From 3f0f8ab5e71f2b625b863581bb22c1dca08ba11a Mon Sep 17 00:00:00 2001
From: Slavasil <subvia@proton.me>
Date: Mon, 16 Mar 2026 13:07:49 +0300
Subject: [PATCH] implement expression parser

---
 lib/ruby_algebra.rb        |   1 +
 lib/ruby_algebra/parser.rb | 177 +++++++++++++++++++++++++++++++++++++
 2 files changed, 178 insertions(+)
 create mode 100644 lib/ruby_algebra/parser.rb

diff --git a/lib/ruby_algebra.rb b/lib/ruby_algebra.rb
index cd719d2..b9b54c4 100644
--- a/lib/ruby_algebra.rb
+++ b/lib/ruby_algebra.rb
@@ -2,6 +2,7 @@
 
 require_relative "ruby_algebra/version"
 require_relative "ruby_algebra/expression"
+require_relative "ruby_algebra/parser"
 
 module RubyAlgebra
 end
diff --git a/lib/ruby_algebra/parser.rb b/lib/ruby_algebra/parser.rb
new file mode 100644
index 0000000..6d58044
--- /dev/null
+++ b/lib/ruby_algebra/parser.rb
@@ -0,0 +1,177 @@
+# frozen_string_literal: true
+
+module RubyAlgebra
+  module Parser
+    class Token
+      attr_reader :type
+    end
+
+    class NumberToken < Token
+      attr_reader :value
+
+      def initialize(value)
+        @type = :num
+        @value = value
+      end
+    end
+
+    class IdentifierToken < Token
+      attr_reader :name
+
+      def initialize(name)
+        @type = :id
+        @name = name
+      end
+    end
+
+    class OperatorToken < Token
+      attr_reader :op
+
+      def initialize(op)
+        @type = :op
+        @op = op
+      end
+    end
+
+    class ParenthesisToken < Token
+      attr_reader :closing
+
+      def initialize(closing)
+        @type = :paren
+        @closing = closing
+      end
+    end
+
+    class EndToken < Token
+      def initialize()
+        @type = :end
+      end
+    end
+
+    def tokenize(e)
+      i = 0
+      add_implicit_mul = false
+      while i < e.length
+        c = e[i]
+        if c.match?(/\p{Alpha}/)
+          yield OperatorToken.new(:mult) if add_implicit_mul
+          j = i + 1
+          j += 1 while j < e.length && e[j].match?(/\p{Alnum}/)
+          add_implicit_mul = true
+          yield IdentifierToken.new(e[i...j])
+          i = j
+        elsif c.match?(/[+\-*\/^()]/)
+          yield OperatorToken.new(:mult) if c == "(" && add_implicit_mul
+          i += 1
+          add_implicit_mul = c == ")"
+          case c
+          when "+"
+            yield OperatorToken.new(:add)
+          when "-"
+            yield OperatorToken.new(:sub)
+          when "*"
+            yield OperatorToken.new(:mult)
+          when "/"
+            yield OperatorToken.new(:div)
+          when "^"
+            yield OperatorToken.new(:pow)
+          when "("
+            yield ParenthesisToken.new(false)
+          when ")"
+            yield ParenthesisToken.new(true)
+          end
+        elsif c.match?(/\p{Digit}|\./)
+          yield OperatorToken.new(:mult) if add_implicit_mul
+          j = i + 1
+          j += 1 while j < e.length && e[j].match?(/\p{Digit}|\./)
+          s = e[i...j]
+          fl = s.count "."
+          if fl > 1
+            raise Exception.new
+          end
+          add_implicit_mul = true
+          if fl == 0
+            yield NumberToken.new(s.to_i)
+          else
+            yield NumberToken.new(s.to_f)
+          end
+          i = j
+        elsif c == " "
+          i += 1
+        else
+          puts "Unrecognized character at pos #{i}"
+          i += 1
+        end
+      end
+      yield EndToken.new
+    end
+
+    def parse(expr)
+      operators = []
+      out_stack = []
+      prev = nil
+      tokenize(expr) do |token|
+        if token.type == :num
+          out_stack.push(Constant.new(token.value))
+        elsif token.type == :end
+          # тут надо обработку незакрытых (
+          _parse_make_op(operators, out_stack) until operators.empty?
+        elsif token.type == :op
+          p = _parse_op_prio token
+          while operators.length != 0 && operators.last.type == :op && (_parse_op_prio(operators.last) > p || (_parse_op_prio(operators.last) == p && token.op != :pow))
+            _parse_make_op(operators, out_stack)
+          end
+          operators.push(token)
+        elsif token.type == :paren
+          if token.closing
+            until operators.empty? || (operators.last.type == :paren && !operators.last.closing)
+              _parse_make_op(operators, out_stack)
+            end
+            if operators.empty? || operators.last.type != :paren || operators.last.closing
+              puts "Missing ( in expression"
+            else
+              operators.pop
+            end
+          else
+            operators.push token
+          end
+        elsif token.type == :id
+          out_stack.push(Variable.new(token.name))
+        end
+        prev = token
+      end
+      out_stack[0]
+    end
+
+    def _parse_make_op(operators, out_stack)
+      oper = operators.pop
+      raise Exception.new unless oper.type == :op
+      raise Exception.new unless out_stack.length >= 2
+      b = out_stack.pop
+      a = out_stack.pop
+      case oper.op
+      when :add
+        out_stack.push Addition.new(a, b)
+      when :sub
+        out_stack.push Subtraction.new(a, b)
+      when :mult
+        out_stack.push Multiplication.new(a, b)
+      when :div
+        out_stack.push Division.new(a, b)
+      when :pow
+        out_stack.push Power.new(a, b)
+      end
+    end
+
+    def _parse_op_prio(op_token)
+      case op_token.op
+      when :add, :sub
+        1
+      when :mult, :div
+        2
+      when :pow
+        3
+      end
+    end
+  end
+end