diff --git a/app/src/main/java/org/solovyev/android/calculator/BaseDialogFragment.java b/app/src/main/java/org/solovyev/android/calculator/BaseDialogFragment.java
index 118df5c7..8d4223ad 100644
--- a/app/src/main/java/org/solovyev/android/calculator/BaseDialogFragment.java
+++ b/app/src/main/java/org/solovyev/android/calculator/BaseDialogFragment.java
@@ -1,6 +1,7 @@
 package org.solovyev.android.calculator;
 
 import android.content.Context;
+import android.content.DialogInterface;
 import android.content.SharedPreferences;
 import android.os.Bundle;
 import android.support.annotation.NonNull;
@@ -11,6 +12,8 @@ import android.support.v4.app.FragmentActivity;
 import android.support.v7.app.AlertDialog;
 import android.view.LayoutInflater;
 import android.view.View;
+import android.view.Window;
+import android.view.WindowManager;
 import android.view.inputmethod.InputMethodManager;
 
 import javax.inject.Inject;
@@ -41,7 +44,17 @@ public abstract class BaseDialogFragment extends DialogFragment {
         final AlertDialog.Builder b = new AlertDialog.Builder(context, theme.alertDialogTheme);
         b.setView(view, spacing, spacing, spacing, spacing);
         onPrepareDialog(b);
-        return b.create();
+        final AlertDialog dialog = b.create();
+        dialog.setOnShowListener(new DialogInterface.OnShowListener() {
+            @Override
+            public void onShow(DialogInterface d) {
+                onShowDialog(dialog);
+            }
+        });
+        return dialog;
+    }
+
+    protected void onShowDialog(@NonNull AlertDialog dialog) {
     }
 
     protected abstract void onPrepareDialog(@NonNull AlertDialog.Builder builder);
diff --git a/app/src/main/java/org/solovyev/android/calculator/KeyboardUi.java b/app/src/main/java/org/solovyev/android/calculator/KeyboardUi.java
index 3c387b00..7f872aef 100644
--- a/app/src/main/java/org/solovyev/android/calculator/KeyboardUi.java
+++ b/app/src/main/java/org/solovyev/android/calculator/KeyboardUi.java
@@ -6,6 +6,7 @@ import android.content.res.Resources;
 import android.graphics.Color;
 import android.graphics.PointF;
 import android.os.Build;
+import android.support.annotation.ColorInt;
 import android.support.annotation.DrawableRes;
 import android.support.annotation.IdRes;
 import android.support.annotation.NonNull;
@@ -42,9 +43,13 @@ public class KeyboardUi {
     private final List<String> parameterNames;
     @NonNull
     private final SimpleDragListener dragListener;
+    @ColorInt
     private final int textColor;
+    @ColorInt
     private final int textColorSecondary;
     private final int sidePadding;
+    @DrawableRes
+    private final int buttonBackground;
 
     @SuppressWarnings("deprecation")
     public KeyboardUi(@NonNull User user, @NonNull List<String> parameterNames) {
@@ -55,6 +60,7 @@ public class KeyboardUi {
         textColor = resources.getColor(R.color.cpp_button_text);
         textColorSecondary = resources.getColor(R.color.cpp_button_text);
         sidePadding = resources.getDimensionPixelSize(R.dimen.cpp_button_padding);
+        buttonBackground = App.getTheme().light ? R.drawable.material_button_light : R.drawable.material_button_dark;
     }
 
     public void makeView() {
@@ -148,7 +154,7 @@ public class KeyboardUi {
     private void fillButton(@NonNull View button, @IdRes int id) {
         button.setOnClickListener(buttonHandler);
         button.setId(id);
-        button.setBackgroundResource(R.drawable.material_button_light);
+        button.setBackgroundResource(buttonBackground);
         button.setPadding(sidePadding, 1, sidePadding, 1);
         if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
             button.setStateListAnimator(null);
diff --git a/app/src/main/java/org/solovyev/android/calculator/KeyboardWindow.java b/app/src/main/java/org/solovyev/android/calculator/KeyboardWindow.java
index a17d5632..eb8178f5 100644
--- a/app/src/main/java/org/solovyev/android/calculator/KeyboardWindow.java
+++ b/app/src/main/java/org/solovyev/android/calculator/KeyboardWindow.java
@@ -53,7 +53,7 @@ public class KeyboardWindow {
         final Context context = editor.getContext();
         final LinearLayout view = new LinearLayout(context);
         view.setOrientation(LinearLayout.VERTICAL);
-        final int buttonSize = context.getResources().getDimensionPixelSize(R.dimen.cpp_kb_button_size);
+        final int buttonSize = context.getResources().getDimensionPixelSize(R.dimen.cpp_clickable_area_size);
         final int keyboardSize = 5 * buttonSize;
         window = new PopupWindow(view, keyboardSize, keyboardSize);
         window.setClippingEnabled(false);
@@ -98,6 +98,9 @@ public class KeyboardWindow {
             return;
         }
         final Window window = dialog.getWindow();
+        if (window == null) {
+            return;
+        }
         final WindowManager.LayoutParams lp = window.getAttributes();
         lp.gravity = gravity;
         window.setAttributes(lp);
diff --git a/app/src/main/java/org/solovyev/android/calculator/function/CppFunction.java b/app/src/main/java/org/solovyev/android/calculator/function/CppFunction.java
index dbb3f5aa..f46b4e3b 100644
--- a/app/src/main/java/org/solovyev/android/calculator/function/CppFunction.java
+++ b/app/src/main/java/org/solovyev/android/calculator/function/CppFunction.java
@@ -47,9 +47,9 @@ public class CppFunction implements Jsonable, Parcelable {
     private static final String JSON_BODY = "b";
     private static final String JSON_PARAMETERS = "ps";
     private static final String JSON_DESCRIPTION = "d";
-    protected final int id;
     @Nonnull
     protected final List<String> parameters = new ArrayList<>();
+    protected int id;
     @Nonnull
     protected String name;
     @Nonnull
@@ -230,6 +230,13 @@ public class CppFunction implements Jsonable, Parcelable {
             return this;
         }
 
+        @Nonnull
+        public Builder withId(int id) {
+            Check.isTrue(!built);
+            function.id = id;
+            return this;
+        }
+
         @Nonnull
         public CppFunction build() {
             built = true;
diff --git a/app/src/main/java/org/solovyev/android/calculator/function/EditFunctionFragment.java b/app/src/main/java/org/solovyev/android/calculator/function/EditFunctionFragment.java
index 177c50cf..0c067dd4 100644
--- a/app/src/main/java/org/solovyev/android/calculator/function/EditFunctionFragment.java
+++ b/app/src/main/java/org/solovyev/android/calculator/function/EditFunctionFragment.java
@@ -43,10 +43,12 @@ import android.view.Menu;
 import android.view.MenuItem;
 import android.view.View;
 import android.view.ViewGroup;
+import android.view.ViewParent;
 import android.view.inputmethod.InputMethodManager;
 import android.widget.Button;
 import android.widget.EditText;
 
+import org.solovyev.android.Check;
 import org.solovyev.android.calculator.App;
 import org.solovyev.android.calculator.AppComponent;
 import org.solovyev.android.calculator.BaseDialogFragment;
@@ -62,8 +64,11 @@ import org.solovyev.android.calculator.math.edit.FunctionsFragment;
 import org.solovyev.android.calculator.math.edit.VarEditorSaver;
 import org.solovyev.common.math.MathRegistry;
 
+import java.util.ArrayList;
 import java.util.Collections;
+import java.util.HashSet;
 import java.util.List;
+import java.util.Set;
 
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
@@ -75,6 +80,8 @@ import jscl.math.function.CustomFunction;
 import jscl.math.function.Function;
 import jscl.math.function.IConstant;
 
+import static org.solovyev.android.calculator.function.CppFunction.NO_ID;
+
 public class EditFunctionFragment extends BaseDialogFragment implements View.OnClickListener, View.OnFocusChangeListener, View.OnKeyListener {
 
     private static final String ARG_FUNCTION = "function";
@@ -101,12 +108,12 @@ public class EditFunctionFragment extends BaseDialogFragment implements View.OnC
     EditText bodyView;
     @Bind(R.id.function_description)
     EditText descriptionView;
-    private CppFunction function;
-
     @Inject
     Calculator calculator;
     @Inject
     FunctionsRegistry registry;
+    @Nullable
+    private CppFunction function;
 
     @Nonnull
     private static EditFunctionFragment create(@Nullable CppFunction function) {
@@ -141,7 +148,10 @@ public class EditFunctionFragment extends BaseDialogFragment implements View.OnC
     @Override
     public void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
-        function = getArguments().getParcelable(ARG_FUNCTION);
+        final Bundle arguments = getArguments();
+        if (arguments != null) {
+            function = arguments.getParcelable(ARG_FUNCTION);
+        }
     }
 
     @Override
@@ -165,31 +175,32 @@ public class EditFunctionFragment extends BaseDialogFragment implements View.OnC
     public AlertDialog onCreateDialog(Bundle savedInstanceState) {
         final AlertDialog dialog = super.onCreateDialog(savedInstanceState);
         dialog.setCanceledOnTouchOutside(false);
-        dialog.setOnShowListener(new DialogInterface.OnShowListener() {
-            @Override
-            public void onShow(DialogInterface d) {
-                nameView.selectAll();
-                showIme(nameView);
+        return dialog;
+    }
 
-                final Button ok = dialog.getButton(AlertDialog.BUTTON_POSITIVE);
-                ok.setOnClickListener(new View.OnClickListener() {
-                    @Override
-                    public void onClick(View v) {
-                        tryClose();
-                    }
-                });
-                if (function != null) {
-                    final Button neutral = dialog.getButton(AlertDialog.BUTTON_NEUTRAL);
-                    neutral.setOnClickListener(new View.OnClickListener() {
-                        @Override
-                        public void onClick(View v) {
-                            tryRemoveFunction(function, false);
-                        }
-                    });
-                }
+    @Override
+    protected void onShowDialog(@NonNull AlertDialog dialog) {
+        super.onShowDialog(dialog);
+
+        nameView.selectAll();
+        showIme(nameView);
+
+        final Button ok = dialog.getButton(AlertDialog.BUTTON_POSITIVE);
+        ok.setOnClickListener(new View.OnClickListener() {
+            @Override
+            public void onClick(View v) {
+                tryClose();
             }
         });
-        return dialog;
+        if (function != null) {
+            final Button neutral = dialog.getButton(AlertDialog.BUTTON_NEUTRAL);
+            neutral.setOnClickListener(new View.OnClickListener() {
+                @Override
+                public void onClick(View v) {
+                    tryRemoveFunction(function, false);
+                }
+            });
+        }
     }
 
     private void tryRemoveFunction(@NonNull CppFunction function, boolean confirmed) {
@@ -220,19 +231,58 @@ public class EditFunctionFragment extends BaseDialogFragment implements View.OnC
 
     @Override
     public void onFocusChange(View v, boolean hasFocus) {
-        if (v.getId() == R.id.function_body) {
-            if (hasFocus) {
-                keyboardWindow.show(keyboardUser, getDialog(), paramsView.getParams());
-            } else {
-                keyboardWindow.hide();
+        if (v instanceof EditText && FunctionParamsView.PARAM_VIEW_TAG.equals(v.getTag())) {
+            final ViewParent parentView = v.getParent();
+            if (parentView instanceof TextInputLayout) {
+                if (hasFocus) {
+                    clearError((TextInputLayout) parentView);
+                } else {
+                    validateParameters();
+                }
+            }
+            return;
+        }
+
+        final int id = v.getId();
+        switch (id) {
+            case R.id.function_name:
+                if (hasFocus) {
+                    clearError(nameLabel);
+                } else {
+                    validateName();
+                }
+                break;
+            case R.id.function_body:
+                if (hasFocus) {
+                    clearError(bodyLabel);
+                    showKeyboard();
+                } else {
+                    keyboardWindow.hide();
+                    validateBody();
+                }
+                break;
+        }
+    }
+
+    private void showKeyboard() {
+        keyboardWindow.show(keyboardUser, getDialog(), collectParameters());
+    }
+
+    @Nonnull
+    private List<String> collectParameters() {
+        final List<String> parameters = new ArrayList<>();
+        for (String parameter : paramsView.getParams()) {
+            if (!TextUtils.isEmpty(parameter)) {
+                parameters.add(parameter);
             }
         }
+        return parameters;
     }
 
     @Override
     public void onClick(View v) {
         if (v.getId() == R.id.function_body) {
-            keyboardWindow.show(keyboardUser, getDialog(), paramsView.getParams());
+            showKeyboard();
         }
     }
 
@@ -255,38 +305,16 @@ public class EditFunctionFragment extends BaseDialogFragment implements View.OnC
     }
 
     private void applyData() {
-
+        final CppFunction newFunction = CppFunction.builder(nameView.getText().toString(), bodyView.getText().toString())
+                .withId(function == null ? NO_ID : function.id)
+                .withParameters(collectParameters())
+                .withDescription(descriptionView.getText().toString()).build();
+        final Function oldFunction = (function == null || function.id == NO_ID) ? null : registry.getById(function.id);
+        registry.add(newFunction.toCustomFunctionBuilder(), oldFunction);
     }
 
     private boolean validate() {
-        if (!validateName()) {
-            return false;
-        }
-        if (!validateParameters()) {
-            return false;
-        }
-        if (!validateBody()) {
-            return false;
-        }
-
-        final CppFunction newFunction = CppFunction.builder(nameView.getText().toString(), bodyView.getText().toString())
-                .withParameters(paramsView.getParams())
-                .withDescription(descriptionView.getText().toString()).build();
-        final Function oldFunction = function.id == CppFunction.NO_ID ? null : registry.getById(function.id);
-        registry.add(newFunction.toCustomFunctionBuilder(), oldFunction);
-        return true;
-    }
-
-    private boolean validateParameters(@Nonnull List<String> parameterNames) {
-        for (String parameterName : parameterNames) {
-            if (!VarEditorSaver.isValidName(parameterName)) {
-                return false;
-            }
-        }
-        //                error = R.string.function_param_not_empty;
-
-
-        return true;
+        return validateName() & validateParameters() & validateBody();
     }
 
     private boolean validateName() {
@@ -296,9 +324,16 @@ public class EditFunctionFragment extends BaseDialogFragment implements View.OnC
             return false;
         }
         final Function existingFunction = registry.get(name);
-        if (existingFunction != null && (!existingFunction.isIdDefined() || !existingFunction.getId().equals(function.getId()))) {
-            setError(nameLabel, getString(R.string.function_already_exists));
-            return false;
+        if (existingFunction != null) {
+            if (!existingFunction.isIdDefined()) {
+                Check.shouldNotHappen();
+                setError(nameLabel, getString(R.string.function_already_exists));
+                return false;
+            }
+            if (function != null && !existingFunction.getId().equals(function.getId())) {
+                setError(nameLabel, getString(R.string.function_already_exists));
+                return false;
+            }
         }
         clearError(nameLabel);
         return true;
@@ -315,13 +350,26 @@ public class EditFunctionFragment extends BaseDialogFragment implements View.OnC
     }
 
     private boolean validateParameters() {
+        boolean valid = true;
         final List<String> parameters = paramsView.getParams();
-        /*if (TextUtils.isEmpty(body)) {
-            setError(bodyLabel, getString(R.string.function_is_empty));
-            return false;
-        }*/
-        //clearError(bodyLabel);
-        return true;
+        final Set<String> usedParameters = new HashSet<>();
+        for (int i = 0; i < parameters.size(); i++) {
+            final String parameter = parameters.get(i);
+            final TextInputLayout paramLabel = paramsView.getParamLabel(i);
+            if (TextUtils.isEmpty(parameter)) {
+                clearError(paramLabel);
+            } else if (!VarEditorSaver.isValidName(parameter)) {
+                valid = false;
+                setError(paramLabel, getString(R.string.invalid_name));
+            } else if (usedParameters.contains(parameter)) {
+                valid = false;
+                setError(paramLabel, getString(R.string.function_duplicate_parameter));
+            } else {
+                usedParameters.add(parameter);
+                clearError(paramLabel);
+            }
+        }
+        return valid;
     }
 
     @SuppressLint("InflateParams")
@@ -331,15 +379,18 @@ public class EditFunctionFragment extends BaseDialogFragment implements View.OnC
         final View view = inflater.inflate(R.layout.fragment_function_edit, null);
         ButterKnife.bind(this, view);
 
-        if (savedInstanceState == null) {
+        if (savedInstanceState == null && function != null) {
             paramsView.addParams(function.getParameters());
             nameView.setText(function.getName());
             descriptionView.setText(function.getDescription());
             bodyView.setText(function.getBody());
         }
+        nameView.setOnFocusChangeListener(this);
+        paramsView.setOnFocusChangeListener(this);
         bodyView.setOnClickListener(this);
         bodyView.setOnFocusChangeListener(this);
         bodyView.setOnKeyListener(this);
+        descriptionView.setOnFocusChangeListener(this);
 
         return view;
     }
diff --git a/app/src/main/java/org/solovyev/android/calculator/function/FunctionParamsView.java b/app/src/main/java/org/solovyev/android/calculator/function/FunctionParamsView.java
index f7aee1bb..fd4bfdc1 100644
--- a/app/src/main/java/org/solovyev/android/calculator/function/FunctionParamsView.java
+++ b/app/src/main/java/org/solovyev/android/calculator/function/FunctionParamsView.java
@@ -27,9 +27,9 @@ import android.content.Context;
 import android.os.Build;
 import android.os.Parcel;
 import android.os.Parcelable;
-import android.text.Editable;
-import android.text.TextUtils;
+import android.support.design.widget.TextInputLayout;
 import android.util.AttributeSet;
+import android.view.Gravity;
 import android.view.View;
 import android.view.ViewGroup;
 import android.view.inputmethod.EditorInfo;
@@ -53,9 +53,13 @@ import static android.view.ViewGroup.LayoutParams.WRAP_CONTENT;
 
 public class FunctionParamsView extends LinearLayout {
 
+    @Nonnull
+    public static final String PARAM_VIEW_TAG = "param-view";
+    private static final int HEADERS = 1;
     private static final int PARAM_VIEW_INDEX = 3;
     private static final int START_ROW_ID = App.generateViewId();
     private int maxRowId = START_ROW_ID;
+    private final int clickableAreaSize = getResources().getDimensionPixelSize(R.dimen.cpp_clickable_area_size);
 
     public FunctionParamsView(Context context) {
         super(context);
@@ -86,8 +90,8 @@ public class FunctionParamsView extends LinearLayout {
                 addParam(null);
             }
         });
-        headerView.addView(addButton, new LayoutParams(0, WRAP_CONTENT, 1));
-        headerView.addView(new View(context), new LayoutParams(0, WRAP_CONTENT, 5));
+        headerView.addView(addButton, new LayoutParams(clickableAreaSize, WRAP_CONTENT));
+        headerView.addView(new View(context), new LayoutParams(0, WRAP_CONTENT, 1));
         addView(headerView, new ViewGroup.LayoutParams(MATCH_PARENT, WRAP_CONTENT));
     }
 
@@ -95,10 +99,11 @@ public class FunctionParamsView extends LinearLayout {
     private LinearLayout makeRowView(@Nonnull Context context) {
         final LinearLayout rowView = new LinearLayout(context);
         rowView.setOrientation(HORIZONTAL);
+        rowView.setMinimumHeight(clickableAreaSize);
+        rowView.setGravity(Gravity.CENTER_VERTICAL);
         return rowView;
     }
 
-
     public void addParams(@Nonnull List<String> params) {
         for (String param : params) {
             addParam(param);
@@ -121,7 +126,7 @@ public class FunctionParamsView extends LinearLayout {
             }
         });
         removeButton.setText("−");
-        rowView.addView(removeButton, new LayoutParams(0, WRAP_CONTENT, 1));
+        rowView.addView(removeButton, new LayoutParams(clickableAreaSize, WRAP_CONTENT));
 
         final Button upButton = new Button(context);
         upButton.setOnClickListener(new OnClickListener() {
@@ -131,7 +136,7 @@ public class FunctionParamsView extends LinearLayout {
             }
         });
         upButton.setText("↑");
-        rowView.addView(upButton, new LayoutParams(0, WRAP_CONTENT, 1));
+        rowView.addView(upButton, new LayoutParams(clickableAreaSize, WRAP_CONTENT));
 
         final Button downButton = new Button(context);
         downButton.setOnClickListener(new OnClickListener() {
@@ -141,16 +146,21 @@ public class FunctionParamsView extends LinearLayout {
             }
         });
         downButton.setText("↓");
-        rowView.addView(downButton, new LayoutParams(0, WRAP_CONTENT, 1));
+        rowView.addView(downButton, new LayoutParams(clickableAreaSize, WRAP_CONTENT));
 
+        final TextInputLayout paramLabel = new TextInputLayout(context);
         final EditText paramView = new EditText(context);
         if (param != null) {
             paramView.setText(param);
         }
+        paramView.setOnFocusChangeListener(getOnFocusChangeListener());
         paramView.setInputType(EditorInfo.TYPE_CLASS_TEXT);
         paramView.setId(id);
+        paramView.setTag(PARAM_VIEW_TAG);
         paramView.setHint(R.string.c_function_parameter);
-        rowView.addView(paramView, new LayoutParams(0, WRAP_CONTENT, 3));
+        paramLabel.addView(paramView, new TextInputLayout.LayoutParams(MATCH_PARENT, WRAP_CONTENT));
+
+        rowView.addView(paramLabel, new LayoutParams(0, WRAP_CONTENT, 1));
 
         addView(rowView, new ViewGroup.LayoutParams(MATCH_PARENT, WRAP_CONTENT));
     }
@@ -158,20 +168,20 @@ public class FunctionParamsView extends LinearLayout {
     private void downRow(@Nonnull ViewGroup row) {
         final int index = indexOfChild(row);
         if (index < getChildCount() - 1) {
-            swap(row, getRowByIndex(index + 1));
+            swap(row, getRow(index + 1));
         }
     }
 
     private void upRow(@Nonnull ViewGroup row) {
         final int index = indexOfChild(row);
         if (index > 1) {
-            swap(row, getRowByIndex(index - 1));
+            swap(row, getRow(index - 1));
         }
     }
 
     private void swap(@Nonnull ViewGroup l, @Nonnull ViewGroup r) {
-        final EditText lParam = (EditText) l.getChildAt(PARAM_VIEW_INDEX);
-        final EditText rParam = (EditText) r.getChildAt(PARAM_VIEW_INDEX);
+        final EditText lParam = getParamView(l);
+        final EditText rParam = getParamView(r);
         swap(lParam, rParam);
     }
 
@@ -183,7 +193,7 @@ public class FunctionParamsView extends LinearLayout {
     }
 
     @Nonnull
-    private ViewGroup getRowByIndex(int index) {
+    private ViewGroup getRow(int index) {
         Check.isTrue(index >= 0 && index < getChildCount());
         return (ViewGroup) getChildAt(index);
     }
@@ -196,18 +206,26 @@ public class FunctionParamsView extends LinearLayout {
     public List<String> getParams() {
         final List<String> params = new ArrayList<>(getChildCount());
 
-        for (int i = 1; i < getChildCount(); i++) {
-            final ViewGroup row = getRowByIndex(i);
-            final EditText paramView = (EditText) row.getChildAt(PARAM_VIEW_INDEX);
-            final Editable param = paramView.getText();
-            if (!TextUtils.isEmpty(param)) {
-                params.add(param.toString());
-            }
+        for (int i = HEADERS; i < getChildCount(); i++) {
+            final ViewGroup row = getRow(i);
+            final EditText paramView = getParamView(row);
+            params.add(paramView.getText().toString());
         }
 
         return params;
     }
 
+    @Nonnull
+    private EditText getParamView(@Nonnull ViewGroup row) {
+        final TextInputLayout paramLabel = getParamLabel(row);
+        return (EditText) paramLabel.getChildAt(0);
+    }
+
+    @Nonnull
+    private TextInputLayout getParamLabel(@Nonnull ViewGroup row) {
+        return (TextInputLayout) row.getChildAt(PARAM_VIEW_INDEX);
+    }
+
     @Override
     protected Parcelable onSaveInstanceState() {
         final Parcelable superState = super.onSaveInstanceState();
@@ -218,9 +236,9 @@ public class FunctionParamsView extends LinearLayout {
     private int[] getRowIds() {
         final int childCount = getChildCount();
         final int[] rowIds = new int[childCount - 1];
-        for (int i = 1; i < childCount; i++) {
-            final ViewGroup row = getRowByIndex(i);
-            final EditText paramView = (EditText) row.getChildAt(PARAM_VIEW_INDEX);
+        for (int i = HEADERS; i < childCount; i++) {
+            final ViewGroup row = getRow(i);
+            final EditText paramView = getParamView(row);
             rowIds[i - 1] = paramView.getId();
         }
         return rowIds;
@@ -243,6 +261,11 @@ public class FunctionParamsView extends LinearLayout {
         super.onRestoreInstanceState(state.getSuperState());
     }
 
+    @Nonnull
+    public TextInputLayout getParamLabel(int param) {
+        return getParamLabel(getRow(param + HEADERS));
+    }
+
     public static final class SavedState extends BaseSavedState {
 
         public static final Parcelable.Creator<SavedState> CREATOR =
diff --git a/app/src/main/res/layout/fragment_function_edit.xml b/app/src/main/res/layout/fragment_function_edit.xml
index ec6db2ea..714ed30c 100644
--- a/app/src/main/res/layout/fragment_function_edit.xml
+++ b/app/src/main/res/layout/fragment_function_edit.xml
@@ -23,7 +23,7 @@
   -->
 
 <ScrollView xmlns:a="http://schemas.android.com/apk/res/android"
-    a:layout_width="match_parent"
+    a:layout_width="wrap_content"
     a:layout_height="wrap_content">
 
     <LinearLayout
@@ -47,7 +47,8 @@
         <org.solovyev.android.calculator.function.FunctionParamsView
             a:id="@+id/function_params"
             a:layout_width="match_parent"
-            a:layout_height="wrap_content" />
+            a:layout_height="wrap_content"
+            a:orientation="vertical" />
 
         <android.support.design.widget.TextInputLayout
             a:id="@+id/function_body_label"
diff --git a/app/src/main/res/values-small/dimens.xml b/app/src/main/res/values-small/dimens.xml
index c5d03b3e..955f7d3c 100644
--- a/app/src/main/res/values-small/dimens.xml
+++ b/app/src/main/res/values-small/dimens.xml
@@ -29,5 +29,5 @@
 
     <dimen name="cpp_display_text_size">20sp</dimen>
     <dimen name="cpp_display_text_size_mobile">20sp</dimen>
-    <dimen name="cpp_kb_button_size">40dp</dimen>
+    <dimen name="cpp_clickable_area_size">40dp</dimen>
 </resources>
\ No newline at end of file
diff --git a/app/src/main/res/values/dimens.xml b/app/src/main/res/values/dimens.xml
index 56d56c2e..5e53a389 100644
--- a/app/src/main/res/values/dimens.xml
+++ b/app/src/main/res/values/dimens.xml
@@ -39,5 +39,6 @@
     <dimen name="cpp_onscreen_main_padding">1dp</dimen>
 
     <dimen name="cpp_dialog_spacing">20dp</dimen>
-    <dimen name="cpp_kb_button_size">50dp</dimen>
+    <dimen name="cpp_clickable_area_size">50dp</dimen>
+    <dimen name="cpp_dialog_width_max">400dp</dimen>
 </resources>
\ No newline at end of file
diff --git a/app/src/main/res/values/text_strings.xml b/app/src/main/res/values/text_strings.xml
index d5bf268c..3e01574d 100644
--- a/app/src/main/res/values/text_strings.xml
+++ b/app/src/main/res/values/text_strings.xml
@@ -155,7 +155,8 @@
     <string name="function_name_is_not_valid">Name of function is not valid: name must start with a letter, can contain letters, digits and underscore.</string>
     <string name="function_already_exists">Function with the same name already exists!</string>
     <string name="function_is_empty">Function body could not be empty!</string>
-    <string name="function_param_not_empty">Function parameter should not be empty!</string>
+    <string name="invalid_name">Invalid name</string>
+    <string name="function_duplicate_parameter">There is already a parameter with the same name</string>
     <string name="function_removal_confirmation_question">Do you really want to delete \'%s\' function?</string>
     <string name="empty_function_error">Unable to create empty function!</string>
     <string name="do_not_show_messages_in_session">Do not show this message until next session</string>