From 928b391e3d6fe343351d15c5fb24c338bac57818 Mon Sep 17 00:00:00 2001
From: Ben Bridle <ben@derelict.engineering>
Date: Wed, 15 Oct 2025 11:28:29 +1300
Subject: Add debug operator for expressions

The <dbg> operator will print the value that is currently at the top of
the expression stack as an info-level log message, to help with
debugging complex expressions.
---
 src/types/expression_stack.rs | 14 ++++++++++++++
 src/types/operator.rs         |  3 +++
 2 files changed, 17 insertions(+)

diff --git a/src/types/expression_stack.rs b/src/types/expression_stack.rs
index 25710d2..3f80dc8 100644
--- a/src/types/expression_stack.rs
+++ b/src/types/expression_stack.rs
@@ -70,6 +70,7 @@ impl ExpressionStack {
             Operator::Length           => {          pop!(a); push!(op_length(a)) },
             Operator::Sum              => {          pop!(a); push!(op_sum(a)) },
             Operator::Absolute         => {          pop!(a); push!(op_absolute(a)) },
+            Operator::Debug            => {          pop!(a); op_debug(&a, &source); push!(Ok(a)) },
         }
         return Ok(());
     }
@@ -184,6 +185,19 @@ fn op_sum(l: IntermediateValue) -> Result<IntermediateValue, ExpressionError> {
 }
 fn op_absolute(l: IntermediateValue) -> Result<IntermediateValue, ExpressionError> {
     Ok(from_isize(to_isize(l)?.wrapping_abs()))  }
+fn op_debug(l: &IntermediateValue, source: &SourceSpan) {
+    let (type_name, value) = match l {
+        IntermediateValue::Integer(integer) =>
+            ("integer", integer.to_string()),
+        IntermediateValue::List(list) => {
+            let strings: Vec<String> = list.iter().map(|t| t.value.to_string()).collect();
+            ("list", format!("[{}]", strings.join(" ")))
+        }
+        IntermediateValue::Block(_) => unreachable!("Block value in expression"),
+    };
+    let message = format!("Printing {type_name} value in expression at {}", source.location());
+    log_info(&message, Some(format!("    --> {value}\n")));
+}
 
 
 /// Find the number of bits required to hold an integer.
diff --git a/src/types/operator.rs b/src/types/operator.rs
index e360567..8a76e52 100644
--- a/src/types/operator.rs
+++ b/src/types/operator.rs
@@ -21,6 +21,7 @@ pub enum Operator {
     Length,
     Sum,
     Absolute,
+    Debug,
 }
 
 impl Operator {
@@ -61,6 +62,7 @@ impl Operator {
             "<len>" => Some(Operator::Length),
             "<sum>" => Some(Operator::Sum),
             "<abs>" => Some(Operator::Absolute),
+            "<dbg>" => Some(Operator::Debug),
             _       => None,
         }
     }
@@ -90,6 +92,7 @@ impl std::fmt::Display for Operator {
             Operator::Length           => "<len>",
             Operator::Sum              => "<sum>",
             Operator::Absolute         => "<abs>",
+            Operator::Debug            => "<dbg>",
         };
         write!(f, "{string}")
     }
-- 
cgit v1.2.3-70-g09d2