Adds [constants] section to input file:

```
[constants]
x: bool = true; // will be constant in program
y: u32 = 100;
```

ast/src/input/program_input/main_input.rs

@@ -56,18 +56,29 @@ impl MainInput {
         self.input.insert(key, value);
     }
 
+    pub fn insert_constant(&mut self, key: String, value: Option<InputValue>) {
+        self.constants.insert(key, value);
+    }
+
     /// Parses main input definitions and stores them in `self`.
     pub fn parse(&mut self, definitions: Vec<Definition>) -> Result<(), InputParserError> {
         for definition in definitions {
             let name = definition.parameter.variable.value;
-            let is_const = definition.const_.is_some();
             let value = InputValue::from_expression(definition.parameter.type_, definition.expression)?;
 
-            if is_const {
-                self.constants.insert(name, Some(value));
-            } else {
-                self.input.insert(name, Some(value));
+            self.insert(name, Some(value));
         }
+
+        Ok(())
+    }
+
+    /// Parses constants input definitions and stores them in `self`.
+    pub fn parse_constants(&mut self, definitions: Vec<Definition>) -> Result<(), InputParserError> {
+        for definition in definitions {
+            let name = definition.parameter.variable.value;
+            let value = InputValue::from_expression(definition.parameter.type_, definition.expression)?;
+
+            self.insert_constant(name, Some(value));
         }
 
         Ok(())

ast/src/input/program_input/program_input.rs

@@ -58,6 +58,7 @@ impl ProgramInput {
     /// Parse each input included in a file and store them in `self`.
     pub fn parse(&mut self, section: Section) -> Result<(), InputParserError> {
         match section.header {
+            Header::Constants(_constants) => self.main.parse_constants(section.definitions),
             Header::Main(_main) => self.main.parse(section.definitions),
             Header::Registers(_registers) => self.registers.parse(section.definitions),
             header => Err(InputParserError::input_section_header(header)),

input/src/definitions/definition.rs

@@ -14,7 +14,6 @@
 // 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/>.
 
-use super::Const;
 use crate::{ast::Rule, common::LineEnd, expressions::Expression, parameters::Parameter};
 
 use pest::Span;
@@ -23,17 +22,9 @@ use pest_ast::FromPest;
 #[derive(Clone, Debug, FromPest, PartialEq)]
 #[pest_ast(rule(Rule::definition))]
 pub struct Definition<'ast> {
-    pub const_: Option<Const<'ast>>,
     pub parameter: Parameter<'ast>,
     pub expression: Expression<'ast>,
     pub line_end: LineEnd,
     #[pest_ast(outer())]
     pub span: Span<'ast>,
 }
-
-impl<'ast> Definition<'ast> {
-    /// Check whether `const` keyword is placed before definition.
-    pub fn is_const(&self) -> bool {
-        self.const_.is_some()
-    }
-}

input/src/definitions/mod.rs

@@ -16,6 +16,3 @@
 
 pub mod definition;
 pub use definition::*;
-
-pub mod const_;
-pub use const_::*;

input/src/leo-input.pest

@@ -210,19 +210,19 @@ registers = { "registers" }
 // Declared in sections/state.rs
 state = { "state" }
 
+// Declared in sections/constants.rs
+constants = { "constants" }
+
 // Declared in sections/state_leaf.rs
 state_leaf = { "state_leaf" }
 
 // Declared in sections/header.rs
-header = { main | record | registers | state_leaf | state | identifier }
+header = { main | constants | record | registers | state_leaf | state | identifier }
 
 /// Definitions
 
-// Declared in definition/const_modifier.rs
-const_ = { "const" }
-
 // Declared in definition/definition.rs
-definition = { const_? ~ parameter ~ "=" ~ expression ~ LINE_END }
+definition = {  parameter ~ "=" ~ expression ~ LINE_END }
 
 /// Table
 

input/src/sections/constants.rs

@@ -20,8 +20,8 @@ use pest::Span;
 use pest_ast::FromPest;
 
 #[derive(Clone, Debug, FromPest, PartialEq)]
-#[pest_ast(rule(Rule::const_))]
-pub struct Const<'ast> {
+#[pest_ast(rule(Rule::constants))]
+pub struct Constants<'ast> {
     #[pest_ast(outer())]
     pub span: Span<'ast>,
 }

input/src/sections/header.rs

@@ -17,7 +17,7 @@
 use crate::{
     ast::Rule,
     common::Identifier,
-    sections::{Main, Record, Registers, State, StateLeaf},
+    sections::{Constants, Main, Record, Registers, State, StateLeaf},
 };
 
 use pest::Span;
@@ -27,6 +27,7 @@ use std::fmt;
 #[derive(Clone, Debug, FromPest, PartialEq)]
 #[pest_ast(rule(Rule::header))]
 pub enum Header<'ast> {
+    Constants(Constants<'ast>),
     Main(Main<'ast>),
     Record(Record<'ast>),
     Registers(Registers<'ast>),
@@ -38,6 +39,7 @@ pub enum Header<'ast> {
 impl<'ast> Header<'ast> {
     pub fn span(self) -> Span<'ast> {
         match self {
+            Header::Constants(constants) => constants.span,
             Header::Main(main) => main.span,
             Header::Record(record) => record.span,
             Header::Registers(registers) => registers.span,
@@ -51,6 +53,7 @@ impl<'ast> Header<'ast> {
 impl<'ast> fmt::Display for Header<'ast> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self {
+            Header::Constants(_constants) => write!(f, "constants"),
             Header::Main(_main) => write!(f, "main"),
             Header::Record(_record) => write!(f, "record"),
             Header::Registers(_registers) => write!(f, "registers"),

input/src/sections/mod.rs

@@ -14,6 +14,9 @@
 // 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 constants;
+pub use constants::*;
+
 pub mod header;
 pub use header::*;