IO
IO is an abstraction representing input/output or other side-effecting computations and operations, often as composable values whose execution is separately controlled.
Learn Haskell by Example
An IO action is a Haskell computation that describes interaction with the external world and may produce input/output effects.
- How it is used
- Separates operating-system interaction from pure program logic while building command-line input and output.
- How deep it goes
- Explains action types, do sequencing, recursion, branching, return, pure boundaries, and IO’s monadic role; defers do notation’s general monad details.
- Examples
- Demonstrates an echo program, uppercase input, a recursive line-numbering interaction, command-line help selection, and GHCi evaluation.
- What you can do after
- Apply it to sequence input and output, combine effects with pure transformations, and stop recursive interactive actions conditionally.
Functional Programming in JavaScript
A monadic abstraction for describing and sequencing input/output or other side-effecting actions as values.
- How it is used
- Encapsulates DOM reads and writes so side effects can participate in composable functional pipelines.
- How deep it goes
- Implements IO with constructor, map, chain, and run, then works through a deferred DOM update.
- Examples
- Uses a student-name DOM element transformed with start case, plus a student lookup pipeline wrapped with liftIO.
- What you can do after
- Build it from scratch as a small JavaScript IO type and defer a DOM update until run.
Functional Programming in Scala, Second Edition
IO is a monadic abstraction that represents effectful computations as values whose execution can be controlled separately from their description.
- How it is used
- Separates external interactions from pure program logic by representing requested effects as IO values.
- How deep it goes
- Develops IO[A] through monadic sequencing, reified control flow, tail-recursive interpretation, and its stack-safety and streaming limits.
- Examples
- Uses contest output, a Fahrenheit-to-Celsius console converter, a factorial REPL, and file conversion to demonstrate IO.
- What you can do after
- Build it from scratch as a delayed, monadic, stack-safe description of console and other external operations.
Read how Functional Programming in Scala, Second Edition explains IO →
Julia as a Second Language
IO is Julia's abstract supertype for values that provide input and output operations.
- How it is used
- Provides a common input-and-output interface for files, text buffers, processes, sockets, and terminal output.
- How deep it goes
- Defines the abstract type and works through reading, writing, closing, and a method limitation without implementing concrete IO subtypes.
- Examples
- Uses pizza-sales CSV output, rocket-engine CSV reading and writing, grep process output, and a netcat socket exchange.
- What you can do after
- Apply it via Julia Base functions to read or write through an appropriate IO object and close it when finished.
The Well-Grounded Rubyist, Fourth Edition
An I/O object is a Ruby object that represents an input or output stream and provides operations for transferring data.
- How it is used
- Represents input and output streams as objects for interacting with files, keyboards, screens, and other devices.
- How deep it goes
- Explains stream objects, common output methods, enumeration, record separators, and file modes without detailing system-call internals.
- Examples
- Demonstrates writing to STDERR, iterating over STDIN lines, and writing then appending data to a file.
- What you can do after
- Operate on streams using output methods, enumerate input records, and write or append data through File objects.
Read how The Well-Grounded Rubyist, Fourth Edition explains IO →
Functional Design and Architecture: Examples in Haskell
IO is the Haskell type constructor for computations that may perform input, output, or other external effects.
- How it is used
- Separates pure calculations from external effects and confines those effects to an explicit call chain.
- How deep it goes
- Explains effect propagation and demonstrates a complete program, but does not detail IO runtime implementation.
- Examples
- Uses max, printNumber, printMaxNumber, main, and concurrent state-management structures.
- What you can do after
- Evaluate which functions perform effects and organize effectful or concurrent behavior behind explicit boundaries.
Read how Functional Design and Architecture: Examples in Haskell explains IO →
Related concepts
- read methodused by · A read method obtains data from an input source, typically returning it or delivering it to a consumer.
- abstract typekind of · An abstract type defines a conceptual interface or classification without directly representing concrete instances or necessarily being instantiated.
- file objectincludes · A file object is a program-accessible representation of an open file or stream, including its access state and input/output operations.
- putsuses · An output operation that writes data to an I/O stream and normally appends a newline.
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