type for representing pattern expressions.



Data type for representing Curry expressions.



Data type for representing literals occurring in an expression. It is either an integer, a float, or a character constant.


  • CIntc :: Int -> CLiteral
  • CFloatc :: Float -> CLiteral
  • CCharc :: Char -> CLiteral
  • CStringc :: String -> CLiteral


Data type for representing statements in do expressions and list comprehensions.



Type of case expressions


  • CRigid :: CCaseType
  • CFlex :: CCaseType

Exported operations:

version :: String   

Current version of AbstractCurry

Further infos:
  • solution complete, i.e., able to compute all solutions

preludeName :: String   

The name of the standard prelude.

Further infos:
  • solution complete, i.e., able to compute all solutions

pre :: String -> (String,String)   

Converts a string into a qualified name of the Prelude.

Further infos:
  • solution complete, i.e., able to compute all solutions