Implement pest CSV demo

https://pest.rs/book/examples/csv.html

Cargo.toml

@@ -7,3 +7,5 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+pest = "2.6.0"
+pest_derive = "2.6.0"

demo/demo.csv

@@ -0,0 +1,5 @@
+65279,1179403647,1463895090
+3.1415927,2.7182817,1.618034
+-40,-273.15
+13,42
+65537

demo/src/main.rs

@@ -1,5 +1,5 @@
 use renrs;
 
 fn main() {
-    renrs::hello();
+    renrs::parse("demo.csv");
 }

src/csv.pest

@@ -0,0 +1,9 @@
+// + indicates one or more times
+field = { (ASCII_DIGIT | "." | "-")+ }
+// ~ indicates directly followed by
+// * indicates zero or more times (optional)
+record = { field ~ ("," ~ field)* }
+// SOI - start of input
+// END - end of input
+// There may be trailing newlines at the end
+file = { SOI ~ (record ~ ("\r\n" | "\n"))* ~ "\n"* ~ EOI }

src/lib.rs

@@ -1,3 +1,35 @@
-pub fn hello() {
-    println!("Hello, world!");
+use std::fs;
+
+use pest::Parser;
+use pest_derive::Parser;
+
+#[derive(Parser)]
+#[grammar = "csv.pest"]
+struct CSVParser;
+
+pub fn parse(file_path: &str) {
+    let unparsed_file = fs::read_to_string(file_path).expect("cannot find file");
+    let file = CSVParser::parse(Rule::file, &unparsed_file)
+        .expect("unsuccessful parse") // unwrap the parse result
+        .next().unwrap(); // get and unwrap the `file` rule; never fails
+
+    let mut field_sum = 0.0;
+    let mut record_count: u64 = 0;
+
+    for record in file.into_inner() {
+        match record.as_rule() {
+            Rule::record => {
+                record_count += 1;
+
+                for field in record.into_inner() {
+                    field_sum += field.as_str().parse::<f64>().unwrap();
+                }
+            },
+            Rule::EOI => (),
+            _ => unreachable!(),
+        }
+    }
+
+    println!("Sum of fields: {field_sum}");
+    println!("Number of records: {record_count}");
 }