3 files changed, 131 insertions, 0 deletions
diff --git a/calculator-java/src/main/java/CalculatorLexer.java b/calculator-java/src/main/java/CalculatorLexer.java
new file mode 100644
index 0000000..61b906c
--- /dev/null
+++ b/calculator-java/src/main/java/CalculatorLexer.java
@@ -0,0 +1,105 @@
+// Lexer for classical arithmetic expressions with identifiers and assignements.
+// Scans a source string char by char.
+
+import exceptions.LexerException;
+
+public class CalculatorLexer {
+
+  private String src;  // source string for lexical analysis
+  private int idx;     // current index in source
+  private int len;     // length of source
+
+  public CalculatorLexer() { }
+
+  public void initLexer(String source) {
+    this.src = source;
+    idx = 0;
+    len = src.length();
+  }
+
+  // Consumes letters only and builds an identifier
+  private String identifier() {
+    StringBuffer s = new StringBuffer();
+  
+    do {
+      s.append(src.charAt(idx));
+      idx++;
+    } while (idx < len && Character.isLetter(src.charAt(idx)));
+    return s.toString();
+  }
+
+  // Consumes digits and convert integer part and decimal part
+  // Convert characters using the formula
+  // "3456.253" = [(((3+0)*10+4)*10+5)*10+6]+[0.1*2+0.01*5+0.001*3]
+  private double number() throws LexerException {
+    double v = 0;        // accumulates the result
+    double factor = 0.1; // factor for decimal part
+
+    do { // integer part
+      v = v * 10 + Character.digit(src.charAt(idx),30);
+      idx++;
+    } while (idx < len && Character.isDigit(src.charAt(idx)));
+    if (idx < len && src.charAt(idx) == '.') { // decimal point
+      idx++; 
+      if (idx < len && Character.isDigit(src.charAt(idx))) { // decimal part
+        while (idx < len && Character.isDigit(src.charAt(idx))) {
+          v = v + (factor * Character.digit(src.charAt(idx),30));
+          factor = factor * 0.1;
+          idx++;
+        }
+      }
+      else throw new LexerException("Illegal number: decimal part missing");
+    }
+    return v;
+  }
+
+  // Skips blanks, tabs, newlines
+  private void skip() {
+    char c;
+    while (idx < len) {
+      c = src.charAt(idx);
+      if (c==' ' || c=='\t' || c=='\n') idx++;
+      else break;
+    }
+  }
+
+  // returns next token 
+  public Token nextToken() throws LexerException {
+    Token tok = new Token();
+
+    skip();
+    if (idx>=len) {
+	tok.str="EOL";
+	tok.type=Token.EOL;
+    }
+    else
+      // is it a positive number?
+      if (Character.isDigit(src.charAt(idx))) {
+        tok.value = number();
+        tok.type  = Token.NUM;
+        tok.str   = Double.toString(tok.value);
+      }
+      else
+        if (Character.isLetter(src.charAt(idx))) {
+          tok.value = 0;  
+          tok.type  = Token.ID;
+          tok.str   = identifier();
+          if (tok.str.compareTo("let")==0)  tok.type = Token.LET;
+          if (tok.str.compareTo("exit")==0) tok.type = Token.END;
+        }
+        else {
+          switch (src.charAt(idx)) {
+            case '+': tok.type = Token.ADD; tok.str = "+"; break;
+            case '-': tok.type = Token.SUB; tok.str = "-"; break;
+            case '*': tok.type = Token.MUL; tok.str = "*"; break;
+            case '/': tok.type = Token.DIV; tok.str = "/"; break;
+            case '(': tok.type = Token.PAL; tok.str = "("; break;
+            case ')': tok.type = Token.PAR; tok.str = ")"; break;
+            case '=': tok.type = Token.EQU; tok.str = "="; break;
+            default : throw new LexerException("Illegal Token: '" + src.charAt(idx) + "'");
+          }
+          idx++;
+        }
+    return tok;
+  }
+}
+\ No newline at end of file
diff --git a/calculator-java/src/main/java/Token.java b/calculator-java/src/main/java/Token.java
new file mode 100644
index 0000000..4fe8b23
--- /dev/null
+++ b/calculator-java/src/main/java/Token.java
@@ -0,0 +1,21 @@
+// Various Tokens for arithmetic expressions based on integers 
+// with identifiers and assignments
+
+public class Token {
+  public int type;                   // token type
+  public double value;               // numerical value for NUM
+  public String str;                 // token string
+
+  public static final int EOL=0;     // End Of Line
+  public static final int PAL=1;     // Left Parenthesis
+  public static final int PAR=2;     // Right Parenthesis
+  public static final int ADD=3;     // operators
+  public static final int SUB=4;
+  public static final int MUL=5;
+  public static final int DIV=6;
+  public static final int NUM=7;     // number
+  public static final int EQU=8;     // equal 
+  public static final int LET=9;     // let
+  public static final int ID=10;     // identifier
+  public static final int END=11;    // exit
+}
diff --git a/calculator-java/src/main/java/exceptions/LexerException.java b/calculator-java/src/main/java/exceptions/LexerException.java
new file mode 100644
index 0000000..b7b1f24
--- /dev/null
+++ b/calculator-java/src/main/java/exceptions/LexerException.java
@@ -0,0 +1,5 @@
+package exceptions;
+
+public class LexerException extends RuntimeException {
+    public LexerException(String s) { super(s); }
+}
+\ No newline at end of file