Add Paco::Combinators.index

CHANGELOG.md

@@ -21,6 +21,16 @@ rescue Paco::ParseError => e
 end
 ```
 
+- `Paco::Combinators.index` method. ([@skryukov])
+
+Call `Paco::Combinators.index` to get `Paco::Index` representing the current offset into the parse without consuming the input.
+`Paco::Index` has a 0-based character offset attribute `:pos` and 1-based `:line` and `:column` attributes.
+
+```ruby
+index.parse("Paco") #=> #<struct Paco::Index pos=0, line=1, column=1> 
+```
+
+
 ### Changed
 
 - `Paco::Combinators.seq_map` merged into `Paco::Combinators.seq`. ([@skryukov])

bin/console

@@ -4,12 +4,7 @@
 require "bundler/setup"
 require "paco"
 
-# You can add fixtures and/or initialization code here to make experimenting
-# with your gem easier. You can also use a different console, if you like.
-
-# (If you use this, don't forget to add pry to your Gemfile!)
-# require "pry"
-# Pry.start
+include Paco
 
 require "irb"
 IRB.start(__FILE__)

docs/paco.md

@@ -234,6 +234,19 @@ example = lazy { failed("always fails") }
 example.parse("Paco") #=> Paco::ParseError
 ```
 
+### Paco::Combinators.index
+
+Returns parser that returns `Paco::Index` representing the current offset into the parse without consuming the input.
+`Paco::Index` has a 0-based character offset attribute `:pos` and 1-based `:line` and `:column` attributes.
+
+```ruby
+include Paco
+
+example = seq(one_of("123\n ").many.join, index, remainder)
+
+example.parse("1\n2\n3\n\n Paco") #=> ["1\n2\n3\n\n ", #<struct Paco::Index pos=8, line=5, column=2>, "Paco"] 
+```
+
 ## Paco::Combinators: Text related methods
 
 ### Paco::Combinators.string(matcher)

lib/paco/combinators.rb

@@ -153,6 +153,13 @@ def optional(parser)
       alt(parser, succeed(nil))
     end
 
+    # Returns parser that returns `Paco::Index` representing
+    # the current offset into the parse without consuming the input.
+    # @return [Paco::Parser]
+    def index
+      Parser.new { |ctx| ctx.index }
+    end
+
     # Helper used for memoization
     def memoize(&block)
       Memoizer.memoize(block.source_location, &block)

lib/paco/context.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require "paco/callstack"
+require "paco/index"
 
 module Paco
   class Context
@@ -25,15 +26,10 @@ def eof?
       pos >= input.length
     end
 
+    # @param [Integer] from
+    # @return [Paco::Index]
     def index(from = nil)
-      from ||= pos
-      lines = input[0..from].lines
-
-      {
-        line: lines.length,
-        column: lines[-1]&.length || 0,
-        pos: from
-      }
+      Index.calculate(input: input, pos: from || pos)
     end
 
     # @param [Paco::Parser] parser

lib/paco/index.rb

@@ -0,0 +1,15 @@
+module Paco
+  Index = Struct.new(:pos, :line, :column) do
+    # @param [String] input
+    # @param [Integer] pos
+    def self.calculate(input:, pos:)
+      raise ArgumentError, "`pos` must be a non-negative integer" if pos < 0
+      raise ArgumentError, "`pos` is grater then input length" if pos > input.length
+
+      lines = input[0..pos].lines
+      line = lines.empty? ? 1 : lines.length
+      column = lines.last&.length || 1
+      new(pos, line, column)
+    end
+  end
+end

lib/paco/parse_error.rb

@@ -20,7 +20,7 @@ def message
       index = ctx.index(pos)
       <<~MSG
         \nParsing error
-        line #{index[:line]}, column #{index[:column]}:
+        line #{index.line}, column #{index.column}:
         unexpected #{ctx.eof? ? "end of file" : ctx.input[pos].inspect}
         expecting #{expected}
       MSG

spec/paco/combinators_spec.rb

@@ -187,4 +187,10 @@
       expect { example.parse("Paco") }.to raise_error(Paco::ParseError)
     end
   end
+
+  describe "#index" do
+    it "returns index" do
+      expect(index.parse("")).to eq(Paco::Index.new(0, 1, 1))
+    end
+  end
 end

spec/paco/index_spec.rb

@@ -0,0 +1,26 @@
+require "spec_helper"
+
+RSpec.describe Paco::Index do
+  subject(:index) { described_class }
+
+  let(:input) { "1\n2\n\n3\nPaco" }
+
+  it "returns index", :aggregate_failures do
+    expect(index.calculate(input: input, pos: 0)).to eq(Paco::Index.new(0, 1, 1))
+    expect(index.calculate(input: input, pos: 1)).to eq(Paco::Index.new(1, 1, 2))
+    expect(index.calculate(input: input, pos: 2)).to eq(Paco::Index.new(2, 2, 1))
+    expect(index.calculate(input: input, pos: 10)).to eq(Paco::Index.new(10, 5, 4))
+  end
+
+  it "returns start position when empty string" do
+    expect(index.calculate(input: "", pos: 0)).to eq(Paco::Index.new(0, 1, 1))
+  end
+
+  it "raises an error when pos < 0" do
+    expect { index.calculate(input: input, pos: -1) }.to raise_error(ArgumentError)
+  end
+
+  it "raises an error when pos > input length" do
+    expect { index.calculate(input: input, pos: 1000) }.to raise_error(ArgumentError)
+  end
+end