Clean up fac! noise as literal

README.md

@@ -53,10 +53,10 @@ let factor = fac![res, X(0)];
 graph.add_factor(factor);
 
 let res = BetweenResidual::new(y.minus(&x));
-let noise = GaussianNoise::from_scalar_sigma(0.1);
 let robust = Huber::default();
-let factor = fac![res, (X(0), X(1)), noise, robust];
+let factor = fac![res, (X(0), X(1)), 0.1 as std, robust];
 // The same as above, but verbose
+// let noise = GaussianNoise::from_scalar_sigma(0.1);
 // let factor = FactorBuilder::new2(res, X(0), X(1))
 //     .noise(noise)
 //     .robust(robust)

factrs-proc/src/fac.rs

@@ -1,7 +1,9 @@
 use proc_macro2::Span;
 use proc_macro2::TokenStream as TokenStream2;
 use quote::quote;
+use quote::ToTokens;
 use syn::parse_quote;
+use syn::ExprCast;
 use syn::{parse::Parse, punctuated::Punctuated, Expr, Ident, Token};
 
 pub struct Factor {
@@ -76,10 +78,16 @@ impl Parse for Factor {
 
         // Then the noise
         let noise = if input.len() >= 3 {
+            let m = quote!(factrs::noise);
             match &input[2] {
-                Expr::Lit(l) => {
-                    Some(parse_quote!(factrs::noise::GaussianNoise::from_scalar_sigma(#l)))
+                Expr::Cast(ExprCast { expr, ty, .. }) => {
+                    match ty.to_token_stream().to_string().as_str() {
+                        "std" => Some(parse_quote!(#m::GaussianNoise::from_scalar_sigma(#expr))),
+                        "cov" => Some(parse_quote!(#m::GaussianNoise::from_scalar_cov(#expr))),
+                        _ => return Err(syn::Error::new_spanned(ty, "Unknown cast for noise")),
+                    }
                 }
+                Expr::Infer(_) => Some(parse_quote!(#m::UnitNoise)),
                 _ => Some(input[2].clone()),
             }
         } else {

src/residuals/imu_preint/residual.rs

@@ -396,9 +396,9 @@ mod test {
         // Build factor and graph
         let mut graph = Graph::new();
         let factor = preint.build(X(0), V(0), B(0), X(1), V(1), B(1));
-        let prior_x0 = fac!(PriorResidual::new(x0.clone()), X(0), 1e-3);
-        let prior_v0 = fac!(PriorResidual::new(v0.clone()), V(0), 1e-3);
-        let prior_b0 = fac!(PriorResidual::new(b0.clone()), B(0), 1e-3);
+        let prior_x0 = fac!(PriorResidual::new(x0.clone()), X(0), 1e-3 as cov);
+        let prior_v0 = fac!(PriorResidual::new(v0.clone()), V(0), 1e-3 as cov);
+        let prior_b0 = fac!(PriorResidual::new(b0.clone()), B(0), 1e-3 as cov);
         graph.add_factor(factor);
         graph.add_factor(prior_x0);
         graph.add_factor(prior_v0);