From 703595f8f8380acc6816f0a770afee6acba8adc4 Mon Sep 17 00:00:00 2001
From: Nat Lasseter <user@4574.co.uk>
Date: Tue, 30 Jan 2024 16:55:42 +0000
Subject: Initial commit

---
 lib/sexp/parse.rb | 118 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 118 insertions(+)
 create mode 100644 lib/sexp/parse.rb

(limited to 'lib/sexp/parse.rb')

diff --git a/lib/sexp/parse.rb b/lib/sexp/parse.rb
new file mode 100644
index 0000000..adfd513
--- /dev/null
+++ b/lib/sexp/parse.rb
@@ -0,0 +1,118 @@
+class Atom
+  def initialize(content = nil)
+    @content = content
+  end
+
+  attr_reader :content
+
+  def to_s
+    content
+  end
+
+  def self.from_token(token)
+    new(token.content)
+  end
+end
+
+class SExp
+  def initialize(addr = nil, data = nil)
+    @addr = addr
+    @data = data
+  end
+
+  def car
+    @addr
+  end
+  def car=(addr)
+    @addr = addr
+  end
+
+  def cdr
+    @data
+  end
+  def cdr=(data)
+    @data = data
+  end
+
+  def to_s
+    if car.nil?
+      "()"
+    elsif cdr.nil?
+      "(#{car} . ())"
+    else
+      "(#{car} . #{cdr})"
+    end
+  end
+end
+
+def peek_token(tokens)
+  tokens.first
+end
+
+def get_token(tokens)
+  tokens.shift
+end
+
+def num_members(tokens)
+  members = 0
+  level = 1
+  at = 1
+
+  until level == 0
+    case tokens.at(at)
+    when T_LParen
+      members += 1 if level == 1
+      level += 1
+    when T_RParen
+      level -= 1
+    when T_Atom
+      members += 1 if level == 1
+    end
+    at += 1
+  end
+
+  members
+end
+
+def members_to_tree(members)
+  case members.length
+  when 0
+    nil
+  when 1
+    SExp.new(members[0], SExp.new)
+  when 2
+    SExp.new(members[0], members[1])
+  else
+    SExp.new(members[0], members_to_tree(members[1..-1]))
+  end
+end
+
+def parse_sexp(tokens)
+  need = num_members(tokens)
+  get_token(tokens)
+  
+  members = []
+
+  need.times do
+    case peek_token(tokens)
+    when T_Atom
+      members << Atom.from_token(get_token(tokens))
+    when T_LParen
+      members << parse_sexp(tokens)
+    end
+  end
+
+  get_token(tokens)
+
+  members_to_tree(members)
+end
+
+def parse_sexps(tokens)
+  sexps = []
+
+  until tokens.empty?
+    sexps << parse_sexp(tokens)
+  end
+
+  sexps
+end
-- 
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