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use proc_macro::{self, TokenStream};
use quote::quote;
use syn::parse::{Parse, ParseStream, Result};
use syn::punctuated::Punctuated;
use syn::{parse_macro_input, Expr, Token};
type Delimited<T> = Punctuated<T, Token![,]>;
type Vector = Delimited<Expr>;
type Matrix = Punctuated<Vector, Token![;]>;
struct Input {
matrix: Matrix,
}
impl Parse for Input {
fn parse(input: ParseStream) -> Result<Self> {
let matrix = Matrix::parse_terminated_with(input, Vector::parse_separated_nonempty)?;
Ok(Self { matrix })
}
}
impl Input {
fn into_rows(self) -> Vec<Vec<Expr>> {
self.matrix
.into_iter()
.map(|vector| vector.into_iter().collect())
.collect()
}
}
#[proc_macro]
pub fn matrix(input: TokenStream) -> TokenStream {
let rows = parse_macro_input!(input as Input).into_rows();
let n = rows.first().map_or(0, Vec::len);
let columns: Delimited<_> = (0..n)
.map(|column| {
let column: Vector = rows
.iter()
.filter_map(|row| row.get(column))
.cloned()
.collect();
quote! { [ #column ] }
})
.collect();
TokenStream::from(quote! { [ #columns ] })
}