Java instructions

README.md

@@ -48,7 +48,7 @@ Material: plt = course book, dragon = Dragon book. Slides follow closely the plt
 | Tue 19/11 | 13-15 | Type checking | [slides](plt-book/ipl-book/slides/4-slides-ipl-book.pdf), plt 4, dragon 5,6, [script](notes/type-checking.html), [prime.c](notes/prime.c), [prime-stms.c](notes/prime-stms.c), [division.c](notes/division.c), [division-annotated.c](notes/division-annotated.c) |
 | Thu 21/11 | 13-15 | Interpreting | [slides](plt-book/ipl-book/slides/5-slides-ipl-book.pdf), plt 5, [script](notes/interpreter.html) |
 | Tue 26/11 | 13-14 | Hands-on with Lab 2 (Haskell) |  [script](notes/monads.html) |
-| Tue 26/11 | 14-15 | Hands-on with Lab 2 (Java)    | |
+| Tue 26/11 | 14-15 | Hands-on with Lab 2 (Java)    | [script](notes/java.html) |
 | Thu 28/11 | 13-15 **SB-H5** | Code generation | [slides](plt-book/ipl-book/slides/6-slides-ipl-book.pdf), plt 6, dragon 6,7, [notes](notes/compilation.html), [prime.c](notes/prime.c), [prime.j](notes/prime.j) |
 | Tue 03/12 | 13-14 | Hands-on with Lab 3 (Haskell) |  |
 | Tue 03/12 | 14-15 | Hands-on with Lab 3 (Java)    |  |

notes/Makefile

@@ -1,7 +1,7 @@
 .PHONY: all
 all: index.html
 
-files = type-checking.html interpreter.html monads.html compilation.html cbn-cbv.html typing.html LR-table.html git-primer.html
+files = type-checking.html interpreter.html monads.html compilation.html cbn-cbv.html typing.html LR-table.html git-primer.html java.html
 
 index.html : $(files)
 	tree -H '.' -L 2 --noreport --charset utf-8 > $@

notes/java.md

@@ -0,0 +1,52 @@
+# Recommendations for solving lab 2 with Java
+
+The stub for lab 2 uses Java 21,
+which admits a more readable alternative to the visitor pattern suggested in the book.
+The following example code shows how you can process an object ```exp``` of the type type ```Exp```
+generated by the parser defined in the stub.
+
+```java
+switch(exp) {
+    case EInt    e -> ... ;
+    case EDouble e -> ... ;
+    case EAnd    e -> ... ;
+    case EOr    e -> ... ;
+    ...
+    default -> throw new IllegalStateException("Case for " + e + " is not yet implemented.");
+}
+```
+
+On the right hand side of the ```->``` you can extract further information from ```e```,
+for example, in the case ```EAnd e```, you can use the two operands ```e.exp_1``` and ```e.exp_2```.
+
+```switch```, if used like above produces a Java-expression, which means that you can use it in assignments:
+
+```java
+var typedExpression = switch(exp) { ... }
+```
+
+To define the neccessary datatypes, ```record```s are very useful.
+You can define a record like this:
+
+```java
+public record TypedAnd(TypedExpr e1, TypedExpr e2) {
+}
+```
+
+Objects of this type can be constructed with ```new TypedAnd(e1,e2)``` where ```e1``` and ```e2``` are ```TypedExpr```s. For solving the lab, it is reasonable to define an ```interface``` ```TypedExpr``` with a method which returns the type of an expression:
+
+```java
+public interface TypedExpr {
+  Type type();
+}
+```
+
+Where ```Type``` is a datatype for types that needs to be defined. With this interface, the ```TypedAnd``` from above can be turned into an implementation like this:
+
+```java
+public record TypedAnd(TypedExpr e1, TypedExpr e2) {
+  Type type() {
+    return new Type.Bool; // this is what it could look like if you implement basic types as an enum
+  }
+}
+```