From 7c358460db1c42a5b7e79b7c6706ebf2adcff39f Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Tue, 6 Jun 2023 19:15:42 +0100
Subject: Parse references

---
 .../compiler/ast/UntypedExpressionNode.java        |  2 +-
 .../compiler/ast/UntypedReferenceNode.java         |  6 ++++++
 .../java/org/shedlang/compiler/parser/Parser.java  | 25 +++++++++++++++++-----
 3 files changed, 27 insertions(+), 6 deletions(-)
 create mode 100644 src/main/java/org/shedlang/compiler/ast/UntypedReferenceNode.java

(limited to 'src/main/java')

diff --git a/src/main/java/org/shedlang/compiler/ast/UntypedExpressionNode.java b/src/main/java/org/shedlang/compiler/ast/UntypedExpressionNode.java
index 03988b0d..0799550b 100644
--- a/src/main/java/org/shedlang/compiler/ast/UntypedExpressionNode.java
+++ b/src/main/java/org/shedlang/compiler/ast/UntypedExpressionNode.java
@@ -1,5 +1,5 @@
 package org.shedlang.compiler.ast;
 
 public sealed interface UntypedExpressionNode extends UntypedNode
-    permits UntypedStringLiteralNode {
+    permits UntypedReferenceNode, UntypedStringLiteralNode {
 }
diff --git a/src/main/java/org/shedlang/compiler/ast/UntypedReferenceNode.java b/src/main/java/org/shedlang/compiler/ast/UntypedReferenceNode.java
new file mode 100644
index 00000000..721a409f
--- /dev/null
+++ b/src/main/java/org/shedlang/compiler/ast/UntypedReferenceNode.java
@@ -0,0 +1,6 @@
+package org.shedlang.compiler.ast;
+
+import org.shedlang.compiler.sources.Source;
+
+public record UntypedReferenceNode(String name, Source source) implements UntypedExpressionNode {
+}
diff --git a/src/main/java/org/shedlang/compiler/parser/Parser.java b/src/main/java/org/shedlang/compiler/parser/Parser.java
index 0e838b28..d4383fda 100644
--- a/src/main/java/org/shedlang/compiler/parser/Parser.java
+++ b/src/main/java/org/shedlang/compiler/parser/Parser.java
@@ -2,6 +2,7 @@ package org.shedlang.compiler.parser;
 
 import org.shedlang.compiler.ast.UntypedExpressionNode;
 import org.shedlang.compiler.ast.UntypedNamespaceNode;
+import org.shedlang.compiler.ast.UntypedReferenceNode;
 import org.shedlang.compiler.ast.UntypedStringLiteralNode;
 import org.shedlang.compiler.sources.Source;
 import org.shedlang.compiler.tokeniser.TokenIterator;
@@ -54,11 +55,14 @@ public class Parser {
     }
 
     static UntypedExpressionNode parseTopLevelExpression(TokenIterator<TokenType> tokens) {
-        if (tokens.isNext(TokenType.STRING)) {
-            return parseStringLiteral(tokens);
-        } else {
-            throw new UnexpectedTokenException("expression", tokens.peek());
-        }
+        return switch (tokens.peek().tokenType()) {
+
+            case IDENTIFIER -> parseReference(tokens);
+
+            case STRING -> parseStringLiteral(tokens);
+
+            default -> throw new UnexpectedTokenException("expression", tokens.peek());
+        };
     }
 
     static UntypedNamespaceNode parseNamespace(TokenIterator<TokenType> tokens) {
@@ -68,4 +72,15 @@ public class Parser {
         var source = start.to(end);
         return new UntypedNamespaceNode(source);
     }
+
+    private static UntypedExpressionNode parseReference(TokenIterator<TokenType> tokens) {
+        var start = tokens.position();
+
+        var name = tokens.nextValue(TokenType.IDENTIFIER);
+
+        var end = tokens.position();
+        var source = start.to(end);
+
+        return new UntypedReferenceNode(name, source);
+    }
 }
-- 
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