diff --git a/mers_lib/src/data/function.rs b/mers_lib/src/data/function.rs
index 0c98a1f..e63e69f 100755
--- a/mers_lib/src/data/function.rs
+++ b/mers_lib/src/data/function.rs
@@ -133,6 +133,11 @@ impl Display for Function {
 }
 impl Display for FunctionT {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        write!(f, "Function")
+        match (self.0)(&Type::empty_tuple()) {
+            Ok(t) => write!(f, "Function /* () -> {t} */"),
+            Err(_) => {
+                write!(f, "Function",)
+            }
+        }
     }
 }
diff --git a/mers_lib/src/program/run/mod.rs b/mers_lib/src/program/run/mod.rs
index 611a723..4253392 100755
--- a/mers_lib/src/program/run/mod.rs
+++ b/mers_lib/src/program/run/mod.rs
@@ -90,7 +90,7 @@ pub struct CheckErrorHRConfig {
 }
 pub struct CheckErrorDisplay<'a> {
     e: &'a CheckError,
-    src: &'a Source,
+    src: Option<&'a Source>,
 }
 impl Display for CheckErrorDisplay<'_> {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
@@ -123,13 +123,19 @@ impl CheckError {
         self.add(CheckErrorComponent::Source(s))
     }
     pub fn display<'a>(&'a self, src: &'a Source) -> CheckErrorDisplay<'a> {
-        CheckErrorDisplay { e: self, src }
+        CheckErrorDisplay {
+            e: self,
+            src: Some(src),
+        }
+    }
+    pub fn display_no_src<'a>(&'a self) -> CheckErrorDisplay<'a> {
+        CheckErrorDisplay { e: self, src: None }
     }
     // will, unless empty, end in a newline
     fn human_readable(
         &self,
         f: &mut std::fmt::Formatter<'_>,
-        src: &Source,
+        src: Option<&Source>,
         cfg: &CheckErrorHRConfig,
     ) -> std::fmt::Result {
         let len = self.0.len();
@@ -155,50 +161,55 @@ impl CheckError {
                     err.human_readable(f, src, &cfg)?;
                 }
                 CheckErrorComponent::Source(highlights) => {
-                    let start = highlights.iter().map(|v| v.0.start.pos()).min();
-                    let end = highlights.iter().map(|v| v.0.start.pos()).max();
-                    if let (Some(start), Some(end)) = (start, end) {
-                        writeln!(f, "{}Line(s) [?] ({start}..{end})", indent!())?;
-                        let start = src.get_line_start(start);
-                        let end = src.get_line_end(end);
-                        let lines = src.src()[start..end].line_spans().collect::<Vec<_>>();
-                        for line in lines {
-                            let line_start = line.start();
-                            let line_end = line.end();
-                            let line = line.as_str();
-                            writeln!(f, "{} {line}", indent!())?;
-                            let mut right = 0;
-                            for (pos, color) in highlights {
-                                if let Some(color) = color {
-                                    let highlight_start = pos.start.pos() - start;
-                                    let highlight_end = pos.end.pos() - start;
-                                    if highlight_start < line_end && highlight_end > line_start {
-                                        let hl_start = highlight_start.saturating_sub(line_start);
-                                        if hl_start < right {
-                                            right = 0;
-                                            writeln!(f)?;
+                    if let Some(src) = src {
+                        let start = highlights.iter().map(|v| v.0.start.pos()).min();
+                        let end = highlights.iter().map(|v| v.0.start.pos()).max();
+                        if let (Some(start), Some(end)) = (start, end) {
+                            writeln!(f, "{}Line(s) [?] ({start}..{end})", indent!())?;
+                            let start = src.get_line_start(start);
+                            let end = src.get_line_end(end);
+                            let lines = src.src()[start..end].line_spans().collect::<Vec<_>>();
+                            for line in lines {
+                                let line_start = line.start();
+                                let line_end = line.end();
+                                let line = line.as_str();
+                                writeln!(f, "{} {line}", indent!())?;
+                                let mut right = 0;
+                                for (pos, color) in highlights {
+                                    if let Some(color) = color {
+                                        let highlight_start = pos.start.pos() - start;
+                                        let highlight_end = pos.end.pos() - start;
+                                        if highlight_start < line_end && highlight_end > line_start
+                                        {
+                                            let hl_start =
+                                                highlight_start.saturating_sub(line_start);
+                                            if hl_start < right {
+                                                right = 0;
+                                                writeln!(f)?;
+                                            }
+                                            let hl_len = highlight_end
+                                                .saturating_sub(line_start)
+                                                .saturating_sub(hl_start);
+                                            let hl_space = hl_start - right;
+                                            let print_indent = right == 0;
+                                            right += hl_space + hl_len;
+                                            let hl_len =
+                                                hl_len.min(highlight_end - highlight_start);
+                                            if print_indent && right != 0 {
+                                                write!(f, "{} ", indent!())?;
+                                            }
+                                            write!(
+                                                f,
+                                                "{}{}",
+                                                " ".repeat(hl_space),
+                                                "^".repeat(hl_len).color(*color)
+                                            )?;
                                         }
-                                        let hl_len = highlight_end
-                                            .saturating_sub(line_start)
-                                            .saturating_sub(hl_start);
-                                        let hl_space = hl_start - right;
-                                        let print_indent = right == 0;
-                                        right += hl_space + hl_len;
-                                        let hl_len = hl_len.min(highlight_end - highlight_start);
-                                        if print_indent && right != 0 {
-                                            write!(f, "{} ", indent!())?;
-                                        }
-                                        write!(
-                                            f,
-                                            "{}{}",
-                                            " ".repeat(hl_space),
-                                            "^".repeat(hl_len).color(*color)
-                                        )?;
                                     }
                                 }
-                            }
-                            if right != 0 {
-                                writeln!(f)?;
+                                if right != 0 {
+                                    writeln!(f)?;
+                                }
                             }
                         }
                     }