From 9932aa7ef1fb4812ff0496edbf2b0355813d53c3 Mon Sep 17 00:00:00 2001
From: Camden Dixie O'Brien <cdo@wip.sh>
Date: Thu, 24 Oct 2024 20:01:45 +0100
Subject: [PATCH] Make + and - left-associative

---
 lib/reader.c         | 60 ++++++++++++++++++++++----------------------
 tests/reader_tests.c | 24 +++++++++---------
 2 files changed, 42 insertions(+), 42 deletions(-)

diff --git a/lib/reader.c b/lib/reader.c
index 0c6cfc8..5e94282 100644
--- a/lib/reader.c
+++ b/lib/reader.c
@@ -29,40 +29,40 @@ static int parse_expression(
 {
 	int result, used = 0;
 
-	expression_t *number;
-	result = parse_number(pool, input, len, &number);
-	if (0 >= result)
-		return 0;
-	used += result;
-	if (used >= len) {
-		*out = number;
-		return used;
-	}
-
-	operator_t operator;
-	switch (input[used]) {
-	case '+':
-		operator= OPERATOR_ADD;
-		break;
-	case '-':
-		operator= OPERATOR_SUBTRACT;
-		break;
-	default:
-		return 0;
-	}
-	++used;
-
-	expression_t *subexpr;
-	result = parse_expression(pool, input + used, len - used, &subexpr);
+	expression_t *expr;
+	result = parse_number(pool, input, len, &expr);
 	if (0 >= result)
 		return 0;
 	used += result;
 
-	expression_t *expr = allocate_expression(pool);
-	expr->is_number = false;
-	expr->application.operator= operator;
-	expr->application.operands[0] = number;
-	expr->application.operands[1] = subexpr;
+	while (len > used) {
+		const expression_t *term0 = expr;
+
+		operator_t operator;
+		switch (input[used]) {
+		case '+':
+			operator= OPERATOR_ADD;
+			break;
+		case '-':
+			operator= OPERATOR_SUBTRACT;
+			break;
+		default:
+			return 0;
+		}
+		++used;
+
+		expression_t *term1;
+		result = parse_number(pool, input + used, len - used, &term1);
+		if (0 >= result)
+			return 0;
+		used += result;
+
+		expr = allocate_expression(pool);
+		expr->is_number = false;
+		expr->application.operator= operator;
+		expr->application.operands[0] = term0;
+		expr->application.operands[1] = term1;
+	}
 
 	*out = expr;
 	return used;
diff --git a/tests/reader_tests.c b/tests/reader_tests.c
index 344c998..36ab9f5 100644
--- a/tests/reader_tests.c
+++ b/tests/reader_tests.c
@@ -64,7 +64,7 @@ input_6_minus_2_with_no_spaces_is_read_as_a_subtract_application(void)
 }
 
 static void
-input_1_plus_2_plus_3_is_parsed_as_a_right_nested_application(void)
+input_1_plus_2_plus_3_is_parsed_as_a_left_nested_application(void)
 {
 	init_memory_pool(&pool);
 	const expression_t *result = read_expression(&pool, "1+2+3", 5);
@@ -74,19 +74,19 @@ input_1_plus_2_plus_3_is_parsed_as_a_right_nested_application(void)
 
 	const expression_t *operand0 = result->application.operands[0];
 	ASSERT_NOT_NULL(operand0);
-	ASSERT_TRUE(operand0->is_number);
-	ASSERT_EQUAL(1, operand0->number);
+	ASSERT_FALSE(operand0->is_number);
+	ASSERT_EQUAL(OPERATOR_ADD, operand0->application.operator);
+	ASSERT_NOT_NULL(operand0->application.operands[0]);
+	ASSERT_TRUE(operand0->application.operands[0]->is_number);
+	ASSERT_EQUAL(1, operand0->application.operands[0]->number);
+	ASSERT_NOT_NULL(operand0->application.operands[1]);
+	ASSERT_TRUE(operand0->application.operands[1]->is_number);
+	ASSERT_EQUAL(2, operand0->application.operands[1]->number);
 
 	const expression_t *operand1 = result->application.operands[1];
 	ASSERT_NOT_NULL(operand1);
-	ASSERT_FALSE(operand1->is_number);
-	ASSERT_EQUAL(OPERATOR_ADD, operand1->application.operator);
-	ASSERT_NOT_NULL(operand1->application.operands[0]);
-	ASSERT_TRUE(operand1->application.operands[0]->is_number);
-	ASSERT_EQUAL(2, operand1->application.operands[0]->number);
-	ASSERT_NOT_NULL(operand1->application.operands[1]);
-	ASSERT_TRUE(operand1->application.operands[1]->is_number);
-	ASSERT_EQUAL(3, operand1->application.operands[1]->number);
+	ASSERT_TRUE(operand1->is_number);
+	ASSERT_EQUAL(3, operand1->number);
 }
 
 int main(void)
@@ -99,6 +99,6 @@ int main(void)
 	RUN_TEST(input_1_plus_2_with_no_spaces_is_read_as_an_add_application);
 	RUN_TEST(
 	    input_6_minus_2_with_no_spaces_is_read_as_a_subtract_application);
-	RUN_TEST(input_1_plus_2_plus_3_is_parsed_as_a_right_nested_application);
+	RUN_TEST(input_1_plus_2_plus_3_is_parsed_as_a_left_nested_application);
 	TESTING_END();
 }