Support ignore target

8 files changed, 26 insertions, 2 deletions

diff --git a/src/main/java/org/shedlang/compiler/ast/typed/TypedTargetNode.java b/src/main/java/org/shedlang/compiler/ast/typed/TypedTargetNode.java
index 61ead210..1b469175 100644
--- a/src/main/java/org/shedlang/compiler/ast/typed/TypedTargetNode.java
+++ b/src/main/java/org/shedlang/compiler/ast/typed/TypedTargetNode.java
@@ -5,6 +5,7 @@ import org.shedlang.compiler.sources.Source;
 import java.util.List;
 
 public sealed interface TypedTargetNode extends TypedNode {
+    record Ignore(Source source) implements TypedTargetNode {}
     record Reassign(String name, Source source) implements TypedTargetNode {}
     record Tuple(List<TypedTargetNode> elements, Source source) implements TypedTargetNode {}
     record Val(String name, Source source) implements TypedTargetNode {}
diff --git a/src/main/java/org/shedlang/compiler/ast/untyped/UntypedTargetNode.java b/src/main/java/org/shedlang/compiler/ast/untyped/UntypedTargetNode.java
index 3cea8c2d..1d4cbe7e 100644
--- a/src/main/java/org/shedlang/compiler/ast/untyped/UntypedTargetNode.java
+++ b/src/main/java/org/shedlang/compiler/ast/untyped/UntypedTargetNode.java
@@ -5,6 +5,7 @@ import org.shedlang.compiler.sources.Source;
 import java.util.List;
 
 public sealed interface UntypedTargetNode extends UntypedNode {
+    record Ignore(Source source) implements UntypedTargetNode {}
     record Reassign(String name, Source source) implements UntypedTargetNode {}
     record Tuple(List<UntypedTargetNode> elements, Source source) implements UntypedTargetNode {}
     record Val(String name, Source source) implements UntypedTargetNode, UntypedVariableDeclarationNode {}
diff --git a/src/main/java/org/shedlang/compiler/parser/Parser.java b/src/main/java/org/shedlang/compiler/parser/Parser.java
index 44c132e7..eef01d28 100644
--- a/src/main/java/org/shedlang/compiler/parser/Parser.java
+++ b/src/main/java/org/shedlang/compiler/parser/Parser.java
@@ -301,7 +301,7 @@ public class Parser {
 
     static UntypedFunctionStatementNode parseFunctionStatement(TokenIterator<TokenType> tokens) {
         return switch (tokens.peek().tokenType()) {
-            case KEYWORD_ASSIGN, KEYWORD_VAL, KEYWORD_VAR ->
+            case KEYWORD_ASSIGN, KEYWORD_VAL, KEYWORD_VAR, SYMBOL_UNDERSCORE ->
                 parseAssign(tokens);
 
             case KEYWORD_RETURN ->
@@ -633,6 +633,15 @@ public class Parser {
                 yield new UntypedTargetNode.Tuple(elements, source);
             }
 
+            case SYMBOL_UNDERSCORE -> {
+                tokens.skip(TokenType.SYMBOL_UNDERSCORE);
+
+                var end = tokens.position();
+                var source = start.to(end);
+
+                yield new UntypedTargetNode.Ignore(source);
+            }
+
             default ->
                 throw new UnexpectedTokenException("target", tokens.peek());
         };
diff --git a/src/main/java/org/shedlang/compiler/parser/TokenType.java b/src/main/java/org/shedlang/compiler/parser/TokenType.java
index d9cd95aa..53a7877a 100644
--- a/src/main/java/org/shedlang/compiler/parser/TokenType.java
+++ b/src/main/java/org/shedlang/compiler/parser/TokenType.java
@@ -37,4 +37,5 @@ public enum TokenType {
     SYMBOL_PLUS,
     SYMBOL_SEMICOLON,
     SYMBOL_THIN_ARROW,
+    SYMBOL_UNDERSCORE,
 }
diff --git a/src/main/java/org/shedlang/compiler/parser/Tokeniser.java b/src/main/java/org/shedlang/compiler/parser/Tokeniser.java
index 3793417a..bfa75a8e 100644
--- a/src/main/java/org/shedlang/compiler/parser/Tokeniser.java
+++ b/src/main/java/org/shedlang/compiler/parser/Tokeniser.java
@@ -51,7 +51,8 @@ public class Tokeniser {
             RegexTokeniser.rule(TokenType.SYMBOL_PAREN_OPEN, "\\("),
             RegexTokeniser.rule(TokenType.SYMBOL_PAREN_CLOSE, "\\)"),
             RegexTokeniser.rule(TokenType.SYMBOL_PLUS, "\\+"),
-            RegexTokeniser.rule(TokenType.SYMBOL_SEMICOLON, ";")
+            RegexTokeniser.rule(TokenType.SYMBOL_SEMICOLON, ";"),
+            RegexTokeniser.rule(TokenType.SYMBOL_UNDERSCORE, "_")
         )
     );
 
diff --git a/src/main/java/org/shedlang/compiler/stackir/StackCompiler.java b/src/main/java/org/shedlang/compiler/stackir/StackCompiler.java
index d036eebe..07180669 100644
--- a/src/main/java/org/shedlang/compiler/stackir/StackCompiler.java
+++ b/src/main/java/org/shedlang/compiler/stackir/StackCompiler.java
@@ -372,6 +372,10 @@ public class StackCompiler {
         Context context
     ) {
         return switch (target) {
+            case TypedTargetNode.Ignore ignore -> {
+                yield context.addInstruction(new DiscardInstruction(ignore.source()));
+            }
+
             case TypedTargetNode.Reassign reassign -> {
                 context = context.addInstruction(
                     new VarStoreInstruction(
diff --git a/src/main/java/org/shedlang/compiler/typechecker/DeclaredVariables.java b/src/main/java/org/shedlang/compiler/typechecker/DeclaredVariables.java
index 43a087b5..7175f51c 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/DeclaredVariables.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/DeclaredVariables.java
@@ -102,6 +102,9 @@ class DeclaredVariables {
                     VariableType.VAL,
                     val.source()
                 ));
+
+            case UntypedTargetNode.Ignore ignore ->
+                variables;
         };
     }
 }
diff --git a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
index 8f0d363a..2d426428 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
@@ -864,6 +864,10 @@ public class TypeChecker {
         TypeCheckerContext context
     ) {
         return switch (target) {
+            case UntypedTargetNode.Ignore ignore -> {
+                yield context.toResult(new TypedTargetNode.Ignore(target.source()));
+            }
+
             case UntypedTargetNode.Reassign reassign -> {
                 var targetVariableResult = runtimeLookup(
                     reassign.name(),