Parsing len and sampling frequency works

firls-rs-macros/src/lib.rs

@@ -1,16 +1,65 @@
 extern crate proc_macro;
 use proc_macro::TokenStream;
-use syn::parse::{Parse, ParseStream};
+use syn::parse::{Parse, ParseStream, Parser};
 use syn::parse_macro_input;
-use syn::{punctuated::Punctuated, Expr, Token};
+use syn::spanned::Spanned;
+use syn::{punctuated::Punctuated, Expr, Lit, Token};
 
-struct FirlsRealInput {}
+struct FirlsRealInput {
+    filter_len: usize,
+    sample_frequency: f32,
+}
 
 impl Parse for FirlsRealInput {
     fn parse(input: ParseStream) -> Result<Self, syn::Error> {
         let arg_list = Punctuated::<Expr, Token![,]>::parse_separated_nonempty(input)?;
 
-        Ok(FirlsRealInput {})
+        if arg_list.len() != 3 {
+            return Err(syn::Error::new(
+                arg_list.span(),
+                "firls_real takes 3 parameters",
+            ));
+        }
+
+        let filter_len = parse_filter_len(&arg_list[0])?;
+        let sample_frequency = parse_frequency(&arg_list[1])?;
+
+        Ok(FirlsRealInput {
+            filter_len,
+            sample_frequency,
+        })
+    }
+}
+
+fn parse_filter_len(len: &Expr) -> Result<usize, syn::Error> {
+    match len {
+        Expr::Lit(expr) => match &expr.lit {
+            Lit::Int(int_lit) => int_lit.base10_parse(),
+            _ => Err(syn::Error::new(
+                expr.span(),
+                "expected integer literal for len",
+            )),
+        },
+        _ => Err(syn::Error::new(
+            len.span(),
+            "len should be a literal expression",
+        )),
+    }
+}
+
+fn parse_frequency(freq: &Expr) -> Result<f32, syn::Error> {
+    match freq {
+        Expr::Lit(expr) => match &expr.lit {
+            Lit::Float(float_lit) => float_lit.base10_parse(),
+            _ => Err(syn::Error::new(
+                expr.span(),
+                "expected float literal for frequency",
+            )),
+        },
+        _ => Err(syn::Error::new(
+            freq.span(),
+            "frequency should be a literal expression",
+        )),
     }
 }