Parse numbers

lib/chervil.rb

@@ -1,3 +1,5 @@
+require 'chervil/ast'
 require 'chervil/lexer'
+require 'chervil/parser'
 require 'chervil/token'
 require 'chervil/version'

lib/chervil/ast.rb

@@ -0,0 +1,3 @@
+module Chervil::AST
+  require "chervil/ast/number"
+end

lib/chervil/ast/number.rb

@@ -0,0 +1,13 @@
+module Chervil::AST
+  class Number
+    attr_reader :value
+
+    def initialize(value)
+      @value = value
+    end
+
+    def ==(other)
+      @value == other.value
+    end
+  end
+end

lib/chervil/parser.rb

@@ -0,0 +1,40 @@
+module Chervil
+  class Parser
+    def initialize(lexer)
+      @lexer = lexer
+      @tree = Array.new
+      @current_token = @lexer.get_next_token
+    end
+
+    def parse
+      until @current_token.type == :eof
+        @tree << expr
+      end
+      @tree
+    end
+
+    def expr
+      if @current_token.type == :number
+        constant
+      end
+    end
+
+    def constant
+      case @current_token.type
+      when :number
+        token = eat(:number)
+        AST::Number.new(token.value.to_f)
+      end
+    end
+
+    def eat(type)
+      if @current_token.type == type
+        token = @current_token
+        @current_token = @lexer.get_next_token
+        token
+      else
+        raise "Expected #{type} but got #{@current_token.type}"
+      end
+    end
+  end
+end

spec/parser_spec.rb

@@ -0,0 +1,13 @@
+module Chervil
+  RSpec.describe Parser do
+    def parse(source)
+      lexer = Lexer.new(source)
+      parser = Parser.new(lexer)
+      parser.parse
+    end
+
+    it 'parses a number' do
+      expect(parse("1").first).to eq(AST::Number.new(1.0))
+    end
+  end
+end