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require "./parcom/*"
module Parcom
VERSION = "0.1.0"
# A ParserFail exception should be raised by `Parser#parse` when
# a parse attempt is unsuccessful.
# Raising this exception in the `#parse` method of a Parser "Foo"
# usually follows this pattern to allow for error tracing:
#
# ```
# class Foo(T, V) < Parser(T, V)
# def parse(tokens : Tokens(T)) : Result(T, V)
# helper.parse(tokens)
# rescue ex : ParserFail
# raise ParserFail.new("Foo: #{ex.message}")
# end
# ```
class ParserFail < Exception
end
# `Tokens` is an `Array` wrapper struct to store the input
# stream of one or more `Parser` objects.
# A `Tokens` can be created from any `Iterable`, along with
# `String` objects using a special constructor.
struct Tokens(T)
getter tokens
# Constructs a `Tokens(Char)` from a `String`.
def self.from_string(s : String) : Tokens(Char)
Tokens.new(s.chars)
end
# Constructs a `Tokens` from an `Iterable`.
def initialize(ts : Iterable(T))
if ts.responds_to?(:to_a)
@tokens = ts.to_a
else
@tokens = [] of T
ts.each { |t| @tokens << t }
end
end
# Exposes `Array#[](Int)`.
def [](index : Int) : T
@tokens[index]
end
# Exposes `Array#[](Int, Int)`, but wraps the returned array in a new `Tokens`.
def [](start : Int, count : Int) : Tokens(T)
Tokens.new(@tokens[start, count])
end
# Exposes `Array#[](Range)`, but wraps the returned array in a new `Tokens`.
def [](range : Range) : Tokens(T)
Tokens.new(@tokens[range])
end
# Like `#[]`, but returns `nil` instead of raising an `IndexError`.
def []?(*args)
self.[](*args)
rescue IndexError
nil
end
# Exposes `Array#empty?`.
def empty? : Bool
@tokens.empty?
end
end
# A `Result` stores a `Tokens` object and a parsed value,
# and is effectively used to store the state of a parser chain.
# This is used instead of a `Tuple` or `NamedTuple` because:
# 1. This is more idiomatic than a `Tuple`.
# 2. Crystal does not support generic named tuples.
struct Result(T, V)
getter tokens, value
def initialize(@tokens : Tokens(T), @value : V)
end
end
class AtMost(T, V) < Parser(T, Array(V))
@p : Map(T, Array(V?), Array(V))
def initialize(i : Int, p : Parser(T, V))
@p = Exactly.new(i, Optional.new(p)).map(&.compact)
end
def parse(tokens : Tokens(T)) : Result(T, Array(V))
@p.parse(tokens)
rescue ex : ParserFail
raise ParserFail.new("AtMost: #{ex.message}")
end
end
class Between(T, V) < Parser(T, Array(V))
@p : Map(T, {Array(V), Array(V)}, Array(V))
def initialize(i : Int, j : Int, p : Parser(T, V))
lower = i < j ? i : j
upper = (i - j).abs
@p = (Exactly.new(lower, p) + AtMost.new(upper, p)).map do |tup|
tup[0] + tup[1]
end
end
def parse(tokens : Tokens(T)) : Result(T, Array(V))
@p.parse(tokens)
rescue ex : ParserFail
raise ParserFail.new("Between: #{ex.message}")
end
end
class FirstOf(T, V) < Parser(T, V)
@p : Parser(T, V)
def initialize(ps : Iterable(Parser(T, V)))
ps_iter = ps.each
p = ps_iter.next
if p.is_a?(Iterator::Stop)
raise ArgumentError.new("FirstOf requires atleast one parser, got none")
end
@p = p
p = ps_iter.next
until p.is_a?(Iterator::Stop)
@p = @p | p
p = ps_iter.next
end
end
def parse(tokens : Tokens(T)) : Result(T, V)
@p.parse(tokens)
rescue ex : ParserFail
raise ParserFail.new("FirstOf: #{ex.message}")
end
end
class SepBy(T, V, U) < Parser(T, Array(V))
@p : Map(T, {V, Array(V)}, Array(V))
def initialize(elem : Parser(T, V), sep : Parser(T, U))
@p = (elem + Many(T, U).new(sep >> elem)).map do |tup|
[tup[0]] + tup[1]
end
end
def parse(tokens : Tokens(T)) : Result(T, Array(V))
@p.parse(tokens)
rescue ex : ParserFail
raise ParserFail.new("SepBy: #{ex.message}")
end
end
end
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