chain

parsley.expr.chain$

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.

Attributes

Since:: 2.2.0
Source:: chain.scala
Graph
Supertypes: class Object
trait Matchable
class Any
Self type: chain.type

Members list

Concise view

Unary Operator Chains

These chains allow for the chaining together and application of multiple prefix or postfix unary operators to a single value.

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 ops. The result of p, x, is applied to each of the results of the ops, f1 through fn, such that f1 is applied first and fn last: fn(fn-1(..f1(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.

Attributes

op

the postfix operator to repeatedly parser after p.

p

the single value to be parsed.

Returns:

a parser that an initial p, then many ops, and applies all of the results left-associatively.

Since:

2.2.0

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("++") #> Inc <|> string("--") #> 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(..)

Source:

chain.scala

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 ops. The result of p, x, is applied to each of the results of the ops, f1 through fn, such that f1 is applied first and fn last: fn(fn-1(..f1(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.

Attributes

op

the postfix operator to repeatedly parser after p.

p

the single value to be parsed.

Returns:

a parser that an initial p, then some ops, and applies all of the results left-associatively.

Since:

3.0.0

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("++") #> Inc <|> string("--") #> 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(..)

Source:

chain.scala

This combinator handles right-assocative parsing, and application of, zero or more prefix unary operators to a single value.

First parse many repeated ops. When there are no more ops left to parse, parse a single p. The result of p, x, is applied to each of the results of the ops, f1 through fn, such that fn is applied first and f1 last: f1(f2(..fn(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.

Attributes

op

the prefix operator to repeatedly parse before p.

p

the single value to be parsed.

Returns:

a parser that parses many ops, and a final p, and applies all of the results right-associatively.

Since:

2.2.0

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('-') #> Negate <|> char('+') #> 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(..)

Source:

chain.scala

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 ops. When there are no more ops left to parse, parse a single p. The result of p, x, is applied to each of the results of the ops, f1 through fn, such that fn is applied first and f1 last: f1(f2(..fn(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.

Attributes

op

the prefix operator to repeatedly parse before p.

p

the single value to be parsed.

Returns:

a parser that parses some ops, and a final p, and applies all of the results right-associatively.

Since:

3.0.0

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('-') #> Negate <|> char('+') #> 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(..)

Source:

chain.scala

Binary Operator Chains

These chains allow for the chaining together of values and binary operators in either left- or right-associative application.

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 ps, x1 through xn, are combined with the results of the ops, f1 through fn-1, with left-associative application: fn-1(fn-2(..f1(x1, x2).., xn-1), xn). 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.

Attributes

op

the operator between each value.

p

the value to be parsed.

x

the default value to return if no ps can be parsed.

Returns:

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 also:

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

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('+') #> 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))

Source:

chain.scala

This combinator handles left-associative parsing, and application of, zero or more binary operators between one or more values.

Attributes

op

the operator between each value.

p

the value to be parsed.

Returns:

a parser that parses alternating p and op, ending in a p and applies their results left-associatively.

See also:

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

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('+') #> 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(..)

Source:

chain.scala

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 ps, x1 through xn, are combined with the results of the ops, f1 through fn-1, with right-associative application: f1(x1, f2(x2, ..fn-1(xn-1, xn)..)). 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.

Attributes

op

the operator between each value.

p

the value to be parsed.

x

the default value to return if no ps can be parsed.

Returns:

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 also:

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

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('+') #> 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))

Source:

chain.scala

This combinator handles right-associative parsing, and application of, zero or more binary operators between one or more values.

Attributes

op

the operator between each value.

p

the value to be parsed.

Returns:

a parser that parses alternating p and op, ending in a p and applies their results right-associatively.

See also:

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

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('+') #> 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(..)

Source:

chain.scala

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