From 6c4f39708bfa0c1d8d9afab299ef538c6183204e Mon Sep 17 00:00:00 2001
From: Uko Kokņevičs
Date: Sun, 18 Aug 2024 23:56:26 +0800
Subject: Changed the grammar to allow bare top-level expressions only in REPL.

---
 grammar.bnf                                        |  5 +++-
 orang/src/main/java/lv/enes/orang/Main.java        |  4 ++--
 .../src/main/java/lv/enes/orang/parser/Parser.java | 27 ++++++++++++++++------
 3 files changed, 26 insertions(+), 10 deletions(-)

diff --git a/grammar.bnf b/grammar.bnf
index 0ac58f9..a9e21cb 100644
--- a/grammar.bnf
+++ b/grammar.bnf
@@ -1,7 +1,7 @@
 // Comments are introduced by # and terminated by newline
 
 program ::= (statement ';'?)*;
-statement ::= definition | expression;
+statement ::= definition;
 definition ::= 'def' def-spec '=' expression
              | 'def' '_' '=' expression;
 def-spec ::= IDENTIFIER arg-spec*;
@@ -31,3 +31,6 @@ let-in-expression ::= 'let' def-spec '=' expression ('and' def-spec '=' expressi
 fn-expression ::= 'fn' arg-spec+ '->' expression
                 | 'fn' arg-spec+ do-expression;
 do-expression ::= 'do' expression (';' expression)* 'end';
+
+repl-program ::= (repl-statement ';'?)* '\n'; // currently, hard-limited by the newline :sweat_smile:
+repl-statement ::= statement | expression;
\ No newline at end of file
diff --git a/orang/src/main/java/lv/enes/orang/Main.java b/orang/src/main/java/lv/enes/orang/Main.java
index eb4bfcc..7175dac 100644
--- a/orang/src/main/java/lv/enes/orang/Main.java
+++ b/orang/src/main/java/lv/enes/orang/Main.java
@@ -10,7 +10,7 @@ import static lv.enes.orang.State.STDIN;
 import static lv.enes.orang.State.STDOUT;
 
 public class Main {
-	public static final String PROMPT = ">> ";
+	public static final String PROMPT = "orang-user> ";
 
 	public static void main() throws IOException {
 		repl();
@@ -66,7 +66,7 @@ public class Main {
 			}
 
 			try {
-				var prog = Parser.parseProgram(line);
+				var prog = Parser.parseReplProgram(line);
 				evaluator = evaluator.visitProgram(prog);
 				if (evaluator.lastResult() != null) {
 					STDOUT.print("-> ");
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 3a2e931..9103123 100644
--- a/parser/src/main/java/lv/enes/orang/parser/Parser.java
+++ b/parser/src/main/java/lv/enes/orang/parser/Parser.java
@@ -27,9 +27,9 @@ public class Parser {
 		return parser.parseProgram();
 	}
 
-	public static Program parseProgram(String in) throws ParserException {
+	public static Program parseReplProgram(String in) throws ParserException {
 		var parser = new Parser(in);
-		return parser.parseProgram();
+		return parser.parseReplProgram();
 	}
 
 	private final PeekableStream<Token> input;
@@ -59,6 +59,15 @@ public class Parser {
 		return new Program(Collections.unmodifiableList(statements));
 	}
 
+	public Program parseReplProgram() throws ParserException {
+		var statements = new ArrayList<Statement>();
+		while (!maybeConsumeToken(Token.Type.EOF)) {
+			statements.add(parseReplLine());
+			maybeConsumeToken(Token.Type.SEMICOLON);
+		}
+		return new Program(Collections.unmodifiableList(statements));
+	}
+
 	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
@@ -275,6 +284,14 @@ public class Parser {
 		return new LetInExpression(Collections.unmodifiableList(bindings), body);
 	}
 
+	private Statement parseReplLine() throws ParserException {
+		if (input.peek().type() == Token.Type.DEF) {
+			return parseStatement();
+		} else {
+			return new ExpressionStatement(parseExpression());
+		}
+	}
+
 	private Expression parseSimpleExpression() throws ParserException {
 		return switch (input.peek().type()) {
 			case PAREN_LEFT -> {
@@ -307,11 +324,7 @@ public class Parser {
 	}
 
 	private Statement parseStatement() throws ParserException {
-		if (input.peek().type() == Token.Type.DEF) {
-			return parseDefinition();
-		} else {
-			return new ExpressionStatement(parseExpression());
-		}
+		return parseDefinition();
 	}
 
 	private Expression parseString() throws ParserException {
-- 
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