finish parsing

minlisp.rb

@@ -0,0 +1,38 @@
+# It's a minimal lisp interpreter written in Ruby-lang
+# Author: @vonhyou
+# Start at: Apr. 10, 2021
+
+def tokenize(program)
+  # Convert scripts to token lists
+  replacements = { '(' => ' ( ', ')' => ' ) ' }
+  program.gsub(Regexp.union(replacements.keys), replacements)
+         .split(' ')
+end
+
+def read_tokens(tokens)
+  # read expressions from token
+  raise SyntaxError, 'Unexpected EOF' if tokens.empty?
+
+  token = tokens.shift
+  if token == '('
+    lst = []
+    lst << read_tokens(tokens) while tokens[0] != ')'
+    tokens.shift
+    return lst
+  elsif token == ')'
+    raise SyntaxError, "Unexpected ')'"
+  else
+    return atom token
+  end
+end
+
+def isInteger?(atom) = atom.match?(/^-?\d+$/)
+def isFloat?(atom)   = atom.match?(/^(-?\d+)(\.\d+)?$/)
+
+def atom(token)
+  # Analyse numbers and symbols
+  return Integer token if isInteger? token
+  return Float   token if isFloat?   token
+  token
+end
+