mers rewrite is starting to be usable

mers_lib/src/program/run/chain.rs

@@ -1,8 +1,8 @@
-use std::{any::Any, sync::Arc};
+use std::sync::Arc;
 
-use crate::data::{function::Function, Data};
+use crate::data::{Data, Type};
 
-use super::MersStatement;
+use super::{CheckError, MersStatement};
 
 #[derive(Debug)]
 pub struct Chain {
@@ -10,6 +10,37 @@ pub struct Chain {
     pub chained: Box<dyn MersStatement>,
 }
 impl MersStatement for Chain {
+    fn check_custom(
+        &self,
+        info: &mut super::CheckInfo,
+        init_to: Option<&Type>,
+    ) -> Result<Type, CheckError> {
+        if init_to.is_some() {
+            return Err(CheckError("can't init to statement type Chain".to_string()));
+        }
+        let arg = self.first.check(info, None)?;
+        let func = self.chained.check(info, None)?;
+        let mut o = Type::empty();
+        for func in &func.types {
+            if let Some(func) = func
+                .as_any()
+                .downcast_ref::<crate::data::function::FunctionT>()
+            {
+                match (func.0)(&arg) {
+                    Ok(t) => o.add(Arc::new(t)),
+                    Err(e) =>
+                    return Err(CheckError(format!(
+                        "cannot run this function with this argument (type: {arg}), because it would cause the following error:\n{e}"
+                    ))),
+                }
+            } else {
+                return Err(CheckError(format!(
+                    "cannot chain with a non-function ({func})"
+                )));
+            }
+        }
+        Ok(o)
+    }
     fn run_custom(&self, info: &mut super::Info) -> Data {
         let f = self.first.run(info);
         let c = self.chained.run(info);