Add proper description of function type

1 files changed, 37 insertions, 2 deletions

diff --git a/src/main/java/org/shedlang/compiler/types/FunctionType.java b/src/main/java/org/shedlang/compiler/types/FunctionType.java
index e40439f7..c52de92e 100644
--- a/src/main/java/org/shedlang/compiler/types/FunctionType.java
+++ b/src/main/java/org/shedlang/compiler/types/FunctionType.java
@@ -5,6 +5,8 @@ import org.pcollections.PVector;
 
 import java.util.List;
 
+import static org.shedlang.compiler.util.Iterables.forEachInterspersed;
+
 public record FunctionType(
     List<Type> positionalParams,
     List<NamedParam> namedParams,
@@ -17,8 +19,41 @@ public record FunctionType(
 
     @Override
     public String describe() {
-        // TODO: implement this sensibly
-        return toString();
+        var description = new StringBuilder();
+        description.append("fn (");
+
+        forEachInterspersed(
+            positionalParams,
+            param -> description.append(param.describe()),
+            () -> description.append(", ")
+        );
+
+        if (!positionalParams.isEmpty() && !namedParams.isEmpty()) {
+            description.append(", ");
+        }
+
+        forEachInterspersed(
+            namedParams,
+            param -> {
+                description.append(".");
+                description.append(param.name());
+                description.append(": ");
+                description.append(param.type().describe());
+            },
+            () -> description.append(", ")
+        );
+
+        description.append(")");
+
+        if (!effect.equals(Effects.NONE)) {
+            description.append(" ! ");
+            description.append(effect.describe());
+        }
+
+        description.append(" -> ");
+        description.append(returnType.describe());
+
+        return description.toString();
     }
 
     public record Builder(