Type check references

6 files changed, 101 insertions, 4 deletions

diff --git a/src/main/java/org/shedlang/compiler/ast/typed/TypedExpressionNode.java b/src/main/java/org/shedlang/compiler/ast/typed/TypedExpressionNode.java
index f7ce02dc..73ad8991 100644
--- a/src/main/java/org/shedlang/compiler/ast/typed/TypedExpressionNode.java
+++ b/src/main/java/org/shedlang/compiler/ast/typed/TypedExpressionNode.java
@@ -3,7 +3,7 @@ package org.shedlang.compiler.ast.typed;
 import org.shedlang.compiler.sources.Source;
 import org.shedlang.compiler.types.Type;
 
-public sealed interface TypedExpressionNode permits TypedStringLiteralNode {
+public sealed interface TypedExpressionNode permits TypedReferenceNode, TypedStringLiteralNode {
     Source source();
     Type type();
 }
diff --git a/src/main/java/org/shedlang/compiler/ast/typed/TypedReferenceNode.java b/src/main/java/org/shedlang/compiler/ast/typed/TypedReferenceNode.java
new file mode 100644
index 00000000..767cf814
--- /dev/null
+++ b/src/main/java/org/shedlang/compiler/ast/typed/TypedReferenceNode.java
@@ -0,0 +1,11 @@
+package org.shedlang.compiler.ast.typed;
+
+import org.shedlang.compiler.sources.Source;
+import org.shedlang.compiler.types.Type;
+
+public record TypedReferenceNode(
+    String name,
+    Type type,
+    Source source
+) implements TypedExpressionNode {
+}
diff --git a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
index d37eb347..a030f117 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
@@ -1,6 +1,7 @@
 package org.shedlang.compiler.typechecker;
 
 import org.shedlang.compiler.ast.typed.TypedExpressionNode;
+import org.shedlang.compiler.ast.typed.TypedReferenceNode;
 import org.shedlang.compiler.ast.typed.TypedStringLiteralNode;
 import org.shedlang.compiler.ast.untyped.UntypedCallNode;
 import org.shedlang.compiler.ast.untyped.UntypedExpressionNode;
@@ -17,13 +18,39 @@ public class TypeChecker {
     ) {
         return switch (untyped) {
             case UntypedStringLiteralNode untypedStringLiteral ->
-                new TypedStringLiteralNode(untypedStringLiteral.value(), untypedStringLiteral.source());
+                typeCheckStringLiteral(untypedStringLiteral);
 
             case UntypedCallNode untypedCall ->
                 throw new UnsupportedOperationException("TODO");
 
             case UntypedReferenceNode untypedReference ->
-                throw new UnsupportedOperationException("TODO");
+                typeCheckReference(untypedReference, context);
         };
     }
+
+    private static TypedReferenceNode typeCheckReference(
+        UntypedReferenceNode untyped,
+        TypeCheckerContext context
+    ) {
+        var type = context.environment(untyped.name());
+
+        if (type.isEmpty()) {
+            throw new UnknownVariableError(untyped.name(), untyped.source());
+        }
+
+        return new TypedReferenceNode(
+            untyped.name(),
+            type.get(),
+            untyped.source()
+        );
+    }
+
+    private static TypedStringLiteralNode typeCheckStringLiteral(
+        UntypedStringLiteralNode untypedStringLiteral
+    ) {
+        return new TypedStringLiteralNode(
+            untypedStringLiteral.value(),
+            untypedStringLiteral.source()
+        );
+    }
 }
diff --git a/src/main/java/org/shedlang/compiler/typechecker/TypeCheckerContext.java b/src/main/java/org/shedlang/compiler/typechecker/TypeCheckerContext.java
index 261e3e95..c130b0d3 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/TypeCheckerContext.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/TypeCheckerContext.java
@@ -1,5 +1,27 @@
 package org.shedlang.compiler.typechecker;
 
+import org.pcollections.Empty;
+import org.pcollections.PMap;
+import org.shedlang.compiler.types.Type;
+
+import java.util.Optional;
+
 public class TypeCheckerContext {
-    public static final TypeCheckerContext EMPTY = new TypeCheckerContext();
+    public static final TypeCheckerContext EMPTY = new TypeCheckerContext(
+        Empty.map()
+    );
+
+    private final PMap<String, Type> environment;
+
+    public TypeCheckerContext(PMap<String, Type> environment) {
+        this.environment = environment;
+    }
+
+    public TypeCheckerContext enter(PMap<String, Type> environment) {
+        return new TypeCheckerContext(this.environment.plusAll(environment));
+    }
+
+    public Optional<Type> environment(String name) {
+        return Optional.ofNullable(environment.get(name));
+    }
 }
diff --git a/src/main/java/org/shedlang/compiler/typechecker/UnknownVariableError.java b/src/main/java/org/shedlang/compiler/typechecker/UnknownVariableError.java
new file mode 100644
index 00000000..91ab3fae
--- /dev/null
+++ b/src/main/java/org/shedlang/compiler/typechecker/UnknownVariableError.java
@@ -0,0 +1,17 @@
+package org.shedlang.compiler.typechecker;
+
+import org.shedlang.compiler.errors.SourceError;
+import org.shedlang.compiler.sources.Source;
+
+public class UnknownVariableError extends SourceError {
+    private final String variableName;
+
+    public UnknownVariableError(String variableName, Source source) {
+        super("Unknown variable: " + variableName, source);
+        this.variableName = variableName;
+    }
+
+    public String variableName() {
+        return variableName;
+    }
+}
diff --git a/src/main/java/org/shedlang/compiler/util/P.java b/src/main/java/org/shedlang/compiler/util/P.java
new file mode 100644
index 00000000..7ce8232c
--- /dev/null
+++ b/src/main/java/org/shedlang/compiler/util/P.java
@@ -0,0 +1,20 @@
+package org.shedlang.compiler.util;
+
+import org.pcollections.HashTreePMap;
+import org.pcollections.PMap;
+
+import java.util.Map;
+
+public class P {
+    private P() {
+    }
+
+    @SafeVarargs
+    public static <K, V> PMap<K, V> map(Map.Entry<K, V>... entries) {
+        var map = HashTreePMap.<K, V>empty();
+        for (var entry : entries) {
+            map = map.plus(entry.getKey(), entry.getValue());
+        }
+        return map;
+    }
+}