read varexp

Author: h908714124

src/main/java/io/polypen/parse/Parser.java

@@ -25,27 +25,67 @@ private static ListExpr parse(PushbackReader reader) throws IOException {
                 }
                 default -> {
                     reader.unread(c);
-                    Expr atom = readAtom(reader);
-                    result.add(atom);
+                    Expr word = readWord(reader);
+                    result.add(word);
                 }
             }
+            consumeWhitespace(reader);
         }
         return new ListExpr(result);
     }
 
-    private static Expr readAtom(PushbackReader reader) throws IOException {
-        consumeWhitespace(reader);
+    private static Expr readWord(PushbackReader reader) throws IOException {
+        int c = reader.read();
+        if (c == -1) {
+            return null;
+        }
+        if (c == '*') {
+            return MULT;
+        }
+        if (c == '+') {
+            return PLUS;
+        }
+        if (c == '-') {
+            return MINUS;
+        }
+        reader.unread(c);
+        if (Character.isDigit(c)) {
+            return readNumber(reader);
+        }
+        return readVarExp(reader);
+    }
+
+    private static NumberExpr readNumber(PushbackReader reader) throws IOException {
         StringBuilder sb = new StringBuilder();
         int c;
-        while ((c = reader.read()) != -1) {
-            if (c != ' ' && c != '(' && c != ')') {
-                sb.append((char) c);
+        while (Character.isDigit(c = reader.read())) {
+            sb.append((char) c);
+        }
+        if (c != -1) {
+            reader.unread(c);
+        }
+        return new NumberExpr(Integer.parseInt(sb.toString()));
+    }
+
+    private static VarExp readVarExp(PushbackReader reader) throws IOException {
+        StringBuilder name = new StringBuilder();
+        int c;
+        while (true) {
+            c = reader.read();
+            if (Character.isAlphabetic(c) || Character.isDigit(c) || c == '_') {
+                name.append((char) c);
             } else {
-                reader.unread(c);
                 break;
             }
         }
-        return new Atom(sb.toString());
+        if (c == '^') {
+            NumberExpr expr = readNumber(reader);
+            return new VarExp(name.toString(), expr.value);
+        }
+        if (c != -1) {
+            reader.unread(c);
+        }
+        return new VarExp(name.toString(), 1);
     }
 
     private static void consumeWhitespace(PushbackReader reader) throws IOException {
@@ -71,10 +111,34 @@ public static ListExpr parse(String s) {
     public interface Expr {
     }
 
-    public record Atom(String value) implements Expr {
+    public static final Expr PLUS = new Expr() {
+        @Override
+        public String toString() {
+            return "+";
+        }
+    };
+
+    public static final Expr MINUS = new Expr() {
+        @Override
+        public String toString() {
+            return "-";
+        }
+    };
+
+    public static final Expr MULT = new Expr() {
+        @Override
+        public String toString() {
+            return "*";
+        }
+    };
+
+    public record ListExpr(List<Expr> value) implements Expr {
+    }
+
+    public record NumberExpr(int value) implements Expr {
     }
 
-    public record ListExpr(List<Expr> values) implements Expr {
+    public record VarExp(String var, int exp) implements Expr {
     }
 
     private Parser() {

src/test/java/io/polypen/parse/ParserTest.java

@@ -6,7 +6,7 @@ class ParserTest {
 
     @Test
     void parse() {
-        Parser.ListExpr result = Parser.parse("(a b) 2 3");
+        Parser.ListExpr result = Parser.parse("(a_1^12 + b12^2) * 2");
         System.out.println(result);
     }
 }