From b9c7fbf5e06630076b93cace17863a6d36125e0d Mon Sep 17 00:00:00 2001
From: Uko Kokņevičs
Date: Sun, 18 Aug 2024 23:45:38 +0800
Subject: Added explicit ignored/"underscore" arguments & top-level defs

---
 ast/src/main/java/lv/enes/orang/ast/ArgSpec.java    |  8 ++++++++
 grammar.bnf                                         |  5 +++--
 lexer/src/main/java/lv/enes/orang/lexer/Lexer.java  |  1 +
 lexer/src/main/java/lv/enes/orang/lexer/Token.java  |  1 +
 .../src/main/java/lv/enes/orang/parser/Parser.java  | 21 +++++++++++++++------
 5 files changed, 28 insertions(+), 8 deletions(-)

diff --git a/ast/src/main/java/lv/enes/orang/ast/ArgSpec.java b/ast/src/main/java/lv/enes/orang/ast/ArgSpec.java
index e167e8f..7fea2f4 100644
--- a/ast/src/main/java/lv/enes/orang/ast/ArgSpec.java
+++ b/ast/src/main/java/lv/enes/orang/ast/ArgSpec.java
@@ -2,9 +2,16 @@ package lv.enes.orang.ast;
 
 public class ArgSpec {
 	public final Type type;
+
+	// non-null if NAMED
 	public final String name;
 
 	private static final ArgSpec NOTHING = new ArgSpec(Type.NOTHING, null);
+	private static final ArgSpec IGNORED = new ArgSpec(Type.IGNORED, null);
+
+	public static ArgSpec ignored() {
+		return IGNORED;
+	}
 
 	public static ArgSpec nothing() {
 		return NOTHING;
@@ -20,6 +27,7 @@ public class ArgSpec {
 	}
 
 	public enum Type {
+		IGNORED,
 		NOTHING,
 		NAMED,
 	}
diff --git a/grammar.bnf b/grammar.bnf
index 9ddaffc..0ac58f9 100644
--- a/grammar.bnf
+++ b/grammar.bnf
@@ -2,9 +2,10 @@
 
 program ::= (statement ';'?)*;
 statement ::= definition | expression;
-definition ::= 'def' def-spec '=' expression;
+definition ::= 'def' def-spec '=' expression
+             | 'def' '_' '=' expression;
 def-spec ::= IDENTIFIER arg-spec*;
-arg-spec ::= IDENTIFIER | '(' ')';
+arg-spec ::= IDENTIFIER | '(' ')' | '_';
 expression ::= binary-expression | unary-expression;
 unary-expression ::= unop+ simple-expression;
 binary-expression ::= call-expression (binop call-expression)*;
diff --git a/lexer/src/main/java/lv/enes/orang/lexer/Lexer.java b/lexer/src/main/java/lv/enes/orang/lexer/Lexer.java
index 8fec98e..50f4d22 100644
--- a/lexer/src/main/java/lv/enes/orang/lexer/Lexer.java
+++ b/lexer/src/main/java/lv/enes/orang/lexer/Lexer.java
@@ -128,6 +128,7 @@ public class Lexer implements Iterator<Token> {
 				if (isIdentInitial(input.peek())) {
 					var ident = readIdentifier();
 					var type = switch (ident) {
+						case "_" -> Token.Type.UNDERSCORE;
 						case "and" -> Token.Type.AND;
 						case "def" -> Token.Type.DEF;
 						case "do" -> Token.Type.DO;
diff --git a/lexer/src/main/java/lv/enes/orang/lexer/Token.java b/lexer/src/main/java/lv/enes/orang/lexer/Token.java
index 59626c7..13236dd 100644
--- a/lexer/src/main/java/lv/enes/orang/lexer/Token.java
+++ b/lexer/src/main/java/lv/enes/orang/lexer/Token.java
@@ -37,6 +37,7 @@ public record Token(Type type, String literal) {
 		LET,
 		THEN,
 		TRUE,
+		UNDERSCORE,
 
 		// Special chars
 		ASTERISK,
diff --git a/parser/src/main/java/lv/enes/orang/parser/Parser.java b/parser/src/main/java/lv/enes/orang/parser/Parser.java
index 6c86e85..3a2e931 100644
--- a/parser/src/main/java/lv/enes/orang/parser/Parser.java
+++ b/parser/src/main/java/lv/enes/orang/parser/Parser.java
@@ -59,11 +59,11 @@ public class Parser {
 		return new Program(Collections.unmodifiableList(statements));
 	}
 
-	private static boolean isBinaryOp(Token token) {
+	private static boolean isNotBinaryOp(Token token) {
 		return switch (token.type()) {
 			case ASTERISK, SLASH, PLUS, MINUS, QUESTION_EQUAL, SLASH_EQUAL, GREATER, GREATER_EQUAL, LESS, LESS_EQUAL
-					-> true;
-			default -> false;
+					-> false;
+			default -> true;
 		};
 	}
 
@@ -143,6 +143,9 @@ public class Parser {
 				consumeToken(Token.Type.PAREN_LEFT);
 				consumeToken(Token.Type.PAREN_RIGHT);
 				argSpecs.add(ArgSpec.nothing());
+			} else if (input.peek().type() == Token.Type.UNDERSCORE) {
+				consumeToken(Token.Type.UNDERSCORE);
+				argSpecs.add(ArgSpec.ignored());
 			} else {
 				break;
 			}
@@ -152,7 +155,7 @@ public class Parser {
 
 	private Expression parseBinaryExpression() throws ParserException {
 		var lhs = parseCallExpression();
-		if (!isBinaryOp(input.peek())) {
+		if (isNotBinaryOp(input.peek())) {
 			return lhs;
 		}
 
@@ -161,7 +164,7 @@ public class Parser {
 
 	private Expression parseBinaryExpressionRhs(Expression lhs, BinaryExpression.Operator op) throws ParserException {
 		var rhs = parseCallExpression();
-		if (!isBinaryOp(input.peek())) {
+		if (isNotBinaryOp(input.peek())) {
 			return new BinaryExpression(op, lhs, rhs);
 		}
 
@@ -187,11 +190,17 @@ public class Parser {
 		return callee;
 	}
 
-	private Definition parseDefinition() throws ParserException {
+	private Statement parseDefinition() throws ParserException {
 		consumeToken(Token.Type.DEF);
+		if (maybeConsumeToken(Token.Type.UNDERSCORE)) {
+			consumeToken(Token.Type.EQUAL);
+			return new ExpressionStatement(parseExpression());
+		}
+
 		var defSpec = parseDefSpec();
 		consumeToken(Token.Type.EQUAL);
 		var value = parseExpression();
+
 		if (defSpec.args().isEmpty()) {
 			return new Definition(defSpec.name(), value);
 		} else {
-- 
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