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/lex.rb | 91 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 91 insertions(+)
 create mode 100644 lib/sexp/lex.rb

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

diff --git a/lib/sexp/lex.rb b/lib/sexp/lex.rb
new file mode 100644
index 0000000..d148840
--- /dev/null
+++ b/lib/sexp/lex.rb
@@ -0,0 +1,91 @@
+class Token
+  def initialize(content = nil)
+    @content = content
+  end
+
+  attr_reader :content
+
+  alias token class
+
+  def to_s
+    case self
+    when T_End
+      "END"
+    when T_LParen
+      "LEFT_PAREN"
+    when T_RParen
+      "RIGHT_PAREN"
+    when T_Whitespace
+      "WHITESPACE"
+    when T_Atom
+      "ATOM:\"#{content}\""
+    end
+  end
+
+  def self.end; T_End.new; end
+  def self.lparen; T_LParen.new; end
+  def self.rparen; T_RParen.new; end
+  def self.whitespace; T_Whitespace.new; end
+  def self.atom(content); T_Atom.new(content); end
+end
+
+class T_End < Token; end
+class T_LParen < Token; end
+class T_RParen < Token; end
+class T_Whitespace < Token; end
+class T_Atom < Token; end
+
+def peek_char(input)
+  input.first
+end
+
+def consume_char(input)
+  input.shift
+end
+
+def consume_whitespace(input)
+  while [?\s, ?\t, ?\r, ?\n].include?(peek_char(input))
+    consume_char(input)
+  end
+end
+
+def get_atom(input)
+  val = ""
+  until [?(, ?), ?\s, ?\t, ?\r, ?\n].include?(peek_char(input))
+    val += consume_char(input)
+  end
+  val
+end
+
+def lex_token(input)
+  case peek_char(input)
+  when nil
+    Token.end
+  when ?(
+    consume_char(input)
+    Token.lparen
+  when ?)
+    consume_char(input)
+    Token.rparen
+  when ?\s, ?\t, ?\r, ?\n
+    consume_whitespace(input)
+    Token.whitespace
+  else
+    val = get_atom(input)
+    Token.atom(val)
+  end
+end
+
+def lex_tokens(input)
+  input = input.chars
+
+  toks = []
+
+  loop do
+    tok = lex_token(input)
+    break if tok.token == T_End
+    toks << tok if [T_LParen, T_RParen, T_Atom].include?(tok.token)
+  end
+
+  toks
+end
-- 
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