Write a recursive function to reverse a list

The trick is to pick a midpoint near the center of the array, compare the data at that point with the data being searched and then responding to one of three possible conditions:

Write a recursive function to reverse a list

When this value is evaluated, the semantics of Haskell no longer yield a meaningful value. In other words, further operations on the value cannot be defined in Haskell.

Several ways exist to express bottoms in Haskell code. For instance, undefined is an easily called example of a bottom value. This function has type a but lacks any type constraints in its type signature.

Thus, undefined is able to stand in for any type in a function body, allowing type checking to succeed, even if the function is incomplete or lacking a definition entirely. The undefined function is extremely practical for debugging or to accommodate writing incomplete programs.

Another example of a bottom value comes from the evaluation of the error function, which takes a String and returns something that can be of any type. This property is quite similar to undefined, which also can also stand in for any type. Calling error in a function causes the compiler to throw an exception, halt the program, and print the specified error message.

In the divByY function below, passing the function 0 as the divisor results in this function results in such an exception.

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These bottoms exist because the operations cannot be defined in native Haskell. Such operations are baked into the compiler at a very low level. However, this module exists so that Haddock can generate documentation for these primitive operations, while the looping syntax serves as a placeholder for the actual implementation of the primops.

Perhaps the most common introduction to bottoms is writing a partial function that does not have exhaustive pattern matching defined.

C++ - Recursive Reverse Single Linked List - Stack Overflow

For example, the following code has non-exhaustive pattern matching because the case expression, lacks a definition of what to do with a B: The compiler inserts an exception to account for the non-exhaustive patterns: A similar situation can arise with records.

Although constructing a record with missing fields is rarely useful, it is still possible. Bottoms are used extensively throughout the Preludealthough this fact may not be immediately apparent. The reasons for including bottoms are either practical or historical. This function could not be well-typed without the bottom.

Err import Prelude hiding head,!! The preferred method for handling exceptions is to combine the use of safe variants provided in Data. Maybe with the usual fold functions maybe and either.

Another method is to use pattern matching, as shown in listToMaybe, a safer version of head described below: Invoking a bottom defined in terms of error typically will not generate any position information.

However, assert, which is used to provide assertions, can be short-circuited to generate position information in the place of either undefined or error calls. Avoiding Partial Functions Exhaustiveness Pattern matching in Haskell allows for the possibility of non-exhaustive patterns.

For example, passing Nothing to unsafe will cause the program to crash at runtime.

write a recursive function to reverse a list

However, this function is an otherwise valid, type-checked program. Nothing and Just a. Since the case of a Nothing was not defined in unsafe, we say that the pattern matching within that function is non-exhaustive. In other words, the function does not implement appropriate handling of all valid inputs.

Instead of yielding a value, such a function will halt from an incomplete match.


Partial functions from non-exhaustively are a controversial subject, and frequent use of non-exhaustive patterns is considered a dangerous code smell. However, the complete removal of non-exhaustive patterns from the language would itself be too restrictive and forbid too many valid programs.Program Development Using Erlang - Programming Rules and Conventions Abstract.

This is a description of programming rules and advise for how to write systems using Erlang. Preparing Preparing and Running Make. To prepare to use make, you must write a file called the makefile that describes the relationships among files in your program and provides commands for updating each file.

In a program, typically, the executable file is updated from object files, which are in turn made by compiling source files. Given a linked list, print reverse of it using a recursive function.

For example, if the given linked list is 1->2->3->4, then output should be 4->3->2->1. Note that the question is only about printing the reverse. This is pretty nifty. I was working on a problem recently where I had to write a recursive query in which any member could be the root node.

It was a bit wobbly, and I (almost) wish I still had it in front of me to revisit with some of this. Write a program to get distinct word list from the given file.

Write a program to get a line with max word count from the given file. Write a program to convert string to . The following code works fine when head is sent as a parameter to it. As I am new to C, I couldn't understand how it works. Help me out please.

What I Wish I Knew When Learning Haskell ( Stephen Diehl )