HASKELL98 REPORT PDF

A module implementation may only export an entity that it declares, or that it imports from some other module. If the export list is omitted, all values, types and classes defined in the module are exported, but not those that are imported. Entities in an export list may be named as follows: A value, field name, or class method, whether declared in the module body or imported, may be named by giving the name of the value as a qvarid, which must be in scope. Operators should be enclosed in parentheses to turn them into qvarids. An algebraic datatype T declared by a data or newtype declaration may be named in one of three ways: The form T names the type but not the constructors or field names.

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All patterns must be linear no variable may appear more than once. It is as if an identifier not used elsewhere were put in its place. Attempting to match a pattern can have one of three results: it may fail; it may succeed, returning a binding for each variable in the pattern; or it may diverge i.

Pattern matching proceeds from left to right, and outside to inside, according to the following rules: Matching the pattern var against a value v always succeeds and binds var to v. Binding does not imply evaluation. At that point the entire pattern is matched against the value, and if the match fails or diverges, so does the overall computation. Matching the pattern con pat against a value, where con is a constructor defined by newtype, depends on the value: If the value is of the form con v, then pat is matched against v.

That is, constructors associated with newtype serve only to change the type of a value. Matching the pattern con pat Matching against a constructor using labeled fields is the same as matching ordinary constructor patterns except that the fields are matched in the order they are named in the field list. All fields listed must be declared by the constructor; fields may not be named more than once.

The match diverges if this test diverges. The interpretation of numeric literals is exactly as described in Section 3. The match diverges if the comparison diverges. The interpretation of the literal k is the same as in numeric literal patterns, except that only integer literals are allowed. Matching an as-pattern var apat against a value v is the result of matching apat against v, augmented with the binding of var to v.

If the match of apat against v fails or diverges, then so does the overall match. Aside from the obvious static type constraints for example, it is a static error to match a character against a boolean , the following static class constraints hold: An integer literal pattern can only be matched against a value in the class Num.

A floating literal pattern can only be matched against a value in the class Fractional. These patterns may be removed or changed in future versions of Haskell. It is sometimes helpful to distinguish two kinds of patterns. The irrefutable patterns are as follows: a variable, a wildcard, N apat where N is a constructor defined by newtype and apat is irrefutable see Section 4.

All other patterns are refutable. These examples demonstrate refutable vs.

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It constitutes a specification for the Prelude. Many of the definitions are written with clarity rather than efficiency in mind, and it is not required that the specification be implemented as shown here. The default method definitions, given with class declarations, constitute a specification only of the default method. They do not constitute a specification of the meaning of the method in all instances. To take one particular example, the default method for enumFrom in class Enum will not work properly for types whose range exceeds that of Int because fromEnum cannot map all values in the type to distinct Int values.

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haskell98-report

All patterns must be linear no variable may appear more than once. It is as if an identifier not used elsewhere were put in its place. Attempting to match a pattern can have one of three results: it may fail; it may succeed, returning a binding for each variable in the pattern; or it may diverge i. Pattern matching proceeds from left to right, and outside to inside, according to the following rules: Matching the pattern var against a value v always succeeds and binds var to v. Binding does not imply evaluation. At that point the entire pattern is matched against the value, and if the match fails or diverges, so does the overall computation.

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HASKELL98 REPORT PDF

Gozragore Pages using deprecated image syntax All articles with unsourced statements Articles with unsourced statements from February Articles containing potentially dated statements from May All articles containing potentially dated statements Articles with unsourced statements from April Articles with inconsistent citation formats Wikipedia articles with BNE identifiers Wikipedia articles with BNF identifiers Wikipedia articles with GND identifiers Wikipedia articles with LCCN identifiers Use dmy dates from March Articles with example Haskell code. The committee expressly welcomed creating extensions and variants of Haskell 98 via adding and incorporating experimental features. The main events are:. Monads are a general framework that can model different kinds of computation, including error handling, nondeterminismparsing and software transactional memory.

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Haskell 98 Language and Libraries

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