4 files changed, 113 insertions, 0 deletions
diff --git a/src/thue/parser.cr b/src/thue/parser.cr
new file mode 100644
index 0000000..6b3907b
--- /dev/null
+++ b/src/thue/parser.cr
@@ -0,0 +1,50 @@
+require "../util.cr"
+require "./thue.cr"
+require "./rule.cr"
+
+class Thue::Parser
+  def initialize(code_io : IO)
+    @raw_code = code_io.gets_to_end
+    code_io.close # just in case
+  end
+
+  def parse
+    rules = [] of Rule
+    line_iterator = @raw_code.lines.each
+
+    line_iterator.each do |line|
+      case line
+      when "", "::="
+        # stops iteration of lines to be picked up by string builder
+        break
+
+      # returned match objects are provably not_nil, safe
+      when .matches?(R_INPUT_RULE)
+        m = line.match(R_INPUT_RULE).not_nil!
+        rules << InputRule.new(m[1])
+
+      when .matches?(R_OUTPUT_RULE)
+        m = line.match(R_OUTPUT_RULE).not_nil!
+        rules << OutputRule.new(m[1], m[2])
+
+      when .matches?(R_NORMAL_RULE)
+        m = line.match(R_NORMAL_RULE).not_nil!
+        rules << NormalRule.new(m[1], m[2])
+
+      else
+        raise Util::ParserError.new("No separator between code and initial state near '#{line}'")
+      end
+    end
+
+    state = String.build do |str|
+      # resumes from where rule parser left off
+      line_iterator.each do |line|
+        str << line
+        str << '\n'
+      end
+    end
+
+    {rules, state}
+  end
+end
+
diff --git a/src/thue/program.cr b/src/thue/program.cr
new file mode 100644
index 0000000..c59780b
--- /dev/null
+++ b/src/thue/program.cr
@@ -0,0 +1,13 @@
+require "./thue.cr"
+require "./parser.cr"
+
+class Thue::Program
+  def initialize(@parser : Parser)
+  end
+
+  def interpret
+    something = @parser.parse
+    puts something
+  end
+end
+
diff --git a/src/thue/rule.cr b/src/thue/rule.cr
new file mode 100644
index 0000000..34c2396
--- /dev/null
+++ b/src/thue/rule.cr
@@ -0,0 +1,43 @@
+require "./thue.cr"
+
+abstract struct Thue::Rule
+  @pattern : Regex
+
+  def initialize(pattern : String)
+    @pattern = Regex.new(pattern)
+  end
+
+  def matches?(str : String) : Bool
+    str.matches?(@pattern)
+  end
+
+  abstract def replacement : String
+end
+
+struct Thue::NormalRule < Thue::Rule
+  def initialize(pattern : String, @replacement : String)
+    super(pattern)
+  end
+
+  def replacement : String
+    @replacement
+  end
+end
+
+struct Thue::InputRule < Thue::Rule
+  def replacement : String
+    gets
+  end
+end
+
+struct Thue::OutputRule < Thue::Rule
+  def initialize(pattern : String, @output : String)
+    super(pattern)
+  end
+
+  def replacement : String
+    print @output
+    return ""
+  end
+end
+
diff --git a/src/thue/thue.cr b/src/thue/thue.cr
new file mode 100644
index 0000000..9c22b96
--- /dev/null
+++ b/src/thue/thue.cr
@@ -0,0 +1,7 @@
+module Thue
+  # Allow matching empty patterns, handle during parsing
+  R_NORMAL_RULE = /^(.*)::=(.*)$/
+  R_INPUT_RULE = /^(.*)::=:::$/
+  R_OUTPUT_RULE = /^(.*)::=~(.*)$/
+end
+