fix negative fields, add test for them

compiler/src/value/field/field_type.rs

@@ -40,6 +40,8 @@ use snarkvm_models::{
 use std::{borrow::Borrow, cmp::Ordering};
 
 #[derive(Clone, Debug)]
+// Isn't this redudant?
+// PrimeField already implements Field.
 pub enum FieldType<F: Field + PrimeField> {
     Constant(F),
     Allocated(FpGadget<F>),
@@ -54,7 +56,22 @@ impl<F: Field + PrimeField> FieldType<F> {
     }
 
     pub fn constant(string: String, span: &Span) -> Result<Self, FieldError> {
-        let value = F::from_str(&string).map_err(|_| FieldError::invalid_field(string, span.to_owned()))?;
+        let first_char = string.chars().next().unwrap();
+        let new_string: &str;
+        let value;
+
+        // Check if first symbol is a negative.
+        // If so strip it, parse rest of string and then negate it.
+        if first_char == '-' {
+            new_string = string
+                .chars()
+                .next()
+                .map(|c| &string[c.len_utf8()..])
+                .ok_or(FieldError::invalid_field(string.clone(), span.to_owned()))?;
+            value = -F::from_str(&new_string).map_err(|_| FieldError::invalid_field(string, span.to_owned()))?;
+        } else {
+            value = F::from_str(&string).map_err(|_| FieldError::invalid_field(string, span.to_owned()))?;
+        }
 
         Ok(FieldType::Constant(value))
     }

compiler/tests/field/mod.rs

@@ -66,6 +66,14 @@ fn test_negate() {
     }
 }
 
+#[test]
+fn test_negative_declaration() {
+    let program_string = include_str!("negative_declaration.leo");
+    let mut program = parse_program(program_string).unwrap();
+
+    assert_satisfied(program)
+}
+
 #[test]
 fn test_add() {
     use std::ops::Add;

compiler/tests/field/negative_declaration.leo

@@ -0,0 +1,3 @@
+function main() {
+    let negOneField: field = -1field;
+}

compiler/tests/input_files/program_input/input/main_field.in

@@ -0,0 +1,2 @@
+[main]
+a: field = 1;

compiler/tests/input_files/program_input/main_field.leo

@@ -0,0 +1,4 @@
+function main(a: field) {
+    // Change to assert when == is implemented for field.
+    console.log("a: {}", a);
+}

compiler/tests/input_files/program_input/mod.rs

@@ -93,3 +93,13 @@ fn test_input_array_dimensions_mismatch() {
 
     expect_fail(program);
 }
+
+#[test]
+fn test_field_input() {
+    let program_string = include_str!("main_field.leo");
+    let input_string = include_str!("input/main_field.in");
+
+    let program = parse_program_with_input(program_string, input_string).unwrap();
+
+    assert_satisfied(program);
+}