diff --git a/asg/src/expression/sizeof.rs b/asg/src/expression/lengthof.rs
similarity index 67%
rename from asg/src/expression/sizeof.rs
rename to asg/src/expression/lengthof.rs
index bc580eeae1..ee8c883ebb 100644
--- a/asg/src/expression/sizeof.rs
+++ b/asg/src/expression/lengthof.rs
@@ -21,19 +21,19 @@ use leo_errors::{Result, Span};
 use std::cell::Cell;
 
 #[derive(Clone)]
-pub struct SizeOfExpression<'a> {
+pub struct LengthOfExpression<'a> {
     pub parent: Cell<Option<&'a Expression<'a>>>,
     pub span: Option<Span>,
     pub inner: Cell<&'a Expression<'a>>,
 }
 
-impl<'a> Node for SizeOfExpression<'a> {
+impl<'a> Node for LengthOfExpression<'a> {
     fn span(&self) -> Option<&Span> {
         self.span.as_ref()
     }
 }
 
-impl<'a> ExpressionNode<'a> for SizeOfExpression<'a> {
+impl<'a> ExpressionNode<'a> for LengthOfExpression<'a> {
     fn set_parent(&self, parent: &'a Expression<'a>) {
         self.parent.replace(Some(parent));
     }
@@ -47,10 +47,7 @@ impl<'a> ExpressionNode<'a> for SizeOfExpression<'a> {
     }
 
     fn get_type(&self) -> Option<Type<'a>> {
-        // TODO: make decision on get type method
-        // Should it be always u32? For indexes?
-        // How type casts are applied to this?
-        Some(Type::Integer(IntegerType::U32))
+        Some(Type::Integer(IntegerType::U32)) // For now we stick to U32 value type
     }
 
     fn is_mut_ref(&self) -> bool {
@@ -58,16 +55,6 @@ impl<'a> ExpressionNode<'a> for SizeOfExpression<'a> {
     }
 
     fn const_value(&self) -> Option<ConstValue> {
-        let _value = self.inner.get().const_value()?;
-        // match value {
-        //     ConstValue::Int(int) => match &self.target_type {
-        //         Type::Integer(target) => Some(ConstValue::Int(int.cast_to(target))),
-        //         _ => None,
-        //     },
-        //     _ => None,
-        // }
-
-        // TODO: IMPLEMENT CONST VALUE
         None
     }
 
@@ -76,15 +63,15 @@ impl<'a> ExpressionNode<'a> for SizeOfExpression<'a> {
     }
 }
 
-impl<'a> FromAst<'a, leo_ast::SizeOfExpression> for SizeOfExpression<'a> {
+impl<'a> FromAst<'a, leo_ast::LengthOfExpression> for LengthOfExpression<'a> {
     fn from_ast(
         scope: &'a Scope<'a>,
-        value: &leo_ast::SizeOfExpression,
+        value: &leo_ast::LengthOfExpression,
         _expected_type: Option<PartialType<'a>>,
-    ) -> Result<SizeOfExpression<'a>> {
+    ) -> Result<LengthOfExpression<'a>> {
         let inner = <&Expression<'a>>::from_ast(scope, &*value.inner, None)?;
 
-        Ok(SizeOfExpression {
+        Ok(LengthOfExpression {
             parent: Cell::new(None),
             span: Some(value.span.clone()),
             inner: Cell::new(inner),
@@ -92,9 +79,9 @@ impl<'a> FromAst<'a, leo_ast::SizeOfExpression> for SizeOfExpression<'a> {
     }
 }
 
-impl<'a> Into<leo_ast::SizeOfExpression> for &SizeOfExpression<'a> {
-    fn into(self) -> leo_ast::SizeOfExpression {
-        leo_ast::SizeOfExpression {
+impl<'a> Into<leo_ast::LengthOfExpression> for &LengthOfExpression<'a> {
+    fn into(self) -> leo_ast::LengthOfExpression {
+        leo_ast::LengthOfExpression {
             inner: Box::new(self.inner.get().into()),
             span: self.span.clone().unwrap_or_default(),
         }
diff --git a/asg/src/expression/mod.rs b/asg/src/expression/mod.rs
index 34c0c959bd..734b227344 100644
--- a/asg/src/expression/mod.rs
+++ b/asg/src/expression/mod.rs
@@ -65,8 +65,8 @@ pub use variable_ref::*;
 mod cast;
 pub use cast::*;
 
-mod sizeof;
-pub use sizeof::*;
+mod lengthof;
+pub use lengthof::*;
 
 use crate::{ConstValue, FromAst, Node, PartialType, Scope, Type};
 use leo_errors::{Result, Span};
@@ -79,7 +79,7 @@ pub enum Expression<'a> {
     Unary(UnaryExpression<'a>),
     Ternary(TernaryExpression<'a>),
     Cast(CastExpression<'a>),
-    SizeOf(SizeOfExpression<'a>),
+    LengthOf(LengthOfExpression<'a>),
 
     ArrayInline(ArrayInlineExpression<'a>),
     ArrayInit(ArrayInitExpression<'a>),
@@ -111,7 +111,7 @@ impl<'a> Node for Expression<'a> {
             Unary(x) => x.span(),
             Ternary(x) => x.span(),
             Cast(x) => x.span(),
-            SizeOf(x) => x.span(),
+            LengthOf(x) => x.span(),
             ArrayInline(x) => x.span(),
             ArrayInit(x) => x.span(),
             ArrayAccess(x) => x.span(),
@@ -146,7 +146,7 @@ impl<'a> ExpressionNode<'a> for Expression<'a> {
             Unary(x) => x.set_parent(parent),
             Ternary(x) => x.set_parent(parent),
             Cast(x) => x.set_parent(parent),
-            SizeOf(x) => x.set_parent(parent),
+            LengthOf(x) => x.set_parent(parent),
             ArrayInline(x) => x.set_parent(parent),
             ArrayInit(x) => x.set_parent(parent),
             ArrayAccess(x) => x.set_parent(parent),
@@ -168,7 +168,7 @@ impl<'a> ExpressionNode<'a> for Expression<'a> {
             Unary(x) => x.get_parent(),
             Ternary(x) => x.get_parent(),
             Cast(x) => x.get_parent(),
-            SizeOf(x) => x.get_parent(),
+            LengthOf(x) => x.get_parent(),
             ArrayInline(x) => x.get_parent(),
             ArrayInit(x) => x.get_parent(),
             ArrayAccess(x) => x.get_parent(),
@@ -190,7 +190,7 @@ impl<'a> ExpressionNode<'a> for Expression<'a> {
             Unary(x) => x.enforce_parents(expr),
             Ternary(x) => x.enforce_parents(expr),
             Cast(x) => x.enforce_parents(expr),
-            SizeOf(x) => x.enforce_parents(expr),
+            LengthOf(x) => x.enforce_parents(expr),
             ArrayInline(x) => x.enforce_parents(expr),
             ArrayInit(x) => x.enforce_parents(expr),
             ArrayAccess(x) => x.enforce_parents(expr),
@@ -212,7 +212,7 @@ impl<'a> ExpressionNode<'a> for Expression<'a> {
             Unary(x) => x.get_type(),
             Ternary(x) => x.get_type(),
             Cast(x) => x.get_type(),
-            SizeOf(x) => x.get_type(),
+            LengthOf(x) => x.get_type(),
             ArrayInline(x) => x.get_type(),
             ArrayInit(x) => x.get_type(),
             ArrayAccess(x) => x.get_type(),
@@ -234,7 +234,7 @@ impl<'a> ExpressionNode<'a> for Expression<'a> {
             Unary(x) => x.is_mut_ref(),
             Ternary(x) => x.is_mut_ref(),
             Cast(x) => x.is_mut_ref(),
-            SizeOf(x) => x.is_mut_ref(),
+            LengthOf(x) => x.is_mut_ref(),
             ArrayInline(x) => x.is_mut_ref(),
             ArrayInit(x) => x.is_mut_ref(),
             ArrayAccess(x) => x.is_mut_ref(),
@@ -256,7 +256,7 @@ impl<'a> ExpressionNode<'a> for Expression<'a> {
             Unary(x) => x.const_value(),
             Ternary(x) => x.const_value(),
             Cast(x) => x.const_value(),
-            SizeOf(x) => x.const_value(),
+            LengthOf(x) => x.const_value(),
             ArrayInline(x) => x.const_value(),
             ArrayInit(x) => x.const_value(),
             ArrayAccess(x) => x.const_value(),
@@ -278,7 +278,7 @@ impl<'a> ExpressionNode<'a> for Expression<'a> {
             Unary(x) => x.is_consty(),
             Ternary(x) => x.is_consty(),
             Cast(x) => x.is_consty(),
-            SizeOf(x) => x.is_consty(),
+            LengthOf(x) => x.is_consty(),
             ArrayInline(x) => x.is_consty(),
             ArrayInit(x) => x.is_consty(),
             ArrayAccess(x) => x.is_consty(),
@@ -317,9 +317,9 @@ impl<'a> FromAst<'a, leo_ast::Expression> for &'a Expression<'a> {
                 .context
                 .alloc_expression(CastExpression::from_ast(scope, cast, expected_type).map(Expression::Cast)?),
 
-            SizeOf(sizeof) => scope
-                .context
-                .alloc_expression(SizeOfExpression::from_ast(scope, sizeof, expected_type).map(Expression::SizeOf)?),
+            LengthOf(lengthof) => scope.context.alloc_expression(
+                LengthOfExpression::from_ast(scope, lengthof, expected_type).map(Expression::LengthOf)?,
+            ),
 
             ArrayInline(array_inline) => scope.context.alloc_expression(
                 ArrayInlineExpression::from_ast(scope, array_inline, expected_type).map(Expression::ArrayInline)?,
@@ -373,7 +373,7 @@ impl<'a> Into<leo_ast::Expression> for &Expression<'a> {
             Unary(x) => leo_ast::Expression::Unary(x.into()),
             Ternary(x) => leo_ast::Expression::Ternary(x.into()),
             Cast(x) => leo_ast::Expression::Cast(x.into()),
-            SizeOf(x) => leo_ast::Expression::SizeOf(x.into()),
+            LengthOf(x) => leo_ast::Expression::LengthOf(x.into()),
             ArrayInline(x) => leo_ast::Expression::ArrayInline(x.into()),
             ArrayInit(x) => leo_ast::Expression::ArrayInit(x.into()),
             ArrayAccess(x) => leo_ast::Expression::ArrayAccess(x.into()),
diff --git a/asg/src/reducer/monoidal_director.rs b/asg/src/reducer/monoidal_director.rs
index 182f2aca05..8ce0e1e58b 100644
--- a/asg/src/reducer/monoidal_director.rs
+++ b/asg/src/reducer/monoidal_director.rs
@@ -48,7 +48,7 @@ impl<'a, T: Monoid, R: MonoidalReducerExpression<'a, T>> MonoidalDirector<'a, T,
             Expression::CircuitInit(e) => self.reduce_circuit_init(e),
             Expression::Ternary(e) => self.reduce_ternary_expression(e),
             Expression::Cast(e) => self.reduce_cast_expression(e),
-            Expression::SizeOf(e) => self.reduce_sizeof_expression(e),
+            Expression::LengthOf(e) => self.reduce_lengthof_expression(e),
             Expression::Constant(e) => self.reduce_constant(e),
             Expression::TupleAccess(e) => self.reduce_tuple_access(e),
             Expression::TupleInit(e) => self.reduce_tuple_init(e),
@@ -139,10 +139,10 @@ impl<'a, T: Monoid, R: MonoidalReducerExpression<'a, T>> MonoidalDirector<'a, T,
         self.reducer.reduce_cast_expression(input, inner)
     }
 
-    pub fn reduce_sizeof_expression(&mut self, input: &SizeOfExpression<'a>) -> T {
+    pub fn reduce_lengthof_expression(&mut self, input: &LengthOfExpression<'a>) -> T {
         let inner = self.reduce_expression(input.inner.get());
 
-        self.reducer.reduce_sizeof_expression(input, inner)
+        self.reducer.reduce_lengthof_expression(input, inner)
     }
 
     pub fn reduce_constant(&mut self, input: &Constant<'a>) -> T {
diff --git a/asg/src/reducer/monoidal_reducer.rs b/asg/src/reducer/monoidal_reducer.rs
index d6b5cac1fc..f33b311f26 100644
--- a/asg/src/reducer/monoidal_reducer.rs
+++ b/asg/src/reducer/monoidal_reducer.rs
@@ -68,7 +68,7 @@ pub trait MonoidalReducerExpression<'a, T: Monoid> {
         inner
     }
 
-    fn reduce_sizeof_expression(&mut self, input: &SizeOfExpression<'a>, inner: T) -> T {
+    fn reduce_lengthof_expression(&mut self, input: &LengthOfExpression<'a>, inner: T) -> T {
         inner
     }
 
diff --git a/asg/src/reducer/reconstructing_director.rs b/asg/src/reducer/reconstructing_director.rs
index 708c35a0fe..92029b0c43 100644
--- a/asg/src/reducer/reconstructing_director.rs
+++ b/asg/src/reducer/reconstructing_director.rs
@@ -48,7 +48,7 @@ impl<'a, R: ReconstructingReducerExpression<'a>> ReconstructingDirector<'a, R> {
             Expression::CircuitInit(e) => self.reduce_circuit_init(e),
             Expression::Ternary(e) => self.reduce_ternary_expression(e),
             Expression::Cast(e) => self.reduce_cast_expression(e),
-            Expression::SizeOf(e) => Expression::SizeOf(e), //self.reduce_sizeof_expression(e), // TODO: implement REDUCER
+            Expression::LengthOf(e) => Expression::LengthOf(e), // TODO: implement REDUCER
             Expression::Constant(e) => self.reduce_constant(e),
             Expression::TupleAccess(e) => self.reduce_tuple_access(e),
             Expression::TupleInit(e) => self.reduce_tuple_init(e),
diff --git a/asg/src/reducer/visitor.rs b/asg/src/reducer/visitor.rs
index d577e958bb..4f3b468ab5 100644
--- a/asg/src/reducer/visitor.rs
+++ b/asg/src/reducer/visitor.rs
@@ -76,7 +76,7 @@ pub trait ExpressionVisitor<'a> {
         Default::default()
     }
 
-    fn visit_sizeof_expression(&mut self, input: &SizeOfExpression<'a>) -> VisitResult {
+    fn visit_lengthof_expression(&mut self, input: &LengthOfExpression<'a>) -> VisitResult {
         Default::default()
     }
 
diff --git a/asg/src/reducer/visitor_director.rs b/asg/src/reducer/visitor_director.rs
index 5c56607b3e..5490f4b014 100644
--- a/asg/src/reducer/visitor_director.rs
+++ b/asg/src/reducer/visitor_director.rs
@@ -61,7 +61,7 @@ impl<'a, R: ExpressionVisitor<'a>> VisitorDirector<'a, R> {
                 Expression::CircuitInit(e) => self.visit_circuit_init(e),
                 Expression::Ternary(e) => self.visit_ternary_expression(e),
                 Expression::Cast(e) => self.visit_cast_expression(e),
-                Expression::SizeOf(e) => self.visit_sizeof_expression(e),
+                Expression::LengthOf(e) => self.visit_lengthof_expression(e),
                 Expression::Constant(e) => self.visit_constant(e),
                 Expression::TupleAccess(e) => self.visit_tuple_access(e),
                 Expression::TupleInit(e) => self.visit_tuple_init(e),
@@ -196,8 +196,8 @@ impl<'a, R: ExpressionVisitor<'a>> VisitorDirector<'a, R> {
         }
     }
 
-    pub fn visit_sizeof_expression(&mut self, input: &SizeOfExpression<'a>) -> ConcreteVisitResult {
-        match self.visitor.visit_sizeof_expression(input) {
+    pub fn visit_lengthof_expression(&mut self, input: &LengthOfExpression<'a>) -> ConcreteVisitResult {
+        match self.visitor.visit_lengthof_expression(input) {
             VisitResult::VisitChildren => {
                 self.visit_expression(&input.inner)?;
                 Ok(())
diff --git a/ast/src/expression/sizeof.rs b/ast/src/expression/lengthof.rs
similarity index 91%
rename from ast/src/expression/sizeof.rs
rename to ast/src/expression/lengthof.rs
index 8b41f11f2d..e5dec13a62 100644
--- a/ast/src/expression/sizeof.rs
+++ b/ast/src/expression/lengthof.rs
@@ -19,18 +19,18 @@
 use super::*;
 
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
-pub struct SizeOfExpression {
+pub struct LengthOfExpression {
     pub inner: Box<Expression>,
     pub span: Span,
 }
 
-impl fmt::Display for SizeOfExpression {
+impl fmt::Display for LengthOfExpression {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         write!(f, "sizeof {}", self.inner)
     }
 }
 
-impl Node for SizeOfExpression {
+impl Node for LengthOfExpression {
     fn span(&self) -> &Span {
         &self.span
     }
diff --git a/ast/src/expression/mod.rs b/ast/src/expression/mod.rs
index 7196ee4915..d40dcf109e 100644
--- a/ast/src/expression/mod.rs
+++ b/ast/src/expression/mod.rs
@@ -54,8 +54,8 @@ mod call;
 pub use call::*;
 mod cast;
 pub use cast::*;
-mod sizeof;
-pub use sizeof::*;
+mod lengthof;
+pub use lengthof::*;
 
 /// Expression that evaluates to a value
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
@@ -66,7 +66,7 @@ pub enum Expression {
     Unary(UnaryExpression),
     Ternary(TernaryExpression),
     Cast(CastExpression),
-    SizeOf(SizeOfExpression),
+    LengthOf(LengthOfExpression),
 
     ArrayInline(ArrayInlineExpression),
     ArrayInit(ArrayInitExpression),
@@ -103,7 +103,7 @@ impl Node for Expression {
             CircuitStaticFunctionAccess(n) => n.span(),
             Call(n) => n.span(),
             Cast(n) => n.span(),
-            SizeOf(n) => n.span(),
+            LengthOf(n) => n.span(),
         }
     }
 
@@ -126,7 +126,7 @@ impl Node for Expression {
             CircuitStaticFunctionAccess(n) => n.set_span(span),
             Call(n) => n.set_span(span),
             Cast(n) => n.set_span(span),
-            SizeOf(n) => n.set_span(span),
+            LengthOf(n) => n.set_span(span),
         }
     }
 }
@@ -151,7 +151,7 @@ impl fmt::Display for Expression {
             CircuitStaticFunctionAccess(n) => n.fmt(f),
             Call(n) => n.fmt(f),
             Cast(n) => n.fmt(f),
-            SizeOf(n) => n.fmt(f),
+            LengthOf(n) => n.fmt(f),
         }
     }
 }
diff --git a/ast/src/reducer/reconstructing_director.rs b/ast/src/reducer/reconstructing_director.rs
index 384a3192ff..c74aad5dbc 100644
--- a/ast/src/reducer/reconstructing_director.rs
+++ b/ast/src/reducer/reconstructing_director.rs
@@ -57,7 +57,7 @@ impl<R: ReconstructingReducer> ReconstructingDirector<R> {
             Expression::Unary(unary) => Expression::Unary(self.reduce_unary(unary)?),
             Expression::Ternary(ternary) => Expression::Ternary(self.reduce_ternary(ternary)?),
             Expression::Cast(cast) => Expression::Cast(self.reduce_cast(cast)?),
-            Expression::SizeOf(sizeof) => Expression::SizeOf(sizeof.clone()), // Expression::SizeOf(self.reduce_sizeof(sizeof)?), // TODO: add reducer
+            Expression::LengthOf(sizeof) => Expression::LengthOf(sizeof.clone()), // Expression::LengthOf(self.reduce_sizeof(sizeof)?), // TODO: add reducer
 
             Expression::ArrayInline(array_inline) => Expression::ArrayInline(self.reduce_array_inline(array_inline)?),
             Expression::ArrayInit(array_init) => Expression::ArrayInit(self.reduce_array_init(array_init)?),
diff --git a/compiler/src/expression/expression.rs b/compiler/src/expression/expression.rs
index 0f85165252..4f9eb24711 100644
--- a/compiler/src/expression/expression.rs
+++ b/compiler/src/expression/expression.rs
@@ -98,8 +98,8 @@ impl<'a, F: PrimeField, G: GroupType<F>> ConstrainedProgram<'a, F, G> {
             // Cast
             Expression::Cast(_) => unimplemented!("casts not implemented"),
 
-            // SizeOf
-            Expression::SizeOf(sizeof) => self.enforce_sizeof(cs, sizeof, span),
+            // LengthOf
+            Expression::LengthOf(sizeof) => self.enforce_sizeof(cs, sizeof, span),
 
             // Variables
             Expression::VariableRef(variable_ref) => self.evaluate_ref(variable_ref),
diff --git a/compiler/src/expression/operator/sizeof.rs b/compiler/src/expression/operator/lengthof.rs
similarity index 83%
rename from compiler/src/expression/operator/sizeof.rs
rename to compiler/src/expression/operator/lengthof.rs
index 2f26634b96..440d1020d0 100644
--- a/compiler/src/expression/operator/sizeof.rs
+++ b/compiler/src/expression/operator/lengthof.rs
@@ -21,7 +21,7 @@ use crate::{
     value::{ConstrainedValue, Integer},
     GroupType,
 };
-use leo_asg::{ConstInt, SizeOfExpression};
+use leo_asg::{ConstInt, LengthOfExpression};
 use leo_errors::{Result, Span};
 
 use snarkvm_fields::PrimeField;
@@ -32,16 +32,16 @@ impl<'a, F: PrimeField, G: GroupType<F>> ConstrainedProgram<'a, F, G> {
     pub fn enforce_sizeof<CS: ConstraintSystem<F>>(
         &mut self,
         cs: &mut CS,
-        sizeof: &'a SizeOfExpression<'a>,
-        _span: &Span,
+        lengthof: &'a LengthOfExpression<'a>,
+        span: &Span,
     ) -> Result<ConstrainedValue<'a, F, G>> {
-        let value = self.enforce_expression(cs, sizeof.inner.get())?;
+        let value = self.enforce_expression(cs, lengthof.inner.get())?;
 
         Ok(match value {
             ConstrainedValue::Array(array) => {
                 ConstrainedValue::Integer(Integer::new(&ConstInt::U32(array.len() as u32)))
             }
-            _ => unimplemented!("sizeof can only be used for arrays"),
+            _ => return Err(leo_errors::CompilerError::lengthof_can_only_be_used_on_arrays(span).into()),
         })
     }
 }
diff --git a/compiler/src/expression/operator/mod.rs b/compiler/src/expression/operator/mod.rs
index 773e668d58..2d0e37ccc3 100644
--- a/compiler/src/expression/operator/mod.rs
+++ b/compiler/src/expression/operator/mod.rs
@@ -14,5 +14,5 @@
 // You should have received a copy of the GNU General Public License
 // along with the Leo library. If not, see <https://www.gnu.org/licenses/>.
 
-pub mod sizeof;
-pub use self::sizeof::*;
+pub mod lengthof;
+pub use self::lengthof::*;
diff --git a/errors/src/compiler/compiler_errors.rs b/errors/src/compiler/compiler_errors.rs
index f46b4e9566..84272a3b45 100644
--- a/errors/src/compiler/compiler_errors.rs
+++ b/errors/src/compiler/compiler_errors.rs
@@ -834,4 +834,11 @@ create_errors!(
         msg: format!("no implementation found for `{}`", operation),
         help: None,
     }
+
+    @formatted
+    lengthof_can_only_be_used_on_arrays {
+        args: (),
+        msg: "length() can only be called on an array value".to_string(),
+        help: None,
+    }
 );
diff --git a/grammar/src/main.rs b/grammar/src/main.rs
index 28b9f6da74..d180ef3bb4 100644
--- a/grammar/src/main.rs
+++ b/grammar/src/main.rs
@@ -222,3 +222,8 @@ fn main() -> Result<()> {
 
     Ok(())
 }
+
+#[test]
+fn test_true() {
+    assert!(true);
+}
diff --git a/parser/src/parser/expression.rs b/parser/src/parser/expression.rs
index 233e253f3b..eb07d5f4f0 100644
--- a/parser/src/parser/expression.rs
+++ b/parser/src/parser/expression.rs
@@ -402,8 +402,20 @@ impl ParserContext {
     ///
     pub fn parse_postfix_expression(&mut self) -> Result<Expression> {
         let mut expr = self.parse_primary_expression()?;
-        while let Some(token) = self.eat_any(&[Token::LeftSquare, Token::Dot, Token::LeftParen, Token::DoubleColon]) {
+        while let Some(token) = self.eat_any(&[
+            Token::LeftSquare,
+            Token::Dot,
+            Token::LeftParen,
+            Token::DoubleColon,
+            Token::LengthOf,
+        ]) {
             match token.token {
+                Token::LengthOf => {
+                    expr = Expression::LengthOf(LengthOfExpression {
+                        span: expr.span().clone(),
+                        inner: Box::new(expr),
+                    })
+                }
                 Token::LeftSquare => {
                     if self.eat(Token::DotDot).is_some() {
                         let right = if self.peek_token().as_ref() != &Token::RightSquare {
@@ -727,10 +739,10 @@ impl ParserContext {
                 };
                 Expression::Identifier(ident)
             }
-            Token::SizeOf => Expression::SizeOf(SizeOfExpression {
-                span,
-                inner: Box::new(self.parse_primary_expression()?),
-            }),
+            // Token::LengthOf => Expression::LengthOf(LengthOfExpression {
+            //     span,
+            //     inner: Box::new(self.parse_primary_expression()?),
+            // }),
             token => {
                 return Err(ParserError::unexpected_str(token, "expression", &span).into());
             }
diff --git a/parser/src/tokenizer/lexer.rs b/parser/src/tokenizer/lexer.rs
index 455b125028..7a7c32ed92 100644
--- a/parser/src/tokenizer/lexer.rs
+++ b/parser/src/tokenizer/lexer.rs
@@ -388,6 +388,9 @@ impl Token {
                     return (len, Some(Token::DotDotDot));
                 } else if let Some(len) = eat(input, "..") {
                     return (len, Some(Token::DotDot));
+                } else if let Some(len) = eat(input, ".length()") {
+                    // FIXME: remove this code once we allow method calls
+                    return (len, Some(Token::LengthOf));
                 }
                 return (1, Some(Token::Dot));
             }
@@ -519,7 +522,6 @@ impl Token {
                     "string" => Token::String,
                     "true" => Token::True,
                     "type" => Token::Type,
-                    "sizeof" => Token::SizeOf,
                     "u8" => Token::U8,
                     "u16" => Token::U16,
                     "u32" => Token::U32,
diff --git a/parser/src/tokenizer/token.rs b/parser/src/tokenizer/token.rs
index 6c5f0ff981..97ac2164fd 100644
--- a/parser/src/tokenizer/token.rs
+++ b/parser/src/tokenizer/token.rs
@@ -140,8 +140,9 @@ pub enum Token {
     String,
     Type,
 
-    // Operators
-    SizeOf,
+    // Not yet in ABNF
+    // arr.length() token - hacky zone
+    LengthOf,
 
     // Not yet in ABNF
     // BitAnd,
@@ -199,7 +200,7 @@ pub const KEYWORD_TOKENS: &[Token] = &[
     Token::String,
     Token::True,
     Token::Type,
-    Token::SizeOf,
+    Token::LengthOf,
     Token::U8,
     Token::U16,
     Token::U32,
@@ -312,7 +313,7 @@ impl fmt::Display for Token {
             Static => write!(f, "static"),
             String => write!(f, "string"),
             Type => write!(f, "type"),
-            SizeOf => write!(f, "sizeof"),
+            LengthOf => write!(f, ".length()"), // FIXME
             Eof => write!(f, ""),
             // BitAnd => write!(f, "&"),
             // BitAndEq => write!(f, "&="),
diff --git a/tests/compiler/array_without_size/input/dummy.in b/tests/compiler/array_without_size/input/dummy.in
index 6e43b49ecc..9a0231bcd8 100644
--- a/tests/compiler/array_without_size/input/dummy.in
+++ b/tests/compiler/array_without_size/input/dummy.in
@@ -1,6 +1,7 @@
 [main]
 y: bool = true;
 n: bool = false;
+a: [char; 11] = "hello world";
 
 [registers]
 r0: bool = false;
diff --git a/tests/compiler/array_without_size/length.leo b/tests/compiler/array_without_size/length.leo
new file mode 100644
index 0000000000..234815c8fc
--- /dev/null
+++ b/tests/compiler/array_without_size/length.leo
@@ -0,0 +1,9 @@
+/*
+namespace: Compile
+expectation: Pass
+input_file: input/dummy.in
+*/
+
+function main(a: [char; 11], y: bool) -> bool {
+    return y == (a.length() == 11);
+}
diff --git a/tests/compiler/array_without_size/length_fail.leo b/tests/compiler/array_without_size/length_fail.leo
new file mode 100644
index 0000000000..b9175ecdc5
--- /dev/null
+++ b/tests/compiler/array_without_size/length_fail.leo
@@ -0,0 +1,9 @@
+/*
+namespace: Compile
+expectation: Fail
+input_file: input/dummy.in
+*/
+
+function main(y: bool) {
+    return 10.length() == 10u8;
+}
diff --git a/tests/compiler/array_without_size/length_function.leo b/tests/compiler/array_without_size/length_function.leo
new file mode 100644
index 0000000000..7a1d371943
--- /dev/null
+++ b/tests/compiler/array_without_size/length_function.leo
@@ -0,0 +1,17 @@
+/*
+namespace: Compile
+expectation: Pass
+input_file: input/dummy.in
+*/
+
+function main(y: bool) -> bool {
+    let x = 0u8;
+    for i in 0..strlen("I swear to god I had something for this") {
+        x += 1;
+    }
+    return (x == 39) == y;
+}
+
+function strlen(str: [char; _]) -> u32 {
+    return str.length();
+}
diff --git a/tests/expectations/compiler/compiler/array_without_size/length.leo.out b/tests/expectations/compiler/compiler/array_without_size/length.leo.out
new file mode 100644
index 0000000000..5f40d5fcdd
--- /dev/null
+++ b/tests/expectations/compiler/compiler/array_without_size/length.leo.out
@@ -0,0 +1,22 @@
+---
+namespace: Compile
+expectation: Pass
+outputs:
+  - circuit:
+      num_public_variables: 0
+      num_private_variables: 12
+      num_constraints: 1
+      at: 336f487fe39f24aef980deaaf7d6dddcc0dbfa8f121c3470b05546c1ac13f87e
+      bt: ae35381db5558456a49acb22132b4930efd53b90eb2668df06c5d9c1a6b0ab9f
+      ct: cf1cbb66a638b4860a516671fb74850e6ccf787fe6c4c8d29e9c04efe880bd05
+    output:
+      - input_file: input/dummy.in
+        output:
+          registers:
+            r0:
+              type: bool
+              value: "true"
+    initial_ast: f8b64e1675dcb9624011ccf7a6ee9cd4fd7767f9fffbea3c87cbb21cbe734d67
+    imports_resolved_ast: f8b64e1675dcb9624011ccf7a6ee9cd4fd7767f9fffbea3c87cbb21cbe734d67
+    canonicalized_ast: f8b64e1675dcb9624011ccf7a6ee9cd4fd7767f9fffbea3c87cbb21cbe734d67
+    type_inferenced_ast: 4934eaa23f00ce1dfd8e1062e7a6b3bdbc6c5cd4e5f53641a930e910fde34206
diff --git a/tests/expectations/compiler/compiler/array_without_size/length_fail.leo.out b/tests/expectations/compiler/compiler/array_without_size/length_fail.leo.out
new file mode 100644
index 0000000000..40fa5ba7a6
--- /dev/null
+++ b/tests/expectations/compiler/compiler/array_without_size/length_fail.leo.out
@@ -0,0 +1,5 @@
+---
+namespace: Compile
+expectation: Fail
+outputs:
+  - "Error [EASG0373025]: unexpected type, expected: '()', received: 'bool'\n    --> compiler-test:4:12\n     |\n   4 |     return 10.length() == 10u8;\n     |            ^^^^^^^^^^^^^^^^^^^"
diff --git a/tests/expectations/compiler/compiler/array_without_size/length_function.leo.out b/tests/expectations/compiler/compiler/array_without_size/length_function.leo.out
new file mode 100644
index 0000000000..894eff2349
--- /dev/null
+++ b/tests/expectations/compiler/compiler/array_without_size/length_function.leo.out
@@ -0,0 +1,22 @@
+---
+namespace: Compile
+expectation: Pass
+outputs:
+  - circuit:
+      num_public_variables: 0
+      num_private_variables: 1
+      num_constraints: 1
+      at: 042610d0fd1fe6d6ac112138f8755752f44c7d2a00f1b5960574d6da5cda393f
+      bt: e97756698880ab7555a959a5fb5c6b4e15bd64612aa677adbfe2d0bd91f0a83c
+      ct: cf1cbb66a638b4860a516671fb74850e6ccf787fe6c4c8d29e9c04efe880bd05
+    output:
+      - input_file: input/dummy.in
+        output:
+          registers:
+            r0:
+              type: bool
+              value: "true"
+    initial_ast: 3cd71a0e1c6b7aea15b7822c7ad19f400886e82ded67c55d24046d179d202ab0
+    imports_resolved_ast: 3cd71a0e1c6b7aea15b7822c7ad19f400886e82ded67c55d24046d179d202ab0
+    canonicalized_ast: 2f670f34d1dffb2dd07782b566d6da942ea1cbb0ed5c3da1fc7e78e39fa096f7
+    type_inferenced_ast: 4c616d4451798fff86c86c586729b643ad8194248c22956880f168b40a8eddba