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chain.scala
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chain.scala
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/*
* Copyright 2020 Parsley Contributors <https://github.com/j-mie6/Parsley/graphs/contributors>
*
* SPDX-License-Identifier: BSD-3-Clause
*/
package parsley.expr
import parsley.Parsley
import parsley.internal.deepembedding.frontend
/** This module contains the very useful chaining family of combinators,
* which are mostly used to parse operators and expressions of varying fixities.
* It is a more low-level API compared with [[precedence]].
* @since 2.2.0
* @group Chains
*
* @groupprio binary 0
* @groupname binary Binary Operator Chains
* @groupdesc binary
* These chains allow for the chaining together of values and binary operators in either left- or right-associative application.
*
* @groupprio unary 0
* @groupname unary Unary Operator Chains
* @groupdesc unary
* These chains allow for the chaining together and application of multiple prefix or postfix unary operators to a single value.
*/
object chain {
/** This combinator handles right-associative parsing, and application of, '''zero''' or more binary operators between '''one''' or more values.
*
* First parse `p`, then parse `op` followed by a `p` repeatedly. The results of the `p`s, `x,,1,,` through `x,,n,,`, are combined with the results
* of the `op`s, `f,,1,,` through `f,,n-1,,`, with right-associative application: `f,,1,,(x,,1,,, f,,2,,(x,,2,,, ..f,,n-1,,(x,,n-1,,, x,,n,,)..))`. This
* application is then returned as the result of the combinator. If `p` or `op` fails having consumed input at any point, the whole combinator fails.
*
* @example {{{
* scala> import parsley.expr.chain
* scala> import parsley.character.{digit, char}
* scala> sealed trait Expr
* scala> case class Add(x: Expr, y: Expr) extends Expr
* scala> case class Num(x: Int) extends Expr
* scala> val expr = chain.right1(digit.map(d => Num(d.asDigit)), char('+').as(Add))
* scala> expr.parse("1+2+3+4")
* val res0 = Success(Add(Num(1), Add(Num(2), Add(Num(3), Num(4)))))
* scala> expr.parse("")
* val res1 = Failure(..)
* }}}
*
* @param p the value to be parsed.
* @param op the operator between each value.
* @return a parser that parses alternating `p` and `op`, ending in a `p` and applies their results right-associatively.
* @see [[infix.right1 `infix.right1`]] for a version where the types can vary, ensuring that the associativity is enforced in a type-safe way.
* @since 4.0.0
* @group binary
*/
def right1[A](p: Parsley[A], op: =>Parsley[(A, A) => A]): Parsley[A] = infix.right1(p, op)
/** This combinator handles left-associative parsing, and application of, '''zero''' or more binary operators between '''one''' or more values.
*
* First parse `p`, then parse `op` followed by a `p` repeatedly. The results of the `p`s, `x,,1,,` through `x,,n,,`, are combined with the results
* of the `op`s, `f,,1,,` through `f,,n-1,,`, with left-associative application: `f,,n-1,,(f,,n-2,,(..f,,1,,(x,,1,,, x,,2,,).., x,,n-1,,), x,,n,,)`. This
* application is then returned as the result of the combinator. If `p` or `op` fails having consumed input at any point, the whole combinator fails.
*
* @example {{{
* scala> import parsley.expr.chain
* scala> import parsley.character.{digit, char}
* scala> sealed trait Expr
* scala> case class Add(x: Expr, y: Expr) extends Expr
* scala> case class Num(x: Int) extends Expr
* scala> val expr = chain.left1(digit.map(d => Num(d.asDigit)), char('+').as(Add))
* scala> expr.parse("1+2+3+4")
* val res0 = Success(Add(Add(Add(Num(1), Num(2)), Num(3)), Num(4)))
* scala> expr.parse("")
* val res1 = Failure(..)
* }}}
*
* @param p the value to be parsed.
* @param op the operator between each value.
* @return a parser that parses alternating `p` and `op`, ending in a `p` and applies their results left-associatively.
* @see [[infix.left1 `infix.left1`]] for a version where the types can vary, ensuring that the associativity is enforced in a type-safe way.
* @since 4.0.0
* @group binary
*/
def left1[A](p: Parsley[A], op: =>Parsley[(A, A) => A]): Parsley[A] = infix.left1(p, op)
/** This combinator handles right-associative parsing, and application of, '''zero''' or more binary operators between '''zero''' or more values.
*
* First parse `p`, then parse `op` followed by a `p` repeatedly. The results of the `p`s, `x,,1,,` through `x,,n,,`, are combined with the results
* of the `op`s, `f,,1,,` through `f,,n-1,,`, with right-associative application: `f,,1,,(x,,1,,, f,,2,,(x,,2,,, ..f,,n-1,,(x,,n-1,,, x,,n,,)..))`. This
* application is then returned as the result of the combinator. If `p` or `op` fails having consumed input at any point, the whole combinator fails.
* If no `p` could be parsed, this combinator will return a default result `x`.
*
* @example {{{
* scala> import parsley.expr.chain
* scala> import parsley.character.{digit, char}
* scala> sealed trait Expr
* scala> case class Add(x: Expr, y: Expr) extends Expr
* scala> case class Num(x: Int) extends Expr
* scala> val expr = chain.right(digit.map(d => Num(d.asDigit)), char('+').as(Add), Num(0))
* scala> expr.parse("1+2+3+4")
* val res0 = Success(Add(Num(1), Add(Num(2), Add(Num(3), Num(4)))))
* scala> expr.parse("")
* val res1 = Success(Num(0))
* }}}
*
* @param p the value to be parsed.
* @param op the operator between each value.
* @param x the default value to return if no `p`s can be parsed.
* @return a parser that parses alternating `p` and `op`, ending in a `p` and applies their results right-associatively or
* returns `x` if no `p` was parsed.
* @see [[infix.right `infix.right`]] for a version where the types can vary, ensuring that the associativity is enforced in a type-safe way.
* @since 4.0.0
* @group binary
*/
def right[A](p: Parsley[A], op: =>Parsley[(A, A) => A], x: A): Parsley[A] = infix.right(p, op, x) // TODO: right(x)(p, op)?
/** This combinator handles left-associative parsing, and application of, '''zero''' or more binary operators between '''zero''' or more values.
*
* First parse `p`, then parse `op` followed by a `p` repeatedly. The results of the `p`s, `x,,1,,` through `x,,n,,`, are combined with the results
* of the `op`s, `f,,1,,` through `f,,n-1,,`, with left-associative application: `f,,n-1,,(f,,n-2,,(..f,,1,,(x,,1,,, x,,2,,).., x,,n-1,,), x,,n,,)`. This
* application is then returned as the result of the combinator. If `p` or `op` fails having consumed input at any point, the whole combinator fails.
* If no `p` could be parsed, this combinator will return a default result `x`.
*
* @example {{{
* scala> import parsley.expr.chain
* scala> import parsley.character.{digit, char}
* scala> sealed trait Expr
* scala> case class Add(x: Expr, y: Expr) extends Expr
* scala> case class Num(x: Int) extends Expr
* scala> val expr = chain.left(digit.map(d => Num(d.asDigit)), char('+').as(Add), Num(0))
* scala> expr.parse("1+2+3+4")
* val res0 = Success(Add(Add(Add(Num(1), Num(2)), Num(3)), Num(4)))
* scala> expr.parse("")
* val res1 = Success(Num(0))
* }}}
*
* @param p the value to be parsed.
* @param op the operator between each value.
* @param x the default value to return if no `p`s can be parsed.
* @return a parser that parses alternating `p` and `op`, ending in a `p` and applies their results left-associatively or
* returns `x` if no `p` was parsed.
* @see [[infix.left `infix.left`]] for a version where the types can vary, ensuring that the associativity is enforced in a type-safe way.
* @since 4.0.0
* @group binary
*/
def left[A](p: Parsley[A], op: =>Parsley[(A, A) => A], x: A): Parsley[A] = infix.left(p, op, x) // TODO: left(x)(p, op)?
/** This combinator handles right-assocative parsing, and application of, '''zero''' or more prefix unary operators to a single value.
*
* First parse many repeated `op`s. When there are no more `op`s left to parse, parse a single `p`. The result of `p`, `x`, is
* applied to each of the results of the `op`s, `f,,1,,` through `f,,n,,`, such that `f,,n,,` is applied first and `f,,1,,` last:
* `f,,1,,(f,,2,,(..f,,n,,(x)..))`. This application is then returned as the result of the combinator. If `p` or `op` fails having
* consumed input at any point, the whole combinator fails.
*
* @example {{{
* scala> import parsley.expr.chain
* scala> import parsley.character.{digit, char}
* scala> sealed trait Expr
* scala> case class Negate(x: Expr) extends Expr
* scala> case class Id(x: Expr) extends Expr
* scala> case class Num(x: Int) extends Expr
* scala> val expr = chain.prefix(char('-').as(Negate) <|> char('+').as(Id), digit.map(d => Num(d.asDigit)))
* scala> expr.parse("--+1")
* val res0 = Success(Negate(Negate(Id(Num(1)))))
* scala> expr.parse("1")
* val res1 = Success(Num(1))
* scala> expr.parse("")
* val res2 = Failure(..)
* }}}
*
* @param op the prefix operator to repeatedly parse before `p`.
* @param p the single value to be parsed.
* @return a parser that parses many `op`s, and a final `p`, and applies all of the results right-associatively.
* @since 2.2.0
* @group unary
*/
def prefix[A](op: Parsley[A => A], p: Parsley[A]): Parsley[A] = new Parsley(new frontend.ChainPre(p.internal, op.internal))
/** This combinator handles left-assocative parsing, and application of, '''zero''' or more postfix unary operators to a single value.
*
* First parse a single `p`. Then, parse many repeated `op`s. The result of `p`, `x`, is
* applied to each of the results of the `op`s, `f,,1,,` through `f,,n,,`, such that `f,,1,,` is applied first and `f,,n,,` last:
* `f,,n,,(f,,n-1,,(..f,,1,,(x)..))`. This application is then returned as the result of the combinator. If `p` or `op` fails having
* consumed input at any point, the whole combinator fails.
*
* @example {{{
* scala> import parsley.expr.chain
* scala> import parsley.character.{digit, string}
* scala> sealed trait Expr
* scala> case class Inc(x: Expr) extends Expr
* scala> case class Dec(x: Expr) extends Expr
* scala> case class Num(x: Int) extends Expr
* scala> val expr = chain.postfix(digit.map(d => Num(d.asDigit)), string("++").as(Inc) <|> string("--").as(Dec))
* scala> expr.parse("1++----")
* val res0 = Success(Dec(Dec(Inc(Num(1)))))
* scala> expr.parse("1")
* val res1 = Success(Num(1))
* scala> expr.parse("")
* val res2 = Failure(..)
* }}}
*
* @param p the single value to be parsed.
* @param op the postfix operator to repeatedly parser after `p`.
* @return a parser that an initial `p`, then many `op`s, and applies all of the results left-associatively.
* @since 2.2.0
* @group unary
*/
def postfix[A](p: Parsley[A], op: =>Parsley[A => A]): Parsley[A] = new Parsley(new frontend.ChainPost(p.internal, op.internal))
/** This combinator handles right-assocative parsing, and application of, '''one''' or more prefix unary operators to a single value.
*
* First parse at least one repeated `op`s. When there are no more `op`s left to parse, parse a single `p`. The result of `p`, `x`, is
* applied to each of the results of the `op`s, `f,,1,,` through `f,,n,,`, such that `f,,n,,` is applied first and `f,,1,,` last:
* `f,,1,,(f,,2,,(..f,,n,,(x)..))`. This application is then returned as the result of the combinator. If `p` or `op` fails having
* consumed input at any point, the whole combinator fails.
*
* @example {{{
* scala> import parsley.expr.chain
* scala> import parsley.character.{digit, char}
* scala> sealed trait Expr
* scala> case class Negate(x: Expr) extends Expr
* scala> case class Id(x: Expr) extends Expr
* scala> case class Num(x: Int) extends Expr
* scala> val expr = chain.prefix1(char('-').as(Negate) <|> char('+').as(Id), digit.map(d => Num(d.asDigit)))
* scala> expr.parse("--+1")
* val res0 = Success(Negate(Negate(Id(Num(1)))))
* scala> expr.parse("1")
* val res1 = Failure(..)
* scala> expr.parse("")
* val res2 = Failure(..)
* }}}
*
* @param op the prefix operator to repeatedly parse before `p`.
* @param p the single value to be parsed.
* @return a parser that parses some `op`s, and a final `p`, and applies all of the results right-associatively.
* @since 3.0.0
* @group unary
*/
def prefix1[A, B <: A](op: Parsley[A => B], p: =>Parsley[A]): Parsley[B] = op <*> prefix(op, p)
/** This combinator handles left-assocative parsing, and application of, '''one''' or more postfix unary operators to a single value.
*
* First parse a single `p`. Then, parse at least one repeated `op`s. The result of `p`, `x`, is
* applied to each of the results of the `op`s, `f,,1,,` through `f,,n,,`, such that `f,,1,,` is applied first and `f,,n,,` last:
* `f,,n,,(f,,n-1,,(..f,,1,,(x)..))`. This application is then returned as the result of the combinator. If `p` or `op` fails having
* consumed input at any point, the whole combinator fails.
*
* @example {{{
* scala> import parsley.expr.chain
* scala> import parsley.character.{digit, string}
* scala> sealed trait Expr
* scala> case class Inc(x: Expr) extends Expr
* scala> case class Dec(x: Expr) extends Expr
* scala> case class Num(x: Int) extends Expr
* scala> val expr = chain.postfix1(digit.map(d => Num(d.asDigit)), string("++").as(Inc) <|> string("--").as(Dec))
* scala> expr.parse("1++----")
* val res0 = Success(Dec(Dec(Inc(Num(1)))))
* scala> expr.parse("1")
* val res1 = Failure(..)
* scala> expr.parse("")
* val res2 = Failure(..)
* }}}
*
* @param p the single value to be parsed.
* @param op the postfix operator to repeatedly parser after `p`.
* @return a parser that an initial `p`, then some `op`s, and applies all of the results left-associatively.
* @since 3.0.0
* @group unary
*/
def postfix1[A, B <: A](p: Parsley[A], op: =>Parsley[A => B]): Parsley[B] = {
lazy val op_ = op
postfix(p <**> op_, op_)
}
}