diff --git a/crates/nu-command/src/core_commands/export_def.rs b/crates/nu-command/src/core_commands/export_def.rs
new file mode 100644
index 000000000..b82418c48
--- /dev/null
+++ b/crates/nu-command/src/core_commands/export_def.rs
@@ -0,0 +1,35 @@
+use nu_protocol::ast::Call;
+use nu_protocol::engine::{Command, EvaluationContext};
+use nu_protocol::{Signature, SyntaxShape, Value};
+
+pub struct ExportDef;
+
+impl Command for ExportDef {
+    fn name(&self) -> &str {
+        "export def"
+    }
+
+    fn usage(&self) -> &str {
+        "Define a custom command and export it from a module"
+    }
+
+    fn signature(&self) -> nu_protocol::Signature {
+        Signature::build("export def")
+            .required("target", SyntaxShape::String, "definition name")
+            .required("params", SyntaxShape::Signature, "parameters")
+            .required(
+                "block",
+                SyntaxShape::Block(Some(vec![])),
+                "body of the definition",
+            )
+    }
+
+    fn run(
+        &self,
+        _context: &EvaluationContext,
+        call: &Call,
+        _input: Value,
+    ) -> Result<nu_protocol::Value, nu_protocol::ShellError> {
+        Ok(Value::Nothing { span: call.head })
+    }
+}
diff --git a/crates/nu-command/src/core_commands/hide.rs b/crates/nu-command/src/core_commands/hide.rs
new file mode 100644
index 000000000..9c9d611e1
--- /dev/null
+++ b/crates/nu-command/src/core_commands/hide.rs
@@ -0,0 +1,28 @@
+use nu_protocol::ast::Call;
+use nu_protocol::engine::{Command, EvaluationContext};
+use nu_protocol::{Signature, SyntaxShape, Value};
+
+pub struct Hide;
+
+impl Command for Hide {
+    fn name(&self) -> &str {
+        "hide"
+    }
+
+    fn usage(&self) -> &str {
+        "Hide definitions in the current scope"
+    }
+
+    fn signature(&self) -> nu_protocol::Signature {
+        Signature::build("hide").required("pattern", SyntaxShape::String, "import pattern")
+    }
+
+    fn run(
+        &self,
+        _context: &EvaluationContext,
+        call: &Call,
+        _input: Value,
+    ) -> Result<nu_protocol::Value, nu_protocol::ShellError> {
+        Ok(Value::Nothing { span: call.head })
+    }
+}
diff --git a/crates/nu-command/src/core_commands/mod.rs b/crates/nu-command/src/core_commands/mod.rs
index 4d909467d..3472f4d8b 100644
--- a/crates/nu-command/src/core_commands/mod.rs
+++ b/crates/nu-command/src/core_commands/mod.rs
@@ -1,7 +1,9 @@
 mod alias;
 mod def;
 mod do_;
+mod export_def;
 mod help;
+mod hide;
 mod if_;
 mod let_;
 mod module;
@@ -10,7 +12,9 @@ mod use_;
 pub use alias::Alias;
 pub use def::Def;
 pub use do_::Do;
+pub use export_def::ExportDef;
 pub use help::Help;
+pub use hide::Hide;
 pub use if_::If;
 pub use let_::Let;
 pub use module::Module;
diff --git a/crates/nu-command/src/core_commands/use_.rs b/crates/nu-command/src/core_commands/use_.rs
index 30b5e3d0b..3cfae2e49 100644
--- a/crates/nu-command/src/core_commands/use_.rs
+++ b/crates/nu-command/src/core_commands/use_.rs
@@ -14,7 +14,7 @@ impl Command for Use {
     }
 
     fn signature(&self) -> nu_protocol::Signature {
-        Signature::build("use").required("module_name", SyntaxShape::String, "module name")
+        Signature::build("use").required("pattern", SyntaxShape::String, "import pattern")
     }
 
     fn run(
diff --git a/crates/nu-command/src/default_context.rs b/crates/nu-command/src/default_context.rs
index dc119edc5..6d6b474d0 100644
--- a/crates/nu-command/src/default_context.rs
+++ b/crates/nu-command/src/default_context.rs
@@ -19,12 +19,14 @@ pub fn create_default_context() -> Rc<RefCell<EngineState>> {
         working_set.add_decl(Box::new(Def));
         working_set.add_decl(Box::new(Do));
         working_set.add_decl(Box::new(Each));
+        working_set.add_decl(Box::new(ExportDef));
         working_set.add_decl(Box::new(External));
         working_set.add_decl(Box::new(For));
         working_set.add_decl(Box::new(From));
         working_set.add_decl(Box::new(FromJson));
         working_set.add_decl(Box::new(Get));
         working_set.add_decl(Box::new(Help));
+        working_set.add_decl(Box::new(Hide));
         working_set.add_decl(Box::new(If));
         working_set.add_decl(Box::new(Length));
         working_set.add_decl(Box::new(Let));
diff --git a/crates/nu-parser/src/errors.rs b/crates/nu-parser/src/errors.rs
index 58123aac0..444873d1a 100644
--- a/crates/nu-parser/src/errors.rs
+++ b/crates/nu-parser/src/errors.rs
@@ -57,6 +57,14 @@ pub enum ParseError {
     #[diagnostic(code(nu::parser::expected_keyword), url(docsrs))]
     ExpectedKeyword(String, #[label("expected {0}")] Span),
 
+    #[error("Unexpected keyword.")]
+    #[diagnostic(
+        code(nu::parser::unexpected_keyword),
+        url(docsrs),
+        help("'export' keyword is allowed only in a module.")
+    )]
+    UnexpectedKeyword(String, #[label("unexpected {0}")] Span),
+
     #[error("Multiple rest params.")]
     #[diagnostic(code(nu::parser::multiple_rest_params), url(docsrs))]
     MultipleRestParams(#[label = "multiple rest params"] Span),
@@ -69,6 +77,10 @@ pub enum ParseError {
     #[diagnostic(code(nu::parser::module_not_found), url(docsrs))]
     ModuleNotFound(#[label = "module not found"] Span),
 
+    #[error("Duplicate command definition within a block.")]
+    #[diagnostic(code(nu::parser::duplicate_command_def), url(docsrs))]
+    DuplicateCommandDef(#[label = "defined more than once"] Span),
+
     #[error("Unknown command.")]
     #[diagnostic(
         code(nu::parser::unknown_command),
diff --git a/crates/nu-parser/src/parse_keywords.rs b/crates/nu-parser/src/parse_keywords.rs
index e516da309..033a21e73 100644
--- a/crates/nu-parser/src/parse_keywords.rs
+++ b/crates/nu-parser/src/parse_keywords.rs
@@ -13,9 +13,16 @@ use crate::{
     ParseError,
 };
 
-pub fn parse_def_predecl(working_set: &mut StateWorkingSet, spans: &[Span]) {
+pub fn parse_def_predecl(working_set: &mut StateWorkingSet, spans: &[Span]) -> Option<ParseError> {
     let name = working_set.get_span_contents(spans[0]);
 
+    // handle "export def" same as "def"
+    let (name, spans) = if name == b"export" && spans.len() >= 2 {
+        (working_set.get_span_contents(spans[1]), &spans[1..])
+    } else {
+        (name, spans)
+    };
+
     if name == b"def" && spans.len() >= 4 {
         let (name_expr, ..) = parse_string(working_set, spans[1]);
         let name = name_expr.as_string();
@@ -35,9 +42,13 @@ pub fn parse_def_predecl(working_set: &mut StateWorkingSet, spans: &[Span]) {
             signature.name = name;
             let decl = signature.predeclare();
 
-            working_set.add_decl(decl);
+            if working_set.add_predecl(decl).is_some() {
+                return Some(ParseError::DuplicateCommandDef(spans[1]));
+            }
         }
     }
+
+    None
 }
 
 pub fn parse_def(
@@ -88,17 +99,22 @@ pub fn parse_def(
                     call.positional.push(block);
 
                     if let (Some(name), Some(mut signature), Some(block_id)) =
-                        (name, signature, block_id)
+                        (&name, signature, block_id)
                     {
-                        let decl_id = working_set
-                            .find_decl(name.as_bytes())
-                            .expect("internal error: predeclaration failed to add definition");
+                        if let Some(decl_id) = working_set.find_decl(name.as_bytes()) {
+                            let declaration = working_set.get_decl_mut(decl_id);
 
-                        let declaration = working_set.get_decl_mut(decl_id);
+                            signature.name = name.clone();
 
-                        signature.name = name;
-
-                        *declaration = signature.into_block_command(block_id);
+                            *declaration = signature.into_block_command(block_id);
+                        } else {
+                            error = error.or_else(|| {
+                                Some(ParseError::UnknownState(
+                                    "Could not define hidden command".into(),
+                                    spans[1],
+                                ))
+                            });
+                        };
                     }
                 } else {
                     let err_span = Span {
@@ -111,6 +127,19 @@ pub fn parse_def(
                 }
                 working_set.exit_scope();
 
+                if let Some(name) = name {
+                    // It's OK if it returns None: The decl was already merged in previous parse
+                    // pass.
+                    working_set.merge_predecl(name.as_bytes());
+                } else {
+                    error = error.or_else(|| {
+                        Some(ParseError::UnknownState(
+                            "Could not get string from string expression".into(),
+                            *name_span,
+                        ))
+                    });
+                }
+
                 call
             } else {
                 let err_span = Span {
@@ -218,6 +247,71 @@ pub fn parse_alias(
     )
 }
 
+pub fn parse_export(
+    working_set: &mut StateWorkingSet,
+    spans: &[Span],
+) -> (Statement, Option<ParseError>) {
+    let bytes = working_set.get_span_contents(spans[0]);
+
+    if bytes == b"export" && spans.len() >= 3 {
+        let export_name = working_set.get_span_contents(spans[1]);
+
+        match export_name {
+            b"def" => {
+                let (stmt, err) = parse_def(working_set, &spans[1..]);
+
+                let export_def_decl_id = working_set
+                    .find_decl(b"export def")
+                    .expect("internal error: missing 'export def' command");
+
+                // Trying to warp the 'def' call into the 'export def' in a very clumsy way
+                let stmt = if let Statement::Pipeline(ref pipe) = stmt {
+                    if !pipe.expressions.is_empty() {
+                        if let Expr::Call(ref call) = pipe.expressions[0].expr {
+                            let mut call = call.clone();
+
+                            call.head = span(&spans[0..=1]);
+                            call.decl_id = export_def_decl_id;
+
+                            Statement::Pipeline(Pipeline::from_vec(vec![Expression {
+                                expr: Expr::Call(call),
+                                span: span(spans),
+                                ty: Type::Unknown,
+                                custom_completion: None,
+                            }]))
+                        } else {
+                            stmt
+                        }
+                    } else {
+                        stmt
+                    }
+                } else {
+                    stmt
+                };
+
+                (stmt, err)
+            }
+            _ => (
+                garbage_statement(spans),
+                Some(ParseError::Expected(
+                    // TODO: Fill in more as they come
+                    "def keyword".into(),
+                    spans[1],
+                )),
+            ),
+        }
+    } else {
+        (
+            garbage_statement(spans),
+            Some(ParseError::UnknownState(
+                // TODO: fill in more as they come
+                "Expected structure: export def [] {}".into(),
+                span(spans),
+            )),
+        )
+    }
+}
+
 pub fn parse_module(
     working_set: &mut StateWorkingSet,
     spans: &[Span],
@@ -307,15 +401,21 @@ pub fn parse_module(
                         b"def" => {
                             let (stmt, err) = parse_def(working_set, &pipeline.commands[0].parts);
 
+                            (stmt, err)
+                        }
+                        b"export" => {
+                            let (stmt, err) =
+                                parse_export(working_set, &pipeline.commands[0].parts);
+
                             if err.is_none() {
                                 let decl_name =
-                                    working_set.get_span_contents(pipeline.commands[0].parts[1]);
+                                    // parts[2] is safe since it's checked in parse_def already
+                                    working_set.get_span_contents(pipeline.commands[0].parts[2]);
 
                                 let decl_id = working_set
                                     .find_decl(decl_name)
                                     .expect("internal error: failed to find added declaration");
 
-                                // TODO: Later, we want to put this behind 'export'
                                 exports.push((decl_name.into(), decl_id));
                             }
 
@@ -324,7 +424,8 @@ pub fn parse_module(
                         _ => (
                             garbage_statement(&pipeline.commands[0].parts),
                             Some(ParseError::Expected(
-                                "def".into(),
+                                // TODO: Fill in more as they com
+                                "def or export keyword".into(),
                                 pipeline.commands[0].parts[0],
                             )),
                         ),
@@ -393,8 +494,6 @@ pub fn parse_use(
     let mut error = None;
     let bytes = working_set.get_span_contents(spans[0]);
 
-    // TODO: Currently, this directly imports the module's definitions into the current scope.
-    // Later, we want to put them behind the module's name and add selective importing
     if bytes == b"use" && spans.len() >= 2 {
         let (module_name_expr, err) = parse_string(working_set, spans[1]);
         error = error.or(err);
@@ -403,8 +502,6 @@ pub fn parse_use(
         error = error.or(err);
 
         let exports = if let Some(block_id) = working_set.find_module(&import_pattern.head) {
-            // TODO: Since we don't use the Block at all, we might just as well create a separate
-            // Module that holds only the exports, without having Blocks in the way.
             working_set.get_block(block_id).exports.clone()
         } else {
             return (
@@ -492,6 +589,57 @@ pub fn parse_use(
     }
 }
 
+pub fn parse_hide(
+    working_set: &mut StateWorkingSet,
+    spans: &[Span],
+) -> (Statement, Option<ParseError>) {
+    let mut error = None;
+    let bytes = working_set.get_span_contents(spans[0]);
+
+    if bytes == b"hide" && spans.len() >= 2 {
+        let (name_expr, err) = parse_string(working_set, spans[1]);
+        error = error.or(err);
+
+        let name_bytes: Vec<u8> = working_set.get_span_contents(spans[1]).into();
+
+        // TODO: Do the import pattern stuff for bulk-hiding
+
+        if working_set.hide_decl(&name_bytes).is_none() {
+            error = error.or_else(|| Some(ParseError::UnknownCommand(spans[1])));
+        }
+
+        // Create the Hide command call
+        let hide_decl_id = working_set
+            .find_decl(b"hide")
+            .expect("internal error: missing hide command");
+
+        let call = Box::new(Call {
+            head: spans[0],
+            decl_id: hide_decl_id,
+            positional: vec![name_expr],
+            named: vec![],
+        });
+
+        (
+            Statement::Pipeline(Pipeline::from_vec(vec![Expression {
+                expr: Expr::Call(call),
+                span: span(spans),
+                ty: Type::Unknown,
+                custom_completion: None,
+            }])),
+            error,
+        )
+    } else {
+        (
+            garbage_statement(spans),
+            Some(ParseError::UnknownState(
+                "Expected structure: hide <name>".into(),
+                span(spans),
+            )),
+        )
+    }
+}
+
 pub fn parse_let(
     working_set: &mut StateWorkingSet,
     spans: &[Span],
diff --git a/crates/nu-parser/src/parser.rs b/crates/nu-parser/src/parser.rs
index db973c46c..fa9703a73 100644
--- a/crates/nu-parser/src/parser.rs
+++ b/crates/nu-parser/src/parser.rs
@@ -14,7 +14,7 @@ use nu_protocol::{
 };
 
 use crate::parse_keywords::{
-    parse_alias, parse_def, parse_def_predecl, parse_let, parse_module, parse_use,
+    parse_alias, parse_def, parse_def_predecl, parse_hide, parse_let, parse_module, parse_use,
 };
 
 #[derive(Debug, Clone)]
@@ -2619,6 +2619,11 @@ pub fn parse_statement(
         b"alias" => parse_alias(working_set, spans),
         b"module" => parse_module(working_set, spans),
         b"use" => parse_use(working_set, spans),
+        b"export" => (
+            garbage_statement(spans),
+            Some(ParseError::UnexpectedKeyword("export".into(), spans[0])),
+        ),
+        b"hide" => parse_hide(working_set, spans),
         _ => {
             let (expr, err) = parse_expression(working_set, spans);
             (Statement::Pipeline(Pipeline::from_vec(vec![expr])), err)
@@ -2635,16 +2640,18 @@ pub fn parse_block(
         working_set.enter_scope();
     }
 
+    let mut error = None;
+
     // Pre-declare any definition so that definitions
     // that share the same block can see each other
     for pipeline in &lite_block.block {
         if pipeline.commands.len() == 1 {
-            parse_def_predecl(working_set, &pipeline.commands[0].parts);
+            if let Some(err) = parse_def_predecl(working_set, &pipeline.commands[0].parts) {
+                error = error.or(Some(err));
+            }
         }
     }
 
-    let mut error = None;
-
     let block: Block = lite_block
         .block
         .iter()
diff --git a/crates/nu-protocol/src/engine/engine_state.rs b/crates/nu-protocol/src/engine/engine_state.rs
index f0920ed5c..bbe6bdb1c 100644
--- a/crates/nu-protocol/src/engine/engine_state.rs
+++ b/crates/nu-protocol/src/engine/engine_state.rs
@@ -1,7 +1,10 @@
 use super::Command;
 use crate::{ast::Block, BlockId, DeclId, Signature, Span, Type, VarId};
 use core::panic;
-use std::{collections::HashMap, slice::Iter};
+use std::{
+    collections::{HashMap, HashSet},
+    slice::Iter,
+};
 
 pub struct EngineState {
     files: Vec<(String, usize, usize)>,
@@ -18,6 +21,7 @@ pub struct ScopeFrame {
     decls: HashMap<Vec<u8>, DeclId>,
     aliases: HashMap<Vec<u8>, Vec<Span>>,
     modules: HashMap<Vec<u8>, BlockId>,
+    hiding: HashSet<DeclId>,
 }
 
 impl ScopeFrame {
@@ -27,6 +31,7 @@ impl ScopeFrame {
             decls: HashMap::new(),
             aliases: HashMap::new(),
             modules: HashMap::new(),
+            hiding: HashSet::new(),
         }
     }
 
@@ -81,6 +86,9 @@ impl EngineState {
             for item in first.modules.into_iter() {
                 last.modules.insert(item.0, item.1);
             }
+            for item in first.hiding.into_iter() {
+                last.hiding.insert(item);
+            }
         }
     }
 
@@ -124,9 +132,15 @@ impl EngineState {
     }
 
     pub fn find_decl(&self, name: &[u8]) -> Option<DeclId> {
+        let mut hiding: HashSet<DeclId> = HashSet::new();
+
         for scope in self.scope.iter().rev() {
+            hiding.extend(&scope.hiding);
+
             if let Some(decl_id) = scope.decls.get(name) {
-                return Some(*decl_id);
+                if !hiding.contains(decl_id) {
+                    return Some(*decl_id);
+                }
             }
         }
 
@@ -238,9 +252,10 @@ pub struct StateWorkingSet<'a> {
 pub struct StateDelta {
     files: Vec<(String, usize, usize)>,
     pub(crate) file_contents: Vec<u8>,
-    vars: Vec<Type>,              // indexed by VarId
-    decls: Vec<Box<dyn Command>>, // indexed by DeclId
-    blocks: Vec<Block>,           // indexed by BlockId
+    vars: Vec<Type>,                    // indexed by VarId
+    decls: Vec<Box<dyn Command>>,       // indexed by DeclId
+    blocks: Vec<Block>,                 // indexed by BlockId
+    predecls: HashMap<Vec<u8>, DeclId>, // this should get erased after every def call
     pub scope: Vec<ScopeFrame>,
 }
 
@@ -274,6 +289,7 @@ impl<'a> StateWorkingSet<'a> {
                 file_contents: vec![],
                 vars: vec![],
                 decls: vec![],
+                predecls: HashMap::new(),
                 blocks: vec![],
                 scope: vec![ScopeFrame::new()],
             },
@@ -304,11 +320,71 @@ impl<'a> StateWorkingSet<'a> {
             .scope
             .last_mut()
             .expect("internal error: missing required scope frame");
+
         scope_frame.decls.insert(name, decl_id);
 
         decl_id
     }
 
+    pub fn add_predecl(&mut self, decl: Box<dyn Command>) -> Option<DeclId> {
+        let name = decl.name().as_bytes().to_vec();
+
+        self.delta.decls.push(decl);
+        let decl_id = self.num_decls() - 1;
+
+        self.delta.predecls.insert(name, decl_id)
+    }
+
+    pub fn merge_predecl(&mut self, name: &[u8]) -> Option<DeclId> {
+        if let Some(decl_id) = self.delta.predecls.remove(name) {
+            let scope_frame = self
+                .delta
+                .scope
+                .last_mut()
+                .expect("internal error: missing required scope frame");
+
+            scope_frame.decls.insert(name.into(), decl_id);
+
+            return Some(decl_id);
+        }
+
+        None
+    }
+
+    pub fn hide_decl(&mut self, name: &[u8]) -> Option<DeclId> {
+        let mut hiding: HashSet<DeclId> = HashSet::new();
+
+        // Since we can mutate scope frames in delta, remove the id directly
+        for scope in self.delta.scope.iter_mut().rev() {
+            hiding.extend(&scope.hiding);
+
+            if let Some(decl_id) = scope.decls.remove(name) {
+                return Some(decl_id);
+            }
+        }
+
+        // We cannot mutate the permanent state => store the information in the current scope frame
+        let last_scope_frame = self
+            .delta
+            .scope
+            .last_mut()
+            .expect("internal error: missing required scope frame");
+
+        for scope in self.permanent_state.scope.iter().rev() {
+            hiding.extend(&scope.hiding);
+
+            if let Some(decl_id) = scope.decls.get(name) {
+                if !hiding.contains(decl_id) {
+                    // Do not hide already hidden decl
+                    last_scope_frame.hiding.insert(*decl_id);
+                    return Some(*decl_id);
+                }
+            }
+        }
+
+        None
+    }
+
     pub fn add_block(&mut self, block: Block) -> BlockId {
         self.delta.blocks.push(block);
 
@@ -416,15 +492,27 @@ impl<'a> StateWorkingSet<'a> {
     }
 
     pub fn find_decl(&self, name: &[u8]) -> Option<DeclId> {
+        let mut hiding: HashSet<DeclId> = HashSet::new();
+
+        if let Some(decl_id) = self.delta.predecls.get(name) {
+            return Some(*decl_id);
+        }
+
         for scope in self.delta.scope.iter().rev() {
+            hiding.extend(&scope.hiding);
+
             if let Some(decl_id) = scope.decls.get(name) {
                 return Some(*decl_id);
             }
         }
 
         for scope in self.permanent_state.scope.iter().rev() {
+            hiding.extend(&scope.hiding);
+
             if let Some(decl_id) = scope.decls.get(name) {
-                return Some(*decl_id);
+                if !hiding.contains(decl_id) {
+                    return Some(*decl_id);
+                }
             }
         }
 
diff --git a/src/tests.rs b/src/tests.rs
index 3ac7dc681..7416aecb6 100644
--- a/src/tests.rs
+++ b/src/tests.rs
@@ -346,7 +346,7 @@ fn better_block_types() -> TestResult {
 #[test]
 fn module_imports_1() -> TestResult {
     run_test(
-        r#"module foo { def a [] { 1 }; def b [] { 2 } }; use foo; foo.a"#,
+        r#"module foo { export def a [] { 1 }; def b [] { 2 } }; use foo; foo.a"#,
         "1",
     )
 }
@@ -354,7 +354,7 @@ fn module_imports_1() -> TestResult {
 #[test]
 fn module_imports_2() -> TestResult {
     run_test(
-        r#"module foo { def a [] { 1 }; def b [] { 2 } }; use foo.a; a"#,
+        r#"module foo { export def a [] { 1 }; def b [] { 2 } }; use foo.a; a"#,
         "1",
     )
 }
@@ -362,7 +362,7 @@ fn module_imports_2() -> TestResult {
 #[test]
 fn module_imports_3() -> TestResult {
     run_test(
-        r#"module foo { def a [] { 1 }; def b [] { 2 } }; use foo.*; b"#,
+        r#"module foo { export def a [] { 1 }; export def b [] { 2 } }; use foo.*; b"#,
         "2",
     )
 }
@@ -370,7 +370,7 @@ fn module_imports_3() -> TestResult {
 #[test]
 fn module_imports_4() -> TestResult {
     fail_test(
-        r#"module foo { def a [] { 1 }; def b [] { 2 } }; use foo.c"#,
+        r#"module foo { export def a [] { 1 }; export def b [] { 2 } }; use foo.c"#,
         "not find import",
     )
 }
@@ -378,11 +378,77 @@ fn module_imports_4() -> TestResult {
 #[test]
 fn module_imports_5() -> TestResult {
     run_test(
-        r#"module foo { def a [] { 1 }; def b [] { 2 }; def c [] { 3 } }; use foo.[a, c]; c"#,
+        r#"module foo { export def a [] { 1 }; def b [] { 2 }; export def c [] { 3 } }; use foo.[a, c]; c"#,
         "3",
     )
 }
 
+#[test]
+fn module_import_uses_internal_command() -> TestResult {
+    run_test(
+        r#"module foo { def b [] { 2 }; export def a [] { b }  }; use foo; foo.a"#,
+        "2",
+    )
+}
+
+#[test]
+fn hides_def() -> TestResult {
+    fail_test(r#"def foo [] { "foo" }; hide foo; foo"#, "not found")
+}
+
+#[test]
+fn hides_def_then_redefines() -> TestResult {
+    fail_test(
+        r#"def foo [] { "foo" }; hide foo; def foo [] { "bar" }; foo"#,
+        "defined more than once",
+    )
+}
+
+#[test]
+fn hides_def_in_scope_1() -> TestResult {
+    fail_test(r#"def foo [] { "foo" }; do { hide foo; foo }"#, "not found")
+}
+
+#[test]
+fn hides_def_in_scope_2() -> TestResult {
+    run_test(
+        r#"def foo [] { "foo" }; do { def foo [] { "bar" }; hide foo; foo }"#,
+        "foo",
+    )
+}
+
+#[test]
+fn hides_def_in_scope_3() -> TestResult {
+    fail_test(
+        r#"def foo [] { "foo" }; do { hide foo; def foo [] { "bar" }; hide foo; foo }"#,
+        "not found",
+    )
+}
+
+#[test]
+fn hides_def_in_scope_4() -> TestResult {
+    fail_test(
+        r#"def foo [] { "foo" }; do { def foo [] { "bar" }; hide foo; hide foo; foo }"#,
+        "not found",
+    )
+}
+
+#[test]
+fn hide_twice_not_allowed() -> TestResult {
+    fail_test(
+        r#"def foo [] { "foo" }; hide foo; hide foo"#,
+        "unknown command",
+    )
+}
+
+#[test]
+fn def_twice_should_fail() -> TestResult {
+    fail_test(
+        r#"def foo [] { "foo" }; def foo [] { "bar" }"#,
+        "defined more than once",
+    )
+}
+
 #[test]
 fn from_json_1() -> TestResult {
     run_test(r#"('{"name": "Fred"}' | from json).name"#, "Fred")