From ff4dad7fc61d13aee7ed1191cc3afd9a8a75a240 Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Sat, 10 Jun 2023 12:04:59 +0100
Subject: Compile expression statements to stack instructions

---
 .../shedlang/compiler/stackir/StackCompiler.java   | 11 ++++++++++
 .../stackir/instructions/DiscardInstruction.java   |  6 ++++++
 .../compiler/stackir/instructions/Instruction.java |  2 +-
 .../org/shedlang/compiler/ast/typed/Typed.java     |  4 ++++
 .../StackCompilerExpressionStatementTests.java     | 24 ++++++++++++++++++++++
 .../stackir/instructions/InstructionMatchers.java  |  6 ++++++
 .../TypeCheckerExpressionStatementTests.java       |  8 --------
 7 files changed, 52 insertions(+), 9 deletions(-)
 create mode 100644 src/main/java/org/shedlang/compiler/stackir/instructions/DiscardInstruction.java
 create mode 100644 src/test/java/org/shedlang/compiler/stackir/StackCompilerExpressionStatementTests.java

(limited to 'src')

diff --git a/src/main/java/org/shedlang/compiler/stackir/StackCompiler.java b/src/main/java/org/shedlang/compiler/stackir/StackCompiler.java
index c16674e0..4623bc5d 100644
--- a/src/main/java/org/shedlang/compiler/stackir/StackCompiler.java
+++ b/src/main/java/org/shedlang/compiler/stackir/StackCompiler.java
@@ -56,6 +56,17 @@ public class StackCompiler {
         };
     }
 
+    private static PVector<Instruction> compileExpressionStatement(TypedExpressionStatementNode node) {
+        return compileExpression(node.expression()).plus(new DiscardInstruction(node.source()));
+    }
+    
+    public static PVector<Instruction> compileFunctionStatement(TypedFunctionStatementNode node) {
+        return switch (node) {
+            case TypedExpressionStatementNode expressionStatement ->
+                compileExpressionStatement(expressionStatement);  
+        };
+    }
+
     private static PVector<Instruction> compileIntLiteral(TypedIntLiteralNode node) {
         return P.vector(new PushIntInstruction(node.value(), node.source()));
     }
diff --git a/src/main/java/org/shedlang/compiler/stackir/instructions/DiscardInstruction.java b/src/main/java/org/shedlang/compiler/stackir/instructions/DiscardInstruction.java
new file mode 100644
index 00000000..6efd3c03
--- /dev/null
+++ b/src/main/java/org/shedlang/compiler/stackir/instructions/DiscardInstruction.java
@@ -0,0 +1,6 @@
+package org.shedlang.compiler.stackir.instructions;
+
+import org.shedlang.compiler.sources.Source;
+
+public record DiscardInstruction(Source source) implements Instruction {
+}
diff --git a/src/main/java/org/shedlang/compiler/stackir/instructions/Instruction.java b/src/main/java/org/shedlang/compiler/stackir/instructions/Instruction.java
index 33007bf2..0b5d9dd8 100644
--- a/src/main/java/org/shedlang/compiler/stackir/instructions/Instruction.java
+++ b/src/main/java/org/shedlang/compiler/stackir/instructions/Instruction.java
@@ -1,5 +1,5 @@
 package org.shedlang.compiler.stackir.instructions;
 
 public sealed interface Instruction
-    permits CallInstruction, LocalLoadInstruction, LocalStoreInstruction, PushBoolInstruction, PushIntInstruction, PushStringInstruction {
+    permits CallInstruction, DiscardInstruction, LocalLoadInstruction, LocalStoreInstruction, PushBoolInstruction, PushIntInstruction, PushStringInstruction {
 }
diff --git a/src/test/java/org/shedlang/compiler/ast/typed/Typed.java b/src/test/java/org/shedlang/compiler/ast/typed/Typed.java
index ed58b4d4..80c02765 100644
--- a/src/test/java/org/shedlang/compiler/ast/typed/Typed.java
+++ b/src/test/java/org/shedlang/compiler/ast/typed/Typed.java
@@ -29,6 +29,10 @@ public class Typed {
         );
     }
 
+    public static TypedExpressionStatementNode expressionStatement(TypedExpressionNode expression) {
+        return new TypedExpressionStatementNode(expression, Sources.NULL);
+    }
+
     public static TypedIntLiteralNode intLiteral(int value) {
         return new TypedIntLiteralNode(BigInteger.valueOf(value), Sources.NULL);
     }
diff --git a/src/test/java/org/shedlang/compiler/stackir/StackCompilerExpressionStatementTests.java b/src/test/java/org/shedlang/compiler/stackir/StackCompilerExpressionStatementTests.java
new file mode 100644
index 00000000..a408f19d
--- /dev/null
+++ b/src/test/java/org/shedlang/compiler/stackir/StackCompilerExpressionStatementTests.java
@@ -0,0 +1,24 @@
+package org.shedlang.compiler.stackir;
+
+import org.junit.jupiter.api.Test;
+import org.shedlang.compiler.ast.typed.Typed;
+
+import java.util.List;
+
+import static org.shedlang.compiler.stackir.instructions.InstructionMatchers.*;
+import static org.zwobble.precisely.AssertThat.assertThat;
+import static org.zwobble.precisely.Matchers.isSequence;
+
+public class StackCompilerExpressionStatementTests {
+    @Test
+    public void expressionIsEvaluatedAndTheResultDiscarded() {
+        var node = Typed.expressionStatement(Typed.stringLiteral("hello"));
+
+        var instructions = StackCompiler.compileFunctionStatement(node);
+
+        assertThat(instructions, isSequence(
+            isPushStringInstruction("hello"),
+            isDiscardInstruction()
+        ));
+    }
+}
diff --git a/src/test/java/org/shedlang/compiler/stackir/instructions/InstructionMatchers.java b/src/test/java/org/shedlang/compiler/stackir/instructions/InstructionMatchers.java
index c9cd8621..3863c2f9 100644
--- a/src/test/java/org/shedlang/compiler/stackir/instructions/InstructionMatchers.java
+++ b/src/test/java/org/shedlang/compiler/stackir/instructions/InstructionMatchers.java
@@ -19,6 +19,12 @@ public class InstructionMatchers {
         );
     }
 
+    public static Matcher<Instruction> isDiscardInstruction() {
+        return instanceOf(
+            DiscardInstruction.class
+        );
+    }
+
     public static Matcher<Instruction> isLocalLoadInstruction(String name) {
         return instanceOf(
             LocalLoadInstruction.class,
diff --git a/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerExpressionStatementTests.java b/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerExpressionStatementTests.java
index 29175665..a475ed6c 100644
--- a/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerExpressionStatementTests.java
+++ b/src/test/java/org/shedlang/compiler/typechecker/TypeCheckerExpressionStatementTests.java
@@ -1,19 +1,11 @@
 package org.shedlang.compiler.typechecker;
 
 import org.junit.jupiter.api.Test;
-import org.shedlang.compiler.ast.typed.Typed;
 import org.shedlang.compiler.ast.untyped.Untyped;
-import org.shedlang.compiler.typechecker.errors.UnknownVariableError;
-import org.shedlang.compiler.types.Types;
-import org.shedlang.compiler.util.P;
 
-import java.util.Map;
-
-import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.shedlang.compiler.ast.typed.TypedNodeMatchers.isTypedExpressionStatementNode;
 import static org.shedlang.compiler.ast.typed.TypedNodeMatchers.isTypedStringLiteralNode;
 import static org.zwobble.precisely.AssertThat.assertThat;
-import static org.zwobble.precisely.Matchers.equalTo;
 
 public class TypeCheckerExpressionStatementTests {
     @Test
-- 
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