Merge pull request #4 from AleoHQ/development

Multiple variable assignment from function return

benchmark/simple.leo

@@ -1,4 +1,10 @@
-function main() -> (u32) {
+function test() -> (u32, u32) {
-    a = 1 + 1
+    return 4, 4
-    return a
 }
+
+function main() -> (u32, u32) {
+    a, b = test()
+
+    return a, b
+}
+

program/src/ast.rs

@@ -268,6 +268,21 @@ impl<'ast> fmt::Display for Variable<'ast> {
     }
 }
 
+#[derive(Debug, FromPest, PartialEq, Clone)]
+#[pest_ast(rule(Rule::optionally_typed_variable))]
+pub struct OptionallyTypedVariable<'ast> {
+    pub ty: Option<Type<'ast>>,
+    pub id: Variable<'ast>,
+    #[pest_ast(outer())]
+    pub span: Span<'ast>,
+}
+
+impl<'ast> fmt::Display for OptionallyTypedVariable<'ast> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{}", self.id)
+    }
+}
+
 // Access
 
 #[derive(Clone, Debug, FromPest, PartialEq)]
@@ -782,25 +797,6 @@ impl<'ast> FromPest<'ast> for Expression<'ast> {
 
 // Statements
 
-#[derive(Clone, Debug, FromPest, PartialEq)]
-#[pest_ast(rule(Rule::statement_assign))]
-pub struct AssignStatement<'ast> {
-    pub assignee: Assignee<'ast>,
-    pub expression: Expression<'ast>,
-    #[pest_ast(outer())]
-    pub span: Span<'ast>,
-}
-
-#[derive(Clone, Debug, FromPest, PartialEq)]
-#[pest_ast(rule(Rule::statement_definition))]
-pub struct DefinitionStatement<'ast> {
-    pub ty: Type<'ast>,
-    pub variable: Variable<'ast>,
-    pub expression: Expression<'ast>,
-    #[pest_ast(outer())]
-    pub span: Span<'ast>,
-}
-
 #[derive(Clone, Debug, FromPest, PartialEq)]
 #[pest_ast(rule(Rule::statement_return))]
 pub struct ReturnStatement<'ast> {
@@ -820,25 +816,43 @@ pub struct ForStatement<'ast> {
     pub span: Span<'ast>,
 }
 
+#[derive(Clone, Debug, FromPest, PartialEq)]
+#[pest_ast(rule(Rule::statement_multiple_assignment))]
+pub struct MultipleAssignmentStatement<'ast> {
+    pub assignees: Vec<OptionallyTypedVariable<'ast>>,
+    pub function_name: Variable<'ast>,
+    pub arguments: Vec<Expression<'ast>>,
+    #[pest_ast(outer())]
+    pub span: Span<'ast>,
+}
+
+#[derive(Clone, Debug, FromPest, PartialEq)]
+#[pest_ast(rule(Rule::statement_definition))]
+pub struct DefinitionStatement<'ast> {
+    pub ty: Type<'ast>,
+    pub variable: Variable<'ast>,
+    pub expression: Expression<'ast>,
+    #[pest_ast(outer())]
+    pub span: Span<'ast>,
+}
+
+#[derive(Clone, Debug, FromPest, PartialEq)]
+#[pest_ast(rule(Rule::statement_assign))]
+pub struct AssignStatement<'ast> {
+    pub assignee: Assignee<'ast>,
+    pub expression: Expression<'ast>,
+    #[pest_ast(outer())]
+    pub span: Span<'ast>,
+}
+
 #[derive(Clone, Debug, FromPest, PartialEq)]
 #[pest_ast(rule(Rule::statement))]
 pub enum Statement<'ast> {
-    Assign(AssignStatement<'ast>),
-    Definition(DefinitionStatement<'ast>),
     Return(ReturnStatement<'ast>),
     Iteration(ForStatement<'ast>),
-}
+    MultipleAssignment(MultipleAssignmentStatement<'ast>),
-
+    Definition(DefinitionStatement<'ast>),
-impl<'ast> fmt::Display for AssignStatement<'ast> {
+    Assign(AssignStatement<'ast>),
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "{} = {}", self.assignee, self.expression)
-    }
-}
-
-impl<'ast> fmt::Display for DefinitionStatement<'ast> {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "{} {} = {}", self.ty, self.variable, self.expression)
-    }
 }
 
 impl<'ast> fmt::Display for ReturnStatement<'ast> {
@@ -863,13 +877,38 @@ impl<'ast> fmt::Display for ForStatement<'ast> {
     }
 }
 
+impl<'ast> fmt::Display for MultipleAssignmentStatement<'ast> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        for (i, id) in self.assignees.iter().enumerate() {
+            write!(f, "{}", id)?;
+            if i < self.assignees.len() - 1 {
+                write!(f, ", ")?;
+            }
+        }
+        write!(f, " = {}", self.function_name)
+    }
+}
+
+impl<'ast> fmt::Display for DefinitionStatement<'ast> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{} {} = {}", self.ty, self.variable, self.expression)
+    }
+}
+
+impl<'ast> fmt::Display for AssignStatement<'ast> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{} = {}", self.assignee, self.expression)
+    }
+}
+
 impl<'ast> fmt::Display for Statement<'ast> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
-            Statement::Assign(ref statement) => write!(f, "{}", statement),
-            Statement::Definition(ref statement) => write!(f, "{}", statement),
             Statement::Return(ref statement) => write!(f, "{}", statement),
             Statement::Iteration(ref statement) => write!(f, "{}", statement),
+            Statement::MultipleAssignment(ref statement) => write!(f, "{}", statement),
+            Statement::Assign(ref statement) => write!(f, "{}", statement),
+            Statement::Definition(ref statement) => write!(f, "{}", statement),
         }
     }
 }

program/src/constraints/constraints.rs

@@ -90,14 +90,21 @@ impl<F: Field + PrimeField, CS: ConstraintSystem<F>> ResolvedProgram<F, CS> {
             .clone()
             .into_iter()
             .for_each(|statement| match statement {
-                Statement::Definition(variable, expression) => {
+                Statement::Return(expressions) => {
-                    self.enforce_definition_statement(
+                    return_values = self.enforce_return_statement(
                         cs,
                         function.get_name(),
-                        variable,
+                        expressions,
-                        expression,
+                        function.returns.to_owned(),
-                    );
+                    )
                 }
+                Statement::MultipleDefinition(assignees, function_call) => self
+                    .enforce_multiple_definition_statement(
+                        cs,
+                        function.get_name(),
+                        assignees,
+                        function_call,
+                    ),
                 Statement::For(index, start, stop, statements) => {
                     self.enforce_for_statement(
                         cs,
@@ -108,13 +115,13 @@ impl<F: Field + PrimeField, CS: ConstraintSystem<F>> ResolvedProgram<F, CS> {
                         statements,
                     );
                 }
-                Statement::Return(expressions) => {
+                Statement::Definition(variable, expression) => {
-                    return_values = self.enforce_return_statement(
+                    self.enforce_definition_statement(
                         cs,
                         function.get_name(),
-                        expressions,
+                        variable,
-                        function.returns.to_owned(),
+                        expression,
-                    )
+                    );
                 }
             });
 

program/src/constraints/expression.rs

@@ -1,7 +1,9 @@
 //! Methods to enforce constraints on expressions in a resolved aleo program.
 
 use crate::constraints::{new_scope_from_variable, ResolvedProgram, ResolvedValue};
-use crate::{Expression, RangeOrExpression, SpreadOrExpression, StructMember, Variable};
+use crate::{
+    Expression, RangeOrExpression, ResolvedStructMember, SpreadOrExpression, StructMember, Variable,
+};
 
 use snarkos_models::curves::{Field, PrimeField};
 use snarkos_models::gadgets::r1cs::ConstraintSystem;
@@ -221,22 +223,24 @@ impl<F: Field + PrimeField, CS: ConstraintSystem<F>> ResolvedProgram<F, CS> {
         if let Some(resolved_value) = self.get_mut_variable(&variable) {
             match resolved_value {
                 ResolvedValue::StructDefinition(struct_definition) => {
-                    struct_definition
+                    let resolved_members = struct_definition
                         .fields
                         .clone()
                         .iter()
                         .zip(members.clone().into_iter())
-                        .for_each(|(field, member)| {
+                        .map(|(field, member)| {
                             if field.variable != member.variable {
                                 unimplemented!("struct field variables do not match")
                             }
-                            // Resolve and possibly enforce struct fields
+                            // Resolve and enforce struct fields
-                            // do we need to store the results here?
+                            let member_value =
-                            let _result =
                                 self.enforce_expression(cs, scope.clone(), member.expression);
-                        });
 
-                    ResolvedValue::StructExpression(variable, members)
+                            ResolvedStructMember(member.variable, member_value)
+                        })
+                        .collect();
+
+                    ResolvedValue::StructExpression(variable, resolved_members)
                 }
                 _ => unimplemented!("Inline struct type is not defined as a struct"),
             }
@@ -254,11 +258,9 @@ impl<F: Field + PrimeField, CS: ConstraintSystem<F>> ResolvedProgram<F, CS> {
     ) -> ResolvedValue<F> {
         match self.enforce_expression(cs, scope.clone(), *struct_variable) {
             ResolvedValue::StructExpression(_name, members) => {
-                let matched_member = members
+                let matched_member = members.into_iter().find(|member| member.0 == struct_member);
-                    .into_iter()
-                    .find(|member| member.variable == struct_member);
                 match matched_member {
-                    Some(member) => self.enforce_expression(cs, scope.clone(), member.expression),
+                    Some(member) => member.1,
                     None => unimplemented!("Cannot access struct member {}", struct_member.name),
                 }
             }
@@ -269,13 +271,17 @@ impl<F: Field + PrimeField, CS: ConstraintSystem<F>> ResolvedProgram<F, CS> {
     fn enforce_function_access_expression(
         &mut self,
         cs: &mut CS,
-        scope: String,
+        function: &Variable<F>,
-        function: Box<Expression<F>>,
         arguments: Vec<Expression<F>>,
     ) -> ResolvedValue<F> {
-        match self.enforce_expression(cs, scope, *function) {
+        match self.get_mut_variable(function) {
-            ResolvedValue::Function(function) => self.enforce_function(cs, function, arguments),
+            Some(value) => match value.clone() {
-            value => unimplemented!("Cannot call unknown function {}", value),
+                ResolvedValue::Function(function) => {
+                    self.enforce_function(cs, function.to_owned(), arguments)
+                }
+                value => unimplemented!("Cannot make function call to {}", value),
+            },
+            None => unimplemented!("Cannot call unknown function {}", function),
         }
     }
 
@@ -393,7 +399,7 @@ impl<F: Field + PrimeField, CS: ConstraintSystem<F>> ResolvedProgram<F, CS> {
 
             // Functions
             Expression::FunctionCall(function, arguments) => {
-                self.enforce_function_access_expression(cs, scope, function, arguments)
+                self.enforce_function_access_expression(cs, &function, arguments)
             } // _ => unimplemented!(),
         }
     }

program/src/constraints/resolved_value.rs

@@ -1,6 +1,6 @@
 //! The in memory stored value for a defined name in a resolved aleo program.
 
-use crate::types::{Function, Struct, StructMember, Type, Variable};
+use crate::types::{Function, Struct, Type, Variable};
 
 use snarkos_models::curves::{Field, PrimeField};
 use snarkos_models::gadgets::{utilities::boolean::Boolean, utilities::uint32::UInt32};
@@ -13,11 +13,14 @@ pub enum ResolvedValue<F: Field + PrimeField> {
     Boolean(Boolean),
     Array(Vec<ResolvedValue<F>>),
     StructDefinition(Struct<F>),
-    StructExpression(Variable<F>, Vec<StructMember<F>>),
+    StructExpression(Variable<F>, Vec<ResolvedStructMember<F>>),
     Function(Function<F>),
     Return(Vec<ResolvedValue<F>>), // add Null for function returns
 }
 
+#[derive(Clone)]
+pub struct ResolvedStructMember<F: Field + PrimeField>(pub Variable<F>, pub ResolvedValue<F>);
+
 impl<F: Field + PrimeField> ResolvedValue<F> {
     pub(crate) fn match_type(&self, ty: &Type<F>) -> bool {
         match (self, ty) {
@@ -60,7 +63,7 @@ impl<F: Field + PrimeField> fmt::Display for ResolvedValue<F> {
             ResolvedValue::StructExpression(ref variable, ref members) => {
                 write!(f, "{} {{", variable)?;
                 for (i, member) in members.iter().enumerate() {
-                    write!(f, "{}: {}", member.variable, member.expression)?;
+                    write!(f, "{}: {}", member.0, member.1)?;
                     if i < members.len() - 1 {
                         write!(f, ", ")?;
                     }

program/src/constraints/statement.rs

@@ -17,28 +17,21 @@ impl<F: Field + PrimeField, CS: ConstraintSystem<F>> ResolvedProgram<F, CS> {
         }
     }
 
-    pub(crate) fn enforce_definition_statement(
+    fn enforce_definition(
         &mut self,
         cs: &mut CS,
         scope: String,
         assignee: Assignee<F>,
-        expression: Expression<F>,
+        return_value: &mut ResolvedValue<F>,
     ) {
-        // Create or modify the lhs variable in the current function scope
         match assignee {
             Assignee::Variable(name) => {
                 // Store the variable in the current scope
                 let definition_name = new_scope_from_variable(scope.clone(), &name);
 
-                // Evaluate the rhs expression in the current function scope
+                self.store(definition_name, return_value.to_owned());
-                let result = self.enforce_expression(cs, scope, expression);
-
-                self.store(definition_name, result);
             }
             Assignee::Array(array, index_expression) => {
-                // Evaluate the rhs expression in the current function scope
-                let result = &mut self.enforce_expression(cs, scope.clone(), expression);
-
                 // Check that array exists
                 let expected_array_name = self.resolve_assignee(scope.clone(), *array);
 
@@ -51,7 +44,7 @@ impl<F: Field + PrimeField, CS: ConstraintSystem<F>> ResolvedProgram<F, CS> {
                         match self.get_mut(&expected_array_name) {
                             Some(value) => match value {
                                 ResolvedValue::Array(old) => {
-                                    old[index] = result.to_owned();
+                                    old[index] = return_value.to_owned();
                                 }
                                 _ => {
                                     unimplemented!("Cannot assign single index to array of values ")
@@ -75,7 +68,7 @@ impl<F: Field + PrimeField, CS: ConstraintSystem<F>> ResolvedProgram<F, CS> {
 
                         // Modify the range of values of the array in place
                         match self.get_mut(&expected_array_name) {
-                            Some(value) => match (value, result) {
+                            Some(value) => match (value, return_value) {
                                 (ResolvedValue::Array(old), ResolvedValue::Array(new)) => {
                                     let to_index = to_index_option.unwrap_or(old.len());
                                     old.splice(from_index..to_index, new.iter().cloned());
@@ -100,11 +93,10 @@ impl<F: Field + PrimeField, CS: ConstraintSystem<F>> ResolvedProgram<F, CS> {
                     Some(value) => match value {
                         ResolvedValue::StructExpression(_variable, members) => {
                             // Modify the struct member in place
-                            let matched_member = members
+                            let matched_member =
-                                .into_iter()
+                                members.into_iter().find(|member| member.0 == struct_member);
-                                .find(|member| member.variable == struct_member);
                             match matched_member {
-                                Some(mut member) => member.expression = expression,
+                                Some(mut member) => member.1 = return_value.to_owned(),
                                 None => unimplemented!(
                                     "struct member {} does not exist in {}",
                                     struct_member,
@@ -122,7 +114,43 @@ impl<F: Field + PrimeField, CS: ConstraintSystem<F>> ResolvedProgram<F, CS> {
                     }
                 }
             }
+        }
+    }
+
+    pub(crate) fn enforce_definition_statement(
+        &mut self,
+        cs: &mut CS,
+        scope: String,
+        assignee: Assignee<F>,
+        expression: Expression<F>,
+    ) {
+        let result_value = &mut self.enforce_expression(cs, scope.clone(), expression);
+
+        self.enforce_definition(cs, scope, assignee, result_value);
+    }
+
+    pub(crate) fn enforce_multiple_definition_statement(
+        &mut self,
+        cs: &mut CS,
+        scope: String,
+        assignees: Vec<Assignee<F>>,
+        function: Expression<F>,
+    ) {
+        // Expect return values from function
+        let return_values = match self.enforce_expression(cs, scope.clone(), function) {
+            ResolvedValue::Return(values) => values,
+            value => unimplemented!(
+                "multiple assignment only implemented for functions, got {}",
+                value
+            ),
         };
+
+        assignees
+            .into_iter()
+            .zip(return_values.into_iter())
+            .for_each(|(assignee, mut return_value)| {
+                self.enforce_definition(cs, scope.clone(), assignee, &mut return_value);
+            });
     }
 
     pub(crate) fn enforce_return_statement(
@@ -156,15 +184,18 @@ impl<F: Field + PrimeField, CS: ConstraintSystem<F>> ResolvedProgram<F, CS> {
         return_types: Vec<Type<F>>,
     ) {
         match statement {
-            Statement::Definition(variable, expression) => {
+            Statement::Return(statements) => {
-                self.enforce_definition_statement(cs, scope, variable, expression);
+                // TODO: add support for early termination
+                let _res = self.enforce_return_statement(cs, scope, statements, return_types);
             }
             Statement::For(index, start, stop, statements) => {
                 self.enforce_for_statement(cs, scope, index, start, stop, statements);
             }
-            Statement::Return(statements) => {
+            Statement::MultipleDefinition(assignees, function) => {
-                // TODO: add support for early termination
+                self.enforce_multiple_definition_statement(cs, scope, assignees, function);
-                let _res = self.enforce_return_statement(cs, scope, statements, return_types);
+            }
+            Statement::Definition(variable, expression) => {
+                self.enforce_definition_statement(cs, scope, variable, expression);
             }
         };
     }

program/src/leo.pest

@@ -76,6 +76,8 @@ protected_name = { visibility | value_boolean | "return" }
 //             "def" | "in" | "return" | "struct" | "true" }
 
 variable = @{ ((!protected_name ~ ASCII_ALPHA) | (protected_name ~ (ASCII_ALPHANUMERIC | "_"))) ~ (ASCII_ALPHANUMERIC | "_")* }
+optionally_typed_variable = { (variable) | (ty ~ variable) }
+optionally_typed_variable_tuple = _{ optionally_typed_variable ~ ("," ~ optionally_typed_variable)* }
 expression_primitive = { value | variable }
 
 /// Access
@@ -139,14 +141,16 @@ expression_tuple = _{ (expression ~ ("," ~ expression)*)? }
 
 /// Statements
 
-statement_assign = { assignee ~ "=" ~ expression }
-statement_definition = { ty ~ variable ~ "=" ~ expression }
 statement_return = { "return" ~ expression_tuple }
 statement_for = { "for" ~ variable ~ "in" ~ expression ~ ".." ~ expression ~ "do" ~ NEWLINE* ~ statement* ~ "endfor"}
+statement_multiple_assignment = { optionally_typed_variable_tuple ~ "=" ~  variable ~ "(" ~ expression_tuple ~ ")" }
+statement_definition = { ty ~ variable ~ "=" ~ expression }
+statement_assign = { assignee ~ "=" ~ expression }
 
 statement = {
     (statement_return
     | (statement_for
+      | statement_multiple_assignment
       | statement_definition
       | statement_assign
       ) ~ NEWLINE
@@ -159,7 +163,7 @@ parameter = {variable ~ ":" ~ visibility? ~ ty}
 parameter_list = _{(parameter ~ ("," ~ parameter)*)?}
 
 function_name = @{ ((!protected_name ~ ASCII_ALPHA) | (protected_name ~ (ASCII_ALPHANUMERIC | "_"))) ~ (ASCII_ALPHANUMERIC | "_")* }
-function_definition = {"function" ~ function_name ~ "(" ~ parameter_list ~ ")" ~ "->" ~ "(" ~ type_list ~ ")" ~ "{" ~ NEWLINE* ~ statement* ~ "}"}
+function_definition = {"function" ~ function_name ~ "(" ~ parameter_list ~ ")" ~ "->" ~ "(" ~ type_list ~ ")" ~ "{" ~ NEWLINE* ~ statement* ~ NEWLINE* ~ "}" ~ NEWLINE* }
 
 /// Utilities
 

program/src/lib.rs

@@ -1,10 +1,12 @@
 //! Module containing structs and types that make up an Leo program.
 
 extern crate from_pest;
-#[macro_use] extern crate lazy_static;
+#[macro_use]
+extern crate lazy_static;
 extern crate pest;
 extern crate pest_ast;
-#[macro_use] extern crate pest_derive;
+#[macro_use]
+extern crate pest_derive;
 
 pub mod ast;
 

program/src/types.rs

@@ -86,7 +86,7 @@ pub enum Expression<F: Field + PrimeField> {
     StructMemberAccess(Box<Expression<F>>, Variable<F>), // (struct name, struct member name)
 
     // Functions
-    FunctionCall(Box<Expression<F>>, Vec<Expression<F>>),
+    FunctionCall(Variable<F>, Vec<Expression<F>>),
 }
 
 /// Definition assignee: v, arr[0..2], Point p.x
@@ -101,9 +101,10 @@ pub enum Assignee<F: Field + PrimeField> {
 #[derive(Clone)]
 pub enum Statement<F: Field + PrimeField> {
     // Declaration(Variable),
+    Return(Vec<Expression<F>>),
     Definition(Assignee<F>, Expression<F>),
     For(Variable<F>, Integer, Integer, Vec<Statement<F>>),
-    Return(Vec<Expression<F>>),
+    MultipleDefinition(Vec<Assignee<F>>, Expression<F>),
 }
 
 /// Explicit type used for defining struct members and function parameters

program/src/types_display.rs

@@ -141,8 +141,24 @@ impl<F: Field + PrimeField> fmt::Display for Assignee<F> {
 impl<F: Field + PrimeField> fmt::Display for Statement<F> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
-            Statement::Definition(ref variable, ref statement) => {
+            Statement::Return(ref statements) => {
-                write!(f, "{} = {}", variable, statement)
+                write!(f, "return ")?;
+                for (i, value) in statements.iter().enumerate() {
+                    write!(f, "{}", value)?;
+                    if i < statements.len() - 1 {
+                        write!(f, ", ")?;
+                    }
+                }
+                write!(f, "\n")
+            }
+            Statement::MultipleDefinition(ref assignees, ref function) => {
+                for (i, id) in assignees.iter().enumerate() {
+                    write!(f, "{}", id)?;
+                    if i < assignees.len() - 1 {
+                        write!(f, ", ")?;
+                    }
+                }
+                write!(f, " = {}", function)
             }
             Statement::For(ref var, ref start, ref stop, ref list) => {
                 write!(f, "for {} in {}..{} do\n", var, start, stop)?;
@@ -151,11 +167,8 @@ impl<F: Field + PrimeField> fmt::Display for Statement<F> {
                 }
                 write!(f, "\tendfor")
             }
-            Statement::Return(ref statements) => {
+            Statement::Definition(ref variable, ref statement) => {
-                statements.iter().for_each(|statement| {
+                write!(f, "{} = {}", variable, statement)
-                    write!(f, "return {}", statement).unwrap();
-                });
-                write!(f, "\n")
             }
         }
     }
@@ -164,8 +177,24 @@ impl<F: Field + PrimeField> fmt::Display for Statement<F> {
 impl<F: Field + PrimeField> fmt::Debug for Statement<F> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
-            Statement::Definition(ref variable, ref statement) => {
+            Statement::Return(ref statements) => {
-                write!(f, "{} = {}", variable, statement)
+                write!(f, "return ")?;
+                for (i, value) in statements.iter().enumerate() {
+                    write!(f, "{}", value)?;
+                    if i < statements.len() - 1 {
+                        write!(f, ", ")?;
+                    }
+                }
+                write!(f, "\n")
+            }
+            Statement::MultipleDefinition(ref assignees, ref function) => {
+                for (i, id) in assignees.iter().enumerate() {
+                    write!(f, "{}", id)?;
+                    if i < assignees.len() - 1 {
+                        write!(f, ", ")?;
+                    }
+                }
+                write!(f, " = {}()", function)
             }
             Statement::For(ref var, ref start, ref stop, ref list) => {
                 write!(f, "for {:?} in {:?}..{:?} do\n", var, start, stop)?;
@@ -174,11 +203,8 @@ impl<F: Field + PrimeField> fmt::Debug for Statement<F> {
                 }
                 write!(f, "\tendfor")
             }
-            Statement::Return(ref statements) => {
+            Statement::Definition(ref variable, ref statement) => {
-                statements.iter().for_each(|statement| {
+                write!(f, "{} = {}", variable, statement)
-                    write!(f, "return {}", statement).unwrap();
-                });
-                write!(f, "\n")
             }
         }
     }

program/src/types_from.rs

@@ -205,8 +205,8 @@ impl<'ast, F: Field + PrimeField> From<ast::PostfixExpression<'ast>> for types::
             .into_iter()
             .fold(variable, |acc, access| match access {
                 ast::Access::Call(function) => match acc {
-                    types::Expression::Variable(_) => types::Expression::FunctionCall(
+                    types::Expression::Variable(variable) => types::Expression::FunctionCall(
-                        Box::new(acc),
+                        variable,
                         function
                             .expressions
                             .into_iter()
@@ -345,24 +345,6 @@ impl<'ast, F: Field + PrimeField> From<ast::Assignee<'ast>> for types::Assignee<
 
 /// pest ast -> types::Statement
 
-impl<'ast, F: Field + PrimeField> From<ast::AssignStatement<'ast>> for types::Statement<F> {
-    fn from(statement: ast::AssignStatement<'ast>) -> Self {
-        types::Statement::Definition(
-            types::Assignee::from(statement.assignee),
-            types::Expression::from(statement.expression),
-        )
-    }
-}
-
-impl<'ast, F: Field + PrimeField> From<ast::DefinitionStatement<'ast>> for types::Statement<F> {
-    fn from(statement: ast::DefinitionStatement<'ast>) -> Self {
-        types::Statement::Definition(
-            types::Assignee::from(statement.variable),
-            types::Expression::from_type(statement.ty, statement.expression),
-        )
-    }
-}
-
 impl<'ast, F: Field + PrimeField> From<ast::ReturnStatement<'ast>> for types::Statement<F> {
     fn from(statement: ast::ReturnStatement<'ast>) -> Self {
         types::Statement::Return(
@@ -399,13 +381,56 @@ impl<'ast, F: Field + PrimeField> From<ast::ForStatement<'ast>> for types::State
     }
 }
 
+impl<'ast, F: Field + PrimeField> From<ast::MultipleAssignmentStatement<'ast>>
+    for types::Statement<F>
+{
+    fn from(statement: ast::MultipleAssignmentStatement<'ast>) -> Self {
+        let assignees = statement
+            .assignees
+            .into_iter()
+            .map(|i| types::Assignee::Variable(types::Variable::from(i.id)))
+            .collect();
+
+        types::Statement::MultipleDefinition(
+            assignees,
+            types::Expression::FunctionCall(
+                types::Variable::from(statement.function_name),
+                statement
+                    .arguments
+                    .into_iter()
+                    .map(|e| types::Expression::from(e))
+                    .collect(),
+            ),
+        )
+    }
+}
+
+impl<'ast, F: Field + PrimeField> From<ast::AssignStatement<'ast>> for types::Statement<F> {
+    fn from(statement: ast::AssignStatement<'ast>) -> Self {
+        types::Statement::Definition(
+            types::Assignee::from(statement.assignee),
+            types::Expression::from(statement.expression),
+        )
+    }
+}
+
+impl<'ast, F: Field + PrimeField> From<ast::DefinitionStatement<'ast>> for types::Statement<F> {
+    fn from(statement: ast::DefinitionStatement<'ast>) -> Self {
+        types::Statement::Definition(
+            types::Assignee::from(statement.variable),
+            types::Expression::from_type(statement.ty, statement.expression),
+        )
+    }
+}
+
 impl<'ast, F: Field + PrimeField> From<ast::Statement<'ast>> for types::Statement<F> {
     fn from(statement: ast::Statement<'ast>) -> Self {
         match statement {
+            ast::Statement::Return(statement) => types::Statement::from(statement),
+            ast::Statement::Iteration(statement) => types::Statement::from(statement),
+            ast::Statement::MultipleAssignment(statement) => types::Statement::from(statement),
             ast::Statement::Assign(statement) => types::Statement::from(statement),
             ast::Statement::Definition(statement) => types::Statement::from(statement),
-            ast::Statement::Iteration(statement) => types::Statement::from(statement),
-            ast::Statement::Return(statement) => types::Statement::from(statement),
         }
     }
 }