379 search results for "function"

The Compiler Backend: Bytecode and Native code

The Impact of Polymorphic Comparison

the location of the minor heap in the %r15 register since it's so frequently referenced in OCaml functions. The minor heap pointer can also be changed by [...] hed on the stack (the %rsp register), and a C function call is invoked by placing a pointer to caml_greaterthan in %rax and jumping to caml_c_call

A Tour of OCaml

Side-Effects and the unit Type

Input-output is an example of something taking place when executing a function but which does not appear in the function type. This is called a side-effect and does not stop at I/O. The unit type is often used to ind

Your First OCaml Program

Why Isn't There a Main Function?

ll those will take place in the same order. That's OCaml main. Although bin/main.ml 's name suggests it contains the application entry point into the project, it does not contain a dedicated main function, and there is no requirement that a project must contain a file with that name in order to produce an executable. A compiled OCaml file behaves as though that file were entered line by line into the

OCaml Programming Guidelines

Style dangers

ls that the mutable keyword in the record-type definitions should be implicit. The “too much functional” danger : The programmer that adheres to this [...] systematic rewriting for loops with recursive functions, using lists in contexts where imperative data structures seem to be mandatory to anyone, pass

OCaml Programming Guidelines

OCaml code generally considered unreadable

atically code sequences with let in bindings. Mix computations and side effects, particularly in function calls. Recall that the evaluation order of function call arguments is unspecified, which implies that you must not mix side effects and computation

Profiling

Tail Recursion

then print the string, and jump back, and so on forever. It's a simple loop, not a recursive function call, so it doesn't use any stack space. Here is the assembler for just the loop function defined above: The file is called tail.ml , so following OCaml's usual procedure for naming

Profiling

The Representation of Integers, Tag Bits, Heap-Allocated Values

le_tag: Compare two floats. etc. It uses the following decision tree: Remember our polymorphic > function which caused us so much trouble in the previous [...] and found out that OCaml compiles a call to a C function called greaterthan whenever it sees the polymorphic form of >. This

Formatting and Wrapping Text

Most General Pretty-Printing: Using fprintf

ng fprintf , the lambda-terms printing routines can be written as follows: We use the fprintf function to write the most versatile version of the pretty-printing functions for lambda-terms. Now, the

Modules

Abstract and Read-Only Types

le to access a read-only record field's value, but creating such a record requires using a provided function. The type dalet is read-only . Pattern matchi [...] ut values can only be constructed by the provided functions, here dalet_of . Type gimel is abstract . Values can be created or manipulated, but only as

Loops and Recursions

Mutable Records, References (Again!) and Arrays

OCaml won't let you: Anyway, let's see print_name in action: Notice a strange (and very non-functional) feature of print_name : it modifies its access_count parameter. This function is not "pure." OCaml is a

Sequences

Introduction

In OCaml, any value a of type t can be turned into a constant function by writing fun _ -> a or fun () -> a . The latter function is called a thunk . Using this terminology, Seq.t values are thunks. This explains why sequen

Sequences

Filtering a Sequence

s input incrementally. Unlike traditional recursion, which works towards a base case, corecursive functions must indefinitely produce values as a stream. The trial_div function is corecursive because it does not immediately compute the complete sequence of primes. Instead,

Sequences

Unfolding Sequences

The function Seq.uncons returns the head and tail of a seque [...] ise, it returns None . We can check our map function by applying a square

Lists

List Scanning

has evolved into its present state: pieces of frequently-used code are turned into useful general functions. This is rather clumsy, though. The standard library provides two useful functions for_all and exists for this common problem: There are more elaborate scanning

Memoization

Just for Fun: Party Optimization

We could memoize all calls, but that wouldn't improve speed much.) This requires just introducing a function `lb_mem` that looks up and records memoized forma [...] h the naive recursive implementation called the function party many times with the same arguments. Memoization saves all those calls. Further, the party o

The Compiler Backend: Bytecode and Native code

Understanding Name Mangling

Anonymous functions are hard to predict without inspecting intermedi [...] odify the source code to let-bind the anonymous function to a variable name. The symbol is prefixed by caml and the local module name, with dots replac

A Tour of OCaml

Modules and the Standard Library

f the OCaml module system. It provides a means to separate concerns by preventing name clashes. Two functions having different type may have the same name if [...] provided by different modules. The List.map function which was used earlier in this section is also part of a module, the List module. When the optio

Higher Order Functions

Iterating over Optionals and Results

defined in the standard library. We can do this by pattern-matching on our value and calling our function over the inner value in the Some or Ok branch. A [...] nal and result values. Normally, we want to run a function only if the option has Some value in it or if there is an Ok value . If there is no value in it,

Higher Order Functions

Iterating over custom data types

Again, we iterate by pattern matching on values, applying a function to the deconstructed value and recursing over the [...] we go along: Now before we define our iteration function, its important to define what iteration means for our data type. Do we want to iterate from the bot

Higher Order Functions

Mapping Lists

ct it. The main difference is that instead of throwing away the resulting value from running our function over the elements, we will reconstruct a list f [...] attern match on a list, get the head of it, run a function over it, and recurse over the body.

OCaml Programming Guidelines

When to use open modules rather than leaving them closed

l to open a module that modifies the environment and brings other versions of an important set of functions. For example, the Format module automaticall [...] rinting. This module redefines the usual printing functions print_string , print_int , print_float , etc., so when you use Format , open it systematical

Calling Fortran Libraries

Step 4: Now to OCaml

And voila, we've called the fortran function from OCaml. prompt> ocamlc -o test gtd6.cmo wrap [...] rn how to do it). This tells OCaml that the temp function takes 5 parameters and returns a single floating point and calls the C

Command-line Arguments

Using the Arg Module

The Arg module has many more actions than just Set and Set_string , and some lower-level function for parsing more complicated command lines. He [...] e , giving it our specification list, anonymous function, and usage message. Once it returns, the references will be filled with all the information requi

Maps

Merging Maps

ond map drop drops both entries in the result map Here are examples of duplicate key resolution functions: Note : As with all the other functions of Map , the input maps are not modified. To merge two maps, use the union

Options

Map Over an Option

Incrementing an Integer The following are a few simple examples demonstrating how the Option.map function works with different types and transformations: Our custom map function is the same as the standard library's Option.map : Using pattern matching, it is possible to de

Options

Extract the Content of an Option

lue for Safe Extraction Since the option is None , it returns the provided default value. The function returns "hello" because the option contains a v [...] o value, Option.get raises an exception. The function successfully retrieves the value inside Some 42 . Example 1 : Extracting a Value with Option.g

Basic Data Types and Pattern Matching

Unit

The function print_endline prints the string followed by a l [...] ar with your own text and press Return . The function read_line reads an end-of-line terminated sequence of characters from standard input and returns

Basic Data Types and Pattern Matching

A Complete Example: Mathematical Expressions

The factorise function above introduces another feature: guards to eac [...] e expressions' form, but they call the distrib function recursively on their subexpressions. This ensures that all its subexpressions get multiplied out

Sequences

Taking Parts of a Sequence

his can be used to print integers without looping forever, as shown previously: When executed, the function begins by unfreezing seq (that is, calling seq [...] hing. It is a partial application and returns a function needing a unit to produce a result. a sequence called seq a unit value Observe the first line

Sequences

Understanding the Difference

emains a mystery, take a moment to compare the inputs to the Seq.Cons constructor and Seq.cons function. They look deceptively similar, but one takes a [...] reason, it is not possible to create a Fibonacci function using Seq.cons . Why is it so? The issue with fibs_v1 lies in the recursive call fibs_v1 n (

Monads

Composition and Monad Laws

nad laws: The monadic compose operator would enable us to compose those two into an identity function without having to write any additional code: R [...] r, imagine that we have increment and decrement functions: As the last line suggests, compose can be expressed as infix operator written >=> . We ca

Error Handling

Using the option Type for Errors

It tends to be considered good practice nowadays when a function can fail in cases that are not bugs (i.e., not [...] r than throwing an exception. We can try those functions: Using option it is possible to write

Error Handling

Naming Conventions

exceptions. In such a context, the opposite convention is relatively common: the version of the function that raises exceptions is suffixed with _exn . Using the same functions, that would give the specification: This is extracted from the List module of the standard libr

Error Handling

bind as a Binary Operator

en using Result.bind as a binary operator: Writing x >>= f is very close to what is found in functionally tainted programming languages which have me [...] st. Nevertheless, it has some appeal when named functions are used. It looks a bit like good old Unix pipes: It may seem pointless. To make sense,

Mutability and Imperative Control Flow

It Depends: Module State

has the type Hashtbl.t representing mutable data. It also exposes create , clear , and reset functions. The clear and reset functions return unit . This strongly signals the reader that they perform the side-effect of updating the

Mutability and Imperative Control Flow

Bad: Undocumented Side Effects

If you're writing functions with non-obvious side effects, don't shadow existing definitions. Instead, give the function a descriptive name (for instance, Array.copy_with_analytics ) and document the fact that there's a

Maps

Introduction

StringMap , OCaml's toplevel displays the module's signature. Since it contains a large number of functions, the output copied here is shortened for brevi [...] es the keys' type to be used in the maps, and a function for comparing them. OCaml's Standard Library also provides hash tables, another implementation of

Labelled and Optional Arguments

Defining Optional Parameters With Default Values

at -> float -> float = <fun> # let get_ok ?(exn = fun _ -> Invalid_argument "result is Error _") = function | Ok v -> v | Error e -> raise (exn e);; [...] optional parameter that defaults to 0. Inside the function, the parameter is named x . In the previous section, we've defined a

Labelled and Optional Arguments

Defining Optional Parameters Without Default Values

exmplain use-case --> When an optional parameter isn't given a default value, its type inside the function is made an option . Here, len appears as ?len:int in the function signature. However, inside the body of the

Loops and Recursions

Recursion Example: Maximum Element in a List

the imperative for-loop solution, and (b) much more closely tied to the problem specification. Functional programmers will tell you that it's because the functional style is at a much higher level than the imperative style, and therefore better and easier. Whe

Arrays

Sorting an Array

It sorts the provided array in place and in ascending order, according to the provided comparison function. Sorting performed by Array.sort modifies the c [...] numbers created above, we can use: a comparison function an array To sort an array, we can use the Array.sort

Lists

The Standard Library List Module

In the List module documentation, functions which can raise an exception are marked. Such [...] module contains a wide range of useful utility functions, including pre-written versions of many of the

Lists

Maps and Iterators

In addition, we have an imperative analogue to map , called iter . It takes an imperative function of type 'a -> unit and an 'a list and applies the function to each element in turn. A suitable

Memoization

Fibonacci

imperative constructs (specifically, array update), the side effects are not visible outside the function fibm . So from a client's perspective, fibm is functional. There's no need to mention the imperative implementation (i.e., the benign side effects) that

Monads

The Compiler Backend: Bytecode and Native code

Using the Frame Pointer to Get More Accurate Traces

doesn't require adding in explicit probes to the binary, it does need to understand how to unwind function calls so that the kernel can accurately record the function backtrace for every event. Since Linux 3.9 the kernel has had support for using DWARF debug infor

A Tour of OCaml

Values and Functions

What is a Value?

er to avoid runtime type checks in binaries. In OCaml, the compiler removes type information, so it's not available at runtime. In programming theory, this is called subject reduction . Like most functional programming languages, OCaml is an expression-oriented programming language. That means programs are expressions. Actually, almost everything is an expression. In OCaml, statements don't specify

Values and Functions

Global Definitions

is defined globally. This is what happens when writing a definition in UTop: If the expression can be evaluated, it is. Otherwise, the expression is turned into a value as-is. That's the case of function definition. Every value can be named. This is the purpose of the let … = … statement. The name is on the left; the expression is on the right.

Values and Functions

Pattern Matching on Tuples

The List.split function turns a list of pairs into a pair of lists. Here, each resulting list is bound to a name. A common case is tuples. It allows the creation of two names with a single let .