Extract EnvironmentBuilder

3 files changed, 43 insertions, 16 deletions

diff --git a/src/main/java/org/shedlang/compiler/ast/typed/TypedParamsNode.java b/src/main/java/org/shedlang/compiler/ast/typed/TypedParamsNode.java
index f2601644..f7273497 100644
--- a/src/main/java/org/shedlang/compiler/ast/typed/TypedParamsNode.java
+++ b/src/main/java/org/shedlang/compiler/ast/typed/TypedParamsNode.java
@@ -3,6 +3,7 @@ package org.shedlang.compiler.ast.typed;
 import org.shedlang.compiler.sources.Source;
 
 import java.util.List;
+import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
 public record TypedParamsNode(
@@ -10,7 +11,8 @@ public record TypedParamsNode(
     List<TypedParamNode> named,
     Source source
 ) implements TypedNode {
-    public Stream<TypedParamNode> all() {
-        return Stream.concat(positional.stream(), named.stream());
+    public Iterable<TypedParamNode> all() {
+        return Stream.concat(positional.stream(), named.stream())
+            .collect(Collectors.toList());
     }
 }
diff --git a/src/main/java/org/shedlang/compiler/typechecker/EnvironmentBuilder.java b/src/main/java/org/shedlang/compiler/typechecker/EnvironmentBuilder.java
new file mode 100644
index 00000000..4ac46d2a
--- /dev/null
+++ b/src/main/java/org/shedlang/compiler/typechecker/EnvironmentBuilder.java
@@ -0,0 +1,27 @@
+package org.shedlang.compiler.typechecker;
+
+import org.pcollections.Empty;
+import org.pcollections.PMap;
+import org.shedlang.compiler.sources.Source;
+import org.shedlang.compiler.typechecker.errors.DuplicateVariableName;
+
+public class EnvironmentBuilder {
+    public static final EnvironmentBuilder EMPTY = new EnvironmentBuilder(Empty.map());
+
+    private PMap<String, TypeCheckerContext.Variable> environment;
+
+    private EnvironmentBuilder(PMap<String, TypeCheckerContext.Variable> environment) {
+        this.environment = environment;
+    }
+
+    public EnvironmentBuilder add(String name, TypeCheckerContext.Variable variable, Source source) {
+        if (environment.containsKey(name)) {
+            throw new DuplicateVariableName(name, source);
+        }
+        return new EnvironmentBuilder(environment.plus(name, variable));
+    }
+
+    public PMap<String, TypeCheckerContext.Variable> build() {
+        return environment;
+    }
+}
diff --git a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
index bf09b84b..e7688898 100644
--- a/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
+++ b/src/main/java/org/shedlang/compiler/typechecker/TypeChecker.java
@@ -259,30 +259,28 @@ public class TypeChecker {
 
         var typedReturnType = typeCheckTypeLevelExpression(TypeSets.META_TYPE, untyped.returnType(), context);
 
+        var bodyEnvironment = EnvironmentBuilder.EMPTY;
         // TODO: check for duplicate param names
-        var bodyEnvironment = typedParams.all()
-            .map(param -> Map.entry(
+
+        for (var param : typedParams.all()) {
+            bodyEnvironment = bodyEnvironment.add(
                 param.name(),
-                TypeCheckerContext.defined(param.type().value())
-            ))
-            .collect(PCollectors.toMap());
+                TypeCheckerContext.defined(param.type().value()),
+                param.source()
+            );
+        }
 
         for (var statement : untyped.body()) {
             for (var targetVariable : targetVariables(statement)) {
-                if (bodyEnvironment.containsKey(targetVariable.name())) {
-                    throw new DuplicateVariableName(
-                        targetVariable.name(),
-                        targetVariable.source()
-                    );
-                }
-                bodyEnvironment = bodyEnvironment.plus(
+                bodyEnvironment = bodyEnvironment.add(
                     targetVariable.name(),
-                    TypeCheckerContext.undefined()
+                    TypeCheckerContext.undefined(),
+                    targetVariable.source()
                 );
             }
         }
 
-        var bodyContext = context.enterFunction(bodyEnvironment, typedEffect.map(e -> e.value()).orElse(Effects.NONE));
+        var bodyContext = context.enterFunction(bodyEnvironment.build(), typedEffect.map(e -> e.value()).orElse(Effects.NONE));
 
         var bodyResult = bodyContext.mapWithContext(
             untyped.body(),