P. Wadler, List comprehensions. Chapter 7 in P. Jones, The implementation of functional programming languages. Prentice Hall, New York, 1987.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....the correctness of structural recursion is undecidable. The restricted structural recursion is defined by the function h 1 . Then it can be understood as the extension of the function h 1 i.e. ext(h 1 ) R ) srec ;h1 ; T 0 (R ) As shown in [BLS94] ext is equivalent to comprehensions [Wad87]. Comprehensions cover different kinds of collections such as indexed structures, arrays, or sets, trees and graphs. The general aggregator, called in [Bee92] pump, can be defined by structural recursion with T = IN . Examples of such operations are sum which starts with 0 and applies for ....

P. Wadler, List comprehensions. Chapter 7 in P. Jones, The implementation of functional programming languages. Prentice Hall, New York, 1987.

....rare occasions, the heuristics we use can be defeated and the size of the automaton gets very large In fact, as shown in the appendix, some set of clauses defeat any heuristic Other compilers producing treelike pattern matching automata, such as SML NJ or CAML [11] face the same problem. In [1, 10] an alternative technique of compilation is presented: pattern matching expressions are compiled using a backtracking construct. This technique leads to matching automata whose size is linear in the size of the input program. A similar approach may be possible in our case, but it would probably ....

P. Wadler, chapter on the compilation of pattern matching in: S. L. Peyton Jones, "The Implementation of Functional Programming Languages". Prentice-Hall, 1987.

....the correctness of structural recursion is undecidable. The restricted structural recursion is defined by the function h 1 . Then it can be understood as the extension of the function h 1 i.e. ext(h 1 ) R t ) srec ;h1 ; T 0 (R t ) As shown in [BLS94] ext is equivalent to comprehensions [Wad87]. Comprehensions cover different kinds of collections such as indexed structures, arrays, or sets, trees and graphs. The general aggregator, called in [Bee92] pump, can be defined by structural recursion with T 0 = IN . Examples of such operations are sum which starts with 0 and applies for ....

P. Wadler, List comprehensions. Chapter 7 in P. Jones, The implementation of functional programming languages. Prentice Hall, New York, 1987.

....We can even allow a programmer to define new kinds of collection, which will be automatically be equipped with their own query notation. 3.1 Comprehensions For brevity, comprehension (or ZF) notation is not formally described here, merely illustrated by example. A full description is given in [20]. A set comprehension describing the set of squares of all the odd numbers in a set s is conventionally written: fsquare x j x 2 s odd xg We shall use the following notation: square x j x s; odd x] set The notation generalises to comprehensions over arbitrary collections. For example, if l ....

....with the DBPL. In [16] it was argued that comprehensions meet these requirements. The essence of the argument is as follows. Comprehensions are concise because they are a declarative specification of the query. Comprehensions are clear because of their similarity to the relational calculus. In [20] the efficiency of list comprehensions was proved by showing that they perform the minimum number of cons operations required to produce the result list. It remains to be seen whether this is true for comprehensions over all kinds of collection. Comprehensions can be smoothly integrated into a ....

Wadler, P.L. List Comprehensions. Chapter 7 of Peyton Jones, S.L. The Implementation of Functional Programming Languages. Prentice Hall, 1987.

....Section 5 shows how comprehensions can be defined over several bulk types. Section 6 concludes. 2 List Comprehensions This section informally introduces list comprehension, or ZF, notation. A formal semantics of ringad comprehensions is given in Section 5 and a full description can be found in [29]. In mathematics a set comprehension describing the set of squares of all the odd numbers in a set A can be written fsquare x j x 2 A odd xg and has a corresponding list comprehension [square x j x A; odd x] This can be read as the list of squares of x such that x is drawn from A and x is ....

....For example, if is list concatenation, the calculus query f(t) j (t) 2 R (t) 2 Sg corresponds to the comprehension [ t) j (t) R S] 3. 3 Efficiency A list comprehensions is efficient in the sense that it performs the minimum number of cons operations required to produce the result list [29]. Proofs of the efficiency of comprehensions over bulk types other than lists have not yet been attempted, but the lambda calculus semantics of comprehensions makes proof or disproof possible. Pragmatic evidence for the efficiency of list processing is given by commercial products that use it, for ....

Wadler P.L. List Comprehensions. Chapter 7 of Peyton Jones S.L. The Implementation of Functional Programming Languages. Prentice Hall, 1987.

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P. Wadler, chapter on the compilation of pattern matching in: S. L. Peyton Jones, "The Implementation of Functional Programming Languages". Prentice-Hall, 1987.

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