Full namespace name: clojure.algo.monads

Project home page is http://github.com/clojure/algo.monads/

This library contains the most commonly used monads as well as macros for defining and using monads and useful monadic functions.See also: Monad tutorial part 1 Monad tutorial part 2 Monad tutorial part 3 Monad tutorial part 4 Blog posts on monads in Clojure

Accumulation of values into containersKnown implementations: clojure.lang.APersistentSet, clojure.lang.IPersistentList, clojure.lang.IPersistentVector, java.lang.String

Usage: (writer-m-add container value)

add value to container, return new container

Usage: (writer-m-combine container1 container2)

combine two containers, return new container

Usage: (call-cc f)

A computation in the cont monad that calls function f with a single argument representing the current continuation. The function f should return a continuation (which becomes the return value of call-cc), or call the passed-in current continuation to terminate.Source

Usage: (cond-statement expr mexpr continuation)

Process a :cond steps when adding a new monadic step to the mexpr.Source

Monad describing computations in continuation-passing style. The monadic values are functions that are called with a single argument representing the continuation of the computation, to which they pass their result.Source

Usage: (defmonad name doc-string operations) (defmonad name operations)

Define a named monad by defining the monad operations. The definitions are written like bindings to the monad operations m-bind and m-result (required) and m-zero and m-plus (optional).Source

Usage: (defmonadfn name docstring? attr-map? args expr) (defmonadfn name docstring? attr-map? (args expr) ...)

Like defn, but for functions that use monad operations and are used inside a with-monad block.Source

Usage: (domonad steps expr) (domonad name steps expr)

Monad comprehension. Takes the name of a monad, a vector of steps given as binding-form/monadic-expression pairs, and a result value specified by expr. The monadic-expression terms can use the binding variables of the previous steps. If the monad contains a definition of m-zero, the step list can also contain conditions of the form :when p, where the predicate p can contain the binding variables from all previous steps. A clause of the form :let [binding-form expr ...], where the bindings are given as a vector as for the use in let, establishes additional bindings that can be used in the following steps.Source

Usage: (fetch-state)

Return a state-monad function that returns the current state and does not modify it.Source

Usage: (fetch-val key)

Return a state-monad function that assumes the state to be a map and returns the value corresponding to the given key. The state is not modified.Source

Monad describing plain computations. This monad does in fact nothing at all. It is useful for testing, for combination with monad transformers, and for code that is parameterized with a monad.Source

Usage: (local f g)

Runs reader g in the context of an environment modified by fSource

Chains together monadic computation steps that are each functions of one parameter. Each step is called with the result of the previous step as its argument. (m-chain (step1 step2)) is equivalent to (fn [x] (domonad [r1 (step1 x) r2 (step2 r1)] r2)).Source

Converts a monadic value containing a monadic value into a 'simple' monadic value.Source

Usage: (m-lift n f)

Converts a function f of n arguments into a function of n monadic arguments returning a monadic value.Source

'Executes' the sequence of monadic values resulting from mapping f onto the values xs. f must return a monadic value.Source

Return the reduction of (m-lift 2 f) over the list of monadic values mvs with initial value (m-result val).Source

'Executes' the monadic values in ms and returns a sequence of the basic values contained in them.Source

While (p x) is false, replace x by the value returned by the monadic computation (f x). Return (m-result x) for the first x for which (p x) is true.Source

Usage: (m-when test m-expr)

If test is logical true, return monadic value m-expr, else return (m-result nil).Source

Usage: (m-when-not test m-expr)

If test if logical false, return monadic value m-expr, else return (m-result nil).Source

Monad describing computations with possible failures. Failure is represented by nil, any other value is considered valid. As soon as a step returns nil, the whole computation will yield nil as well.Source

Usage: (maybe-t m) (maybe-t m nothing) (maybe-t m nothing which-m-plus)

Monad transformer that transforms a monad m into a monad in which the base values can be invalid (represented by nothing, which defaults to nil). The third argument chooses if m-zero and m-plus are inherited from the base monad (use :m-plus-from-base) or adopt maybe-like behaviour (use :m-plus-from-transformer). The default is :m-plus-from-base if the base monad m has a definition for m-plus, and :m-plus-from-transformer otherwise.Source

Usage: (monad operations)

Define a monad by defining the monad operations. The definitions are written like bindings to the monad operations m-bind and m-result (required) and m-zero and m-plus (optional).Source

Usage: (monad-transformer base which-m-plus operations)

Define a monad transformer in terms of the monad operations and the base monad. The argument which-m-plus chooses if m-zero and m-plus are taken from the base monad or from the transformer.Source

Monad describing computations which read values from a shared environment. Also known as the environment monad.Source

Usage: (run-cont c)

Execute the computation c in the cont monad and return its result.Source

Monad describing multi-valued computations, i.e. computations that can yield multiple values. Any object implementing the seq protocol can be used as a monadic value.Source

Usage: (sequence-t m) (sequence-t m which-m-plus)

Monad transformer that transforms a monad m into a monad in which the base values are sequences. The argument which-m-plus chooses if m-zero and m-plus are inherited from the base monad (use :m-plus-from-base) or adopt sequence-like behaviour (use :m-plus-from-transformer). The default is :m-plus-from-base if the base monad m has a definition for m-plus, and :m-plus-from-transformer otherwise.Source

Monad describing multi-valued computations, like sequence-m, but returning sets of results instead of sequences of results.Source

Usage: (set-state s)

Return a state-monad function that replaces the current state by s and returns the previous state.Source

Usage: (set-val key val)

Return a state-monad function that assumes the state to be a map and replaces the value associated with key by val. The old value is returned.Source

Monad describing stateful computations. The monadic values have the structure (fn [old-state] [result new-state]).Source

Usage: (state-m-until p f x)

An optimized implementation of m-until for the state monad that replaces recursion by a loop.Source

Usage: (state-t m)

Monad transformer that transforms a monad m into a monad of stateful computations that have the base monad type as their result.Source

Usage: (update-state f)

Return a state-monad function that replaces the current state by the result of f applied to the current state and that returns the old state.Source

Usage: (update-val key f)

Return a state-monad function that assumes the state to be a map and replaces the value associated with the given key by the return value of f applied to the old value. The old value is returned.Source

Usage: (with-monad monad & exprs)

Evaluates an expression after replacing the keywords defining the monad operations by the functions associated with these keywords in the monad definition given by name.Source

Usage: (with-state-field key statement)

Returns a state-monad function that expects a map as its state and runs statement (another state-monad function) on the state defined by the map entry corresponding to key. The map entry is updated with the new state returned by statement.Source

Usage: (writer-m empty-accumulator)

Monad describing computations that accumulate data on the side, e.g. for logging. The monadic values have the structure [value log]. Any of the accumulators from clojure.contrib.accumulators can be used for storing the log data. Its empty value is passed as a parameter.Source

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