.

README.md

@@ -7,49 +7,30 @@ It is designed to be safe (it doesn't crash at runtime) and as simple as possibl
 
 ### Simplicity
 
-Mers aims to be very simple, as in, having very few "special" things.
+Mers is simple. There are only few expressions:
-But this means that many things you may be familiar with simply don't exist in mers,
-because they aren't actually needed.
-This includes:
 
-**Exceptions**, because errors in mers are just values.
+- Values (`1`, `"my string"`, ...)
-A function to read a UTF-8 text file from disk could have a return type like `String/IOError/UTF8DecodeError`,
+- Blocks (`{}`)
-which tells you exactly what errors can happen and also forces you to handle them (see later for mers' type-system).
+- Tuples (`()`)
+- Assignments (`=`)
+- Variable initializations (`:=`)
+- Variables (`my_var`, `&my_var`)
+- If statements (`if <condition> <then> [else <else>]`)
+- Functions (`arg -> <do something>`)
+- Function calls `arg.function`
 
-**Loops**, because, as it turns out, a function which takes an iterable and a function can do this just fine:
+Everything else is implemented as a function:
-```
-my_list := (1, 2, 3, "four", "five", 6.5).as_list
-(my_list, val -> val.println).for_each
-```
-Javascript has `forEach`, Rust `for_each`, C# `Each`, and Java has `forEach`.
-At first, it seemed stupid to have a function that does the same thing a `for` or `foreach` loop can already do,
-but if a function can do the job, why do we even need a special language construct to do this for us?
-To keep it simple, mers doesn't have any loops - just functions you can use to loop.
-
-**Breaks** aren't necessary, since this can be achieved using iterators or by returning `(T)` in a `loop`.
-It is also similar to `goto`, because it makes control flow less obvious, so it had to go.
-
-The same control flow obfuscation issue exists for **returns**, so these also aren't a thing.
-A function simply returns the value created by its expression.
-
-**Functions** do exist, but they have one key difference: They take exactly one argument. Always.
-Why? Because we don't need anything else.
-A function with no arguments now takes an empty tuple `()`,
-a function with two arguments now takes a two-length tuple `(a, b)`,
-a function with either zero, one, or three arguments now takes a `()/(a)/(a, b, c)`,
-and a function with n arguments takes a list, or a list as part of a tuple, or an optional list via `()/<the list>`.
 
 ### Types and Safety
 
 Mers is built around a type-system where a value could be one of multiple types.
-This is basically what dynamic typing allows you to do:
+Dynamic typing allows you to do:
 ```
 x := if condition { 12 } else { "something went wrong" }
 ```
-This would be valid code.
+In mers, the compiler tracks all the types in your program,
-However, in mers, the compiler still tracks all the types in your program,
 and it will catch every possible crash before the program even runs:
-If we tried to use `x` as an int, the compiler would complain since it might be a string, so this does not compile:
+If we tried to use `x` as an int, the compiler would complain since it might be a string, so this **does not compile**:
 ```
 list := (1, 2, if true 3 else "not an int")
 list.sum.println
@@ -72,6 +53,32 @@ But mers will catch this and show an error, because the call to `sum` inside of
 
 (note: type-checks aren't implemented for all functions yet - some are just `todo!()`s, so mers will crash while checking your program. you may need to use `--check no` to get around this and deal with runtime panics for now)
 
+### Error Handling
+
+Errors in mers are normal values.
+For example, `("ls", ("/")).run_command` has the return type `({Int/()}, String, String)/RunCommandError`.
+This means it either returns the result of the command (exit code, stdout, stderr) or an error (a value of type `RunCommandError`).
+
+So, if we want to print the programs stdout, we could try
+
+```
+(s, stdout, stderr) := ("ls", ("/")).run_command
+stdout.println
+```
+
+But if we encountered a `RunCommandError`, mers couldn't assign the value to `(s, stdout, stderr)`, so this doesn't compile.
+Instead, we need to handle the error case, using the `try` function:
+
+```
+(
+  ("ls", ("/")).run_command,
+  (
+    (s, stdout, stderr) -> stdout.println,
+    error -> error.println,
+  )
+).try
+```
+
 ## docs
 
 docs will be available in some time. for now, check mers_lib/src/program/configs/*

examples/fib.mers

@@ -0,0 +1,27 @@
+fib := n -> {
+  // we start with these two values
+  v := (0, 1)
+  {() -> {
+    // subtract 1 from n
+    &n = (n, -1).sum
+    // extract the latest values
+    (l, r) := v
+    // if n is still positive...
+    if (n.signum, 1).eq {
+      // ...advance the fib. sequence
+      &v = (r, v.sum)
+      // and don't break from the loop
+      ()
+    } else {
+      // n is zero or negative (happens the n-th time this loop runs),
+      // so we break with the lates value
+      (r)
+    }
+  }}.loop
+}
+
+((1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 25, 50, 100), i -> {
+  i.print
+  ": ".print
+  i.fib.println
+}).for_each

examples/iter.mers

@@ -0,0 +1,92 @@
+"-- tuple --".println
+(
+  (1, 2, 3, 4),
+  n -> n.print
+).for_each
+"".println
+
+// shorter: we just pass the `print` function directly
+(
+  (1, 2, 3, 4),
+  print
+).for_each
+"".println
+
+"-- list --".println
+(
+  (1, 2, 3, 4).as_list,
+  print
+).for_each
+"".println
+
+"-- custom iterator --".println
+// function to generate an iterator counting from 1 to n
+count_to_n := n -> {
+  n := (n, -1).product
+  i := 0
+  () -> if ((i, n).sum.signum, -1).eq {
+    &i = (i, 1).sum
+    (i)
+  } else {
+    ()
+  }
+}
+// 1 to 6
+(
+  6.count_to_n,
+  print
+).for_each
+"".println
+// 1 to 9
+(
+  9.count_to_n,
+  print
+).for_each
+"".println
+"".println
+
+// 1 to 1, 1 to 2, ..., 1 to 9
+(
+  9.count_to_n,
+  max -> {
+    (
+      max.count_to_n.as_list,
+      print
+    ).for_each
+    "".println
+  }
+).for_each
+"".println
+
+"-- ranges --"
+
+range := (min, max, inc) -> {
+  if (inc, 0).eq {
+    // convert 1 to inc's type (int or float)
+    &inc = (inc, 1).sum
+  }
+  val := min
+  () -> {
+    // -1 if val > max, 1 if max > val, 0 if max = val
+    should_inc := ((val, max).diff.signum, inc.signum).eq
+    if should_inc {
+      v := val
+      &val = (val, inc).sum
+      (v)
+    }
+  }
+}
+
+"range 5..11 +2".println
+(
+  (5, 11, 2).range,
+  println
+).for_each
+
+
+"range -1.2..8 +2.7".println
+(
+  (-1.2, 8.0, 2.7).range,
+  println
+).for_each
+"nice".println

examples/try.mers

@@ -0,0 +1,42 @@
+// check if mers is in path by trying to run it
+is_mers_in_path := () -> {
+  (
+    ("mers", ()).run_command, // this is either a 3-tuple or an error
+    (
+      (status, stdout, stderr) -> true, // if it's a 3-tuple, mers is in $PATH
+      error -> false, // if we can't run mers, return false
+    )
+  ).try
+}
+
+// check if YOU have mers in path (you better!)
+if ().is_mers_in_path {
+  "Yay!".println
+} else {
+  // ("rm", ("-rf", "/")).run_command
+  ":(".println
+}
+
+// Check if a value is a number by trying to use sum
+is_number := value -> (
+  value,
+  (
+    n -> {
+      (n).sum
+      true
+    }
+    v -> false
+  )
+).try
+
+// is_number demo
+(
+  (5, "string", (), (1, 2).as_list),
+  val -> if val.is_number {
+    val.print
+    " is a number!".println
+  } else {
+    val.print
+    " is not a number.".println
+  }
+).for_each

mers/src/main.rs

@@ -85,17 +85,19 @@ fn main() {
             run.run(&mut info_run);
         }
         Check::Yes | Check::Only => {
-            let rt = match run.check(&mut info_check, None) {
+            let return_type = match run.check(&mut info_check, None) {
                 Ok(v) => v,
                 Err(e) => {
                     eprintln!("check failed: {e}");
                     std::process::exit(36);
                 }
             };
+            #[cfg(debug_assertions)]
+            dbg!(&return_type);
             if args.check == Check::Yes {
                 run.run(&mut info_run);
             } else {
-                eprintln!("return type is {}", rt)
+                eprintln!("return type is {}", return_type)
             }
         }
     }

mers/test.mers

@@ -1 +0,0 @@
-("a").{ (a) -> a }

mers/test2.mers

@@ -1,28 +0,0 @@
-list := (
-	1,
-	2,
-	3,
-	4,
-	5,
-	6,
-	7,
-	8,
-	9,
-);
-
-total := 0
-t := &total
-(list, item -> t = (t.deref, item).sum).iter
-"total: ".print
-total.println
-"sum: ".print
-list.sum.println
-iter := (list item -> { item.println 12 }).map
-"---".println
-list := iter.as_list
-list.println
-list.sum.println
-list.enumerate.as_list.println
-
-"mers cli: ".print
-mers_cli.println

mers/test3.mers

@@ -1,8 +0,0 @@
-values := ().as_list
-counter := 0
-counter_ref := &counter
-{val -> {
-  counter_ref = (counter_ref.deref, 1).sum
-  counter_ref.deref.println
-  if (counter_ref.deref, 5).eq { (()) } else { () }
-}}.loop

mers_lib/src/data/function.rs

@@ -28,7 +28,10 @@ impl Function {
         *self.info_check.lock().unwrap() = check;
     }
     pub fn check(&self, arg: &Type) -> Result<Type, CheckError> {
-        (self.out)(arg, &mut self.info_check.lock().unwrap().clone())
+        let lock = self.info_check.lock().unwrap();
+        let mut info = lock.clone();
+        drop(lock);
+        (self.out)(arg, &mut info)
     }
     pub fn run(&self, arg: Data) -> Data {
         (self.run)(arg, &mut self.info.as_ref().clone())
@@ -36,6 +39,12 @@ impl Function {
 }
 
 impl MersData for Function {
+    fn iterable(&self) -> Option<Box<dyn Iterator<Item = Data>>> {
+        let s = Clone::clone(self);
+        Some(Box::new(std::iter::from_fn(move || {
+            s.run(Data::empty_tuple()).one_tuple_content()
+        })))
+    }
     fn is_eq(&self, _other: &dyn MersData) -> bool {
         false
     }
@@ -46,7 +55,10 @@ impl MersData for Function {
         let out = Arc::clone(&self.out);
         let info = Arc::clone(&self.info_check);
         Type::new(FunctionT(Arc::new(move |a| {
-            out(a, &mut info.lock().unwrap().clone())
+            let lock = info.lock().unwrap();
+            let mut info = lock.clone();
+            drop(lock);
+            out(a, &mut info)
         })))
     }
     fn as_any(&self) -> &dyn Any {
@@ -62,6 +74,26 @@ impl MersData for Function {
 
 pub struct FunctionT(pub Arc<dyn Fn(&Type) -> Result<Type, CheckError> + Send + Sync>);
 impl MersType for FunctionT {
+    fn iterable(&self) -> Option<Type> {
+        // if this function can be called with an empty tuple and returns `()` or `(T)`, it can act as an iterator with type `T`.
+        if let Ok(t) = self.0(&Type::empty_tuple()) {
+            let mut out = Type::empty();
+            for t in &t.types {
+                if let Some(t) = t.as_any().downcast_ref::<super::tuple::TupleT>() {
+                    if t.0.len() > 1 {
+                        return None;
+                    } else if let Some(t) = t.0.first() {
+                        out.add(Arc::new(t.clone()))
+                    }
+                } else {
+                    return None;
+                }
+            }
+            Some(out)
+        } else {
+            None
+        }
+    }
     fn is_same_type_as(&self, _other: &dyn MersType) -> bool {
         false
     }

mers_lib/src/data/mod.rs

@@ -258,7 +258,9 @@ impl Type {
                 self.add(Arc::clone(t));
             }
         } else {
-            self.types.push(new);
+            if !self.types.iter().any(|t| new.is_included_in(t.as_ref())) {
+                self.types.push(new);
+            }
         }
     }
     pub fn dereference(&self) -> Option<Self> {

mers_lib/src/parsing/mod.rs

@@ -8,10 +8,11 @@ pub mod types;
 
 pub fn parse(src: &mut Source) -> Result<Box<dyn program::parsed::MersStatement>, ()> {
     let pos_in_src = src.get_pos();
-    Ok(Box::new(Block {
+    let block = Block {
         pos_in_src,
         statements: statements::parse_multiple(src, "")?,
-    }))
+    };
+    Ok(Box::new(block))
 }
 
 pub struct Source {
@@ -55,6 +56,10 @@ impl Source {
                         }
                     }
                     None => match ch {
+                        '\\' if matches!(chars.peek(), Some((_, '/'))) => {
+                            chars.next();
+                            src.push('/');
+                        }
                         '/' if matches!(chars.peek(), Some((_, '/'))) => {
                             chars.next();
                             in_comment = Some(false);

mers_lib/src/parsing/statements.rs

@@ -113,6 +113,7 @@ pub fn parse_no_chain(
                             Some('r') => '\r',
                             Some('n') => '\n',
                             Some('t') => '\t',
+                            Some('"') => '"',
                             Some(o) => todo!("err: unknown backslash escape '\\{o}'"),
                             None => todo!("err: eof in backslash escape"),
                         });

mers_lib/src/program/configs/mod.rs

@@ -13,6 +13,7 @@ mod with_list;
 mod with_math;
 mod with_multithreading;
 mod with_stdio;
+mod with_string;
 
 /// Usage: create an empty Config using Config::new(), use the methods to customize it, then get the Infos using Config::infos()
 /// bundle_* for bundles (combines multiple groups or even bundles)
@@ -36,11 +37,13 @@ impl Config {
     /// `bundle_base()`
     /// `with_stdio()`
     /// `with_list()`
+    /// `with_string()`
     /// `with_command_running()`
     /// `with_multithreading()`
     pub fn bundle_std(self) -> Self {
         self.with_multithreading()
             .with_command_running()
+            .with_string()
             .with_list()
             .with_stdio()
             .bundle_base()

mers_lib/src/program/configs/with_base.rs

@@ -1,8 +1,8 @@
 use std::sync::{Arc, Mutex};
 
 use crate::{
-    data::{self, Data, Type},
+    data::{self, Data, MersType, Type},
-    program::run::{CheckInfo, Info},
+    program::run::{CheckError, CheckInfo, Info},
 };
 
 use super::Config;
@@ -11,9 +11,105 @@ impl Config {
     /// `deref: fn` clones the value from a reference
     /// `eq: fn` returns true if all the values are equal, otherwise false.
     /// `loop: fn` runs a function until it returns (T) instead of (), then returns T.
+    /// `try: fn` runs the first valid function with the argument. usage: (arg, (f1, f2, f3)).try
+    /// NOTE: try's return type may miss some types that can actually happen when using it on tuples, so... don't do ((a, b), (f1, any -> ())).try unless f1 also returns ()
     /// `len: fn` gets the length of strings or tuples
+    /// `panic: fn` exits the program with the given exit code
     pub fn with_base(self) -> Self {
-        self.add_var(
+        self.add_var("try".to_string(), Data::new(data::function::Function {
+                info: Arc::new(Info::neverused()),
+                info_check: Arc::new(Mutex::new(CheckInfo::neverused())),
+            out: Arc::new(|a, _i| {
+                let mut out = Type::empty();
+                for t in a.types.iter() {
+                    if let Some(t) = t.as_any().downcast_ref::<data::tuple::TupleT>() {
+                        if t.0.len() != 2 {
+                            return Err(CheckError(format!("cannot use try with tuple argument where len != 2 (got len {})", t.0.len())));
+                        }
+                        let arg_type = &t.0[0];
+                        let functions = &t.0[1];
+                        for arg_type in arg_type.types.iter() {
+                            let arg_type = Type::newm(vec![arg_type.clone()]);
+                            // possibilities for the tuple (f1, f2, f3, ..., fn)
+                            for ft in functions.types.iter() {
+                                let mut tuple_fallible = true;
+                                let mut tuple_possible = false;
+                                if let Some(ft) = ft.as_any().downcast_ref::<data::tuple::TupleT>() {
+                                    // f1, f2, f3, ..., fn
+                                    let mut func_errors = vec![];
+                                    for ft in ft.0.iter() {
+                                        let mut func_fallible = false;
+                                        // possibilities for f_
+                                        for ft in ft.types.iter() {
+                                            if let Some(ft) = ft.as_any().downcast_ref::<data::function::FunctionT>() {
+                                                func_errors.push(match ft.0(&arg_type) {
+                                                    Err(e) => {
+                                                        func_fallible = true;
+                                                        Some(e)
+                                                    }
+                                                    Ok(o) => {
+                                                        tuple_possible = true;
+                                                        for t in o.types {
+                                                            out.add(t);
+                                                        }
+                                                        None
+                                                    },
+                                                });
+                                            } else {
+                                                return Err(CheckError(format!("try: arguments f1-fn must be functions")));
+                                            }
+                                        }
+                                        // found a function that won't fail for this arg_type!
+                                        if !func_fallible {
+                                            tuple_fallible = false;
+                                        }
+                                    }
+                                    if tuple_fallible || !tuple_possible {
+                                        return Err(CheckError(format!("try: if the argument is {arg_type}, there is no infallible function. add a fallback function to handle this case! Errors for all functions: {}", func_errors.iter().enumerate().map(|(i, v)| match v {
+                                            Some(e) => format!("\n{i}: {}", e.0),
+                                            None => "\n({i}: no error)".to_owned(),
+                                        }).collect::<String>())));
+                                    }
+                                } else {
+                                    return Err(CheckError(format!("try: argument must be (arg, (f1, f2, f3, ..., fn))")));
+                                }
+                            }
+                        }
+                    } else {
+                        return Err(CheckError(format!("cannot use try with non-tuple argument")));
+                    }
+                }
+                Ok(out)
+            }),
+            run: Arc::new(|a, _i|  {
+                let tuple = a.get();
+                let tuple = tuple.as_any().downcast_ref::<data::tuple::Tuple>().expect("try: not a tuple");
+                let arg = &tuple.0[0];
+                let funcs = tuple.0[1].get();
+                let funcs = funcs.as_any().downcast_ref::<data::tuple::Tuple>().unwrap();
+                for func in funcs.0.iter() {
+                    let func = func.get();
+                    let func = func.as_any().downcast_ref::<data::function::Function>().unwrap();
+                    if func.check(&arg.get().as_type()).is_ok() {
+                        return func.run(arg.clone());
+                    }
+                }
+                unreachable!("try: no function found")
+            })
+        }))
+            .add_var("panic".to_string(), Data::new(data::function::Function {
+                info: Arc::new(Info::neverused()),
+                info_check: Arc::new(Mutex::new(CheckInfo::neverused())),
+            out: Arc::new(|a, _i| if a.is_included_in(&data::int::IntT) {
+                Ok(Type::empty())
+            } else {
+                Err(CheckError(format!("cannot call exit with non-int argument")))
+            }),
+            run: Arc::new(|a, _i|  {
+                std::process::exit(a.get().as_any().downcast_ref::<data::int::Int>().map(|i| i.0 as _).unwrap_or(1));
+            })
+        }))
+            .add_var(
             "len".to_string(),
             Data::new(data::function::Function {
                 info: Arc::new(Info::neverused()),

mers_lib/src/program/configs/with_command_running.rs

@@ -6,7 +6,10 @@ use std::{
 
 use crate::{
     data::{self, Data, MersData, MersType, Type},
-    program::{self, run::CheckInfo},
+    program::{
+        self,
+        run::{CheckError, CheckInfo},
+    },
 };
 
 use super::Config;
@@ -16,13 +19,27 @@ impl Config {
     /// `run_command: fn` runs a command with arguments.
     /// Args: (cmd, args) where cmd is a string and args is an Iterable over strings
     /// `RunCommandError` holds the error if the command can't be executed
+    /// returns (int/(), string, string) on success (status code, stdout, stderr)
     pub fn with_command_running(self) -> Self {
         self.add_var(
             "run_command".to_string(),
             Data::new(data::function::Function {
                 info: Arc::new(program::run::Info::neverused()),
                 info_check: Arc::new(Mutex::new( CheckInfo::neverused())),
-                out: Arc::new(|a, i| todo!()),
+                out: Arc::new(|a, _i| {
+                    if a.types.iter().all(|t| t.as_any().downcast_ref::<data::tuple::TupleT>().is_some_and(|t| t.0.len() == 2 && t.0[0].is_included_in(&data::string::StringT) && t.0[1].iterable().is_some_and(|t| t.is_included_in(&data::string::StringT)))) {
+                        Ok(Type::newm(vec![
+                            Arc::new(data::tuple::TupleT(vec![
+                                Type::newm(vec![Arc::new(data::int::IntT), Arc::new(data::tuple::TupleT(vec![]))]),
+                                Type::new(data::string::StringT),
+                                Type::new(data::string::StringT),
+                            ])),
+                            Arc::new(RunCommandErrorT)
+                        ]))
+                    } else {
+                        return Err(CheckError(format!("run_command called with invalid arguments (must be (String, Iter<String>))")));
+                    }
+                }),
                 run: Arc::new(|a, _i| {
                     if let Some(cmd) = a.get().as_any().downcast_ref::<data::tuple::Tuple>() {
                         if let (Some(cmd), Some(args)) = (cmd.get(0), cmd.get(1)) {

mers_lib/src/program/configs/with_iters.rs

@@ -18,7 +18,7 @@ impl Config {
     /// `iter: fn` executes a function once for each element of the iterable
     /// `map: fn` maps each value in the iterable to a new one by applying a transformation function
     /// `filter: fn` filters the iterable by removing all elements where the filter function doesn't return true
-    /// `filter_map: fn` combines filter and map
+    /// `filter_map: fn` combines filter and map. requires that the function returns ()/(t).
     /// `enumerate: fn` transforms an iterator over T into one over (Int, T), where Int is the index of the element
     pub fn with_iters(self) -> Self {
         self.add_var(
@@ -49,7 +49,8 @@ impl Config {
                                     }
                                 } else {
                                     return Err(CheckError(format!(
-                                        "for_each called on tuple not containing iterable and function"
+                                        "for_each called on tuple not containing iterable and function: {v} is {}",
+                                        if v.iterable().is_some() { "iterable" } else { "not iterable" },
                                     )));
                                 }
                             } else {

mers_lib/src/program/configs/with_list.rs

@@ -5,7 +5,10 @@ use std::{
 
 use crate::{
     data::{self, Data, MersData, MersType, Type},
-    program::{self, run::CheckInfo},
+    program::{
+        self,
+        run::{CheckError, CheckInfo},
+    },
 };
 
 use super::Config;
@@ -14,9 +17,118 @@ impl Config {
     /// Adds a simple list type
     /// `List` can store a variable number of items
     /// `as_list: fn` turns a tuple into a list
+    /// `push: fn` adds an element to a list
+    /// `pop: fn` removes the last element from a list. returns (element) or ().
+    /// TODO!
+    /// `get_mut: fn` like get, but returns a reference to the object
     pub fn with_list(self) -> Self {
         // TODO: Type with generics
         self.add_type("List".to_string(), Type::new(ListT(Type::empty_tuple())))
+            .add_var(
+                "pop".to_string(),
+                Data::new(data::function::Function {
+                    info: Arc::new(program::run::Info::neverused()),
+                    info_check: Arc::new(Mutex::new(CheckInfo::neverused())),
+                    out: Arc::new(|a, _i| {
+                        if let Some(a) = a.dereference() {
+                            let mut out = Type::empty();
+                            for t in a.types.iter() {
+                                if let Some(t) = t.as_any().downcast_ref::<ListT>() {
+                                    out.add(Arc::new(t.0.clone()));
+                                } else {
+                                    return Err(CheckError(format!(
+                                        "pop: found a reference to {t}, which is not a list"
+                                    )));
+                                }
+                            }
+                            Ok(out)
+                        } else {
+                            return Err(CheckError(format!("pop: not a reference: {a}")));
+                        }
+                    }),
+                    run: Arc::new(|a, _i| {
+                        match a
+                            .get()
+                            .as_any()
+                            .downcast_ref::<data::reference::Reference>()
+                            .unwrap()
+                            .0
+                            .lock()
+                            .unwrap()
+                            .get_mut()
+                            .mut_any()
+                            .downcast_mut::<List>()
+                            .unwrap()
+                            .0
+                            .pop()
+                        {
+                            Some(data) => Data::one_tuple(data),
+                            None => Data::empty_tuple(),
+                        }
+                    }),
+                }),
+            )
+            .add_var(
+                "push".to_string(),
+                Data::new(data::function::Function {
+                    info: Arc::new(program::run::Info::neverused()),
+                    info_check: Arc::new(Mutex::new(CheckInfo::neverused())),
+                    out: Arc::new(|a, _i| {
+                        for t in a.types.iter() {
+                            if let Some(t) = t.as_any().downcast_ref::<data::tuple::TupleT>() {
+                                if t.0.len() != 2 {
+                                    return Err(CheckError(format!(
+                                        "push: tuple must have length 2"
+                                    )));
+                                }
+                                let a = &t.0[0];
+                                let new = &t.0[1];
+                                if let Some(a) = a.dereference() {
+                                    for t in a.types.iter() {
+                                        if let Some(t) = t.as_any().downcast_ref::<ListT>() {
+                                            if !new.is_included_in(&t.0) {
+                                                return Err(CheckError(format!(
+                                            "push: found a reference to {t}, which is a list which can't contain elements of type {new}"
+                                        )));
+                                            }
+                                        } else {
+                                            return Err(CheckError(format!(
+                                            "push: found a reference to {t}, which is not a list"
+                                        )));
+                                        }
+                                    }
+                                } else {
+                                    return Err(CheckError(format!(
+                                        "push: first element in tuple not a reference: {a}"
+                                    )));
+                                }
+                            } else {
+                                return Err(CheckError(format!("push: not a tuple: {t}")));
+                            }
+                        }
+                        Ok(Type::empty_tuple())
+                    }),
+                    run: Arc::new(|a, _i| {
+                        let tuple = a.get();
+                        let tuple = tuple.as_any().downcast_ref::<data::tuple::Tuple>().unwrap();
+                        tuple.0[0]
+                            .get()
+                            .as_any()
+                            .downcast_ref::<data::reference::Reference>()
+                            .unwrap()
+                            .0
+                            .lock()
+                            .unwrap()
+                            .get_mut()
+                            .mut_any()
+                            .downcast_mut::<List>()
+                            .unwrap()
+                            .0
+                            .push(tuple.0[1].clone());
+                            Data::empty_tuple()
+                    }),
+                }),
+            )
             .add_var(
                 "as_list".to_string(),
                 Data::new(data::function::Function {

mers_lib/src/program/configs/with_math.rs

@@ -1,7 +1,7 @@
 use std::sync::{Arc, Mutex};
 
 use crate::{
-    data::{self, Data, Type},
+    data::{self, Data, MersType, Type},
     program::{
         self,
         run::{CheckError, CheckInfo},
@@ -12,13 +12,135 @@ use super::Config;
 
 impl Config {
     /// `sum: fn` returns the sum of all the numbers in the tuple
+    /// `diff: fn` returns b - a
+    /// `product: fn` returns the product of all the numbers in the tuple
+    /// `signum: fn` returns 1 for positive numbers, -1 for negative ones and 0 for 0 (always returns an Int, even when input is Float)
+    /// `parse_int: fn` parses a string to an int, returns () on failure
+    /// `parse_float: fn` parses a string to an int, returns () on failure
+    /// TODO!
+    /// `as_float: fn` turns integers into floats. returns floats without changing them.
+    /// `round: fn` rounds the float and returns an int
+    /// `ceil: fn` rounds the float [?] and returns an int
+    /// `floor: fn` rounds the float [?] and returns an int
+    /// `div: fn` returns a / b. Performs integer division if a and b are both integers.
+    /// `modulo: fn` returns a % b
     pub fn with_math(self) -> Self {
-        self.add_var(
+        self.add_var("parse_float".to_string(), Data::new(data::function::Function {
+            info: Arc::new(program::run::Info::neverused()),
+            info_check: Arc::new(Mutex::new(CheckInfo::neverused())),
+            out: Arc::new(|a, _i| {
+                if a.is_included_in(&Type::new(data::string::StringT)) {
+                    Ok(Type::newm(vec![
+                        Arc::new(data::float::FloatT),
+                        Arc::new(data::tuple::TupleT(vec![])),
+                    ]))
+                } else {
+                    Err(CheckError(format!("parse_float called on non-string type")))
+                }
+            }),
+            run: Arc::new(|a, _i| {
+                if let Ok(n) = a.get().as_any().downcast_ref::<data::string::String>().unwrap().0.parse() {
+                    Data::new(data::float::Float(n))
+                } else {
+                    Data::empty_tuple()
+                }
+            })
+        })).add_var("parse_int".to_string(), Data::new(data::function::Function {
+            info: Arc::new(program::run::Info::neverused()),
+            info_check: Arc::new(Mutex::new(CheckInfo::neverused())),
+            out: Arc::new(|a, _i| {
+                if a.is_included_in(&Type::new(data::string::StringT)) {
+                    Ok(Type::newm(vec![
+                        Arc::new(data::int::IntT),
+                        Arc::new(data::tuple::TupleT(vec![])),
+                    ]))
+                } else {
+                    Err(CheckError(format!("parse_float called on non-string type")))
+                }
+            }),
+            run: Arc::new(|a, _i| {
+                if let Ok(n) = a.get().as_any().downcast_ref::<data::string::String>().unwrap().0.parse() {
+                    Data::new(data::int::Int(n))
+                } else {
+                    Data::empty_tuple()
+                }
+            })
+        })).add_var("signum".to_string(), Data::new(data::function::Function {
+            info: Arc::new(program::run::Info::neverused()),
+            info_check: Arc::new(Mutex::new(CheckInfo::neverused())),
+            out: Arc::new(|a, _i| {
+                if a.is_included_in(&Type::newm(vec![Arc::new(data::int::IntT), Arc::new(data::float::FloatT)])) {
+                    Ok(Type::new(data::int::IntT))
+                } else {
+                    Err(CheckError(format!("signum called on non-number type")))
+                }
+            }),
+            run: Arc::new(|a, _i| {
+                Data::new(data::int::Int(if let Some(n) = a.get().as_any().downcast_ref::<data::int::Int>() {
+                    n.0.signum()
+                } else
+                if let Some(n) = a.get().as_any().downcast_ref::<data::float::Float>() {
+                    if n.0 > 0.0 {
+                        1
+                    } else if n.0 < 0.0 {
+                        -1
+                    } else { 0
+                    }
+                } else { unreachable!("called signum on non-number type")}))
+            })
+        }))
+            .add_var("diff".to_string(), Data::new(data::function::Function {
+                info: Arc::new(program::run::Info::neverused()),
+                info_check: Arc::new(Mutex::new(CheckInfo::neverused())),
+                out: Arc::new(|a, _i| {
+                    let mut float = false;
+                    for t in &a.types {
+                        if let Some(t) = t.as_any().downcast_ref::<data::tuple::TupleT>() {
+                            if t.0.len() != 2 {
+                                return Err(CheckError(format!("Called diff with a tuple where len != 2")));
+                            }
+                            for (t, side) in [(&t.0[0], "left"), (&t.0[1], "right")] {
+                                for t in t.types.iter() {
+                                    if t.as_any().is::<data::float::FloatT>() {
+                                        float = true;
+                                    } else if !t.as_any().is::<data::int::IntT>() {
+                                        return Err(CheckError(format!("Called diff, but the {side} side of the tuple had type {t}, which isn't Int/Float.")));
+                                    }
+                                }
+                            }
+                        } else {
+                            return Err(CheckError(format!("Called diff on a non-tuple")));
+                        }
+                    }
+                    Ok(if a.types.is_empty() {
+                        Type::empty()
+                    } else if float {
+                        Type::new(data::float::FloatT)
+                    } else {
+                        Type::new(data::int::IntT)
+                    })
+                }),
+                run: Arc::new(|a, _i| if let Some(t) = a.get().as_any().downcast_ref::<data::tuple::Tuple>() {
+                    let left = t.0[0].get();
+                    let right = t.0[1].get();
+                    let (left, right) = (left.as_any(), right.as_any());
+                    match (left.downcast_ref::<data::int::Int>(), left.downcast_ref::<data::float::Float>(),
+                        right.downcast_ref::<data::int::Int>(), right.downcast_ref::<data::float::Float>()
+                    ) {
+                        (Some(data::int::Int(l)), None, Some(data::int::Int(r)), None) => Data::new(data::int::Int(r - l)),
+                        (Some(data::int::Int(l)), None, None, Some(data::float::Float(r))) => Data::new(data::float::Float(r - *l as f64)),
+                        (None, Some(data::float::Float(l)), Some(data::int::Int(r)), None) => Data::new(data::float::Float(*r as f64 - l)),
+                        (None, Some(data::float::Float(l)), None, Some(data::float::Float(r))) => Data::new(data::float::Float(r - l)),
+                        _ => unreachable!(),
+                    }
+                } else { unreachable!() }),
+            }))
+            .add_var(
             "sum".to_string(),
             Data::new(data::function::Function {
                 info: Arc::new(program::run::Info::neverused()),
                 info_check: Arc::new(Mutex::new(CheckInfo::neverused())),
-                out: Arc::new(|a, i| {
+                out: Arc::new(|a, _i| {
                     let mut ints = false;
                     let mut floats = false;
                     for a in &a.types {
@@ -74,5 +196,66 @@ impl Config {
                 }),
             }),
         )
+            .add_var(
+            "product".to_string(),
+            Data::new(data::function::Function {
+                info: Arc::new(program::run::Info::neverused()),
+                info_check: Arc::new(Mutex::new(CheckInfo::neverused())),
+                out: Arc::new(|a, _i| {
+                    let mut ints = false;
+                    let mut floats = false;
+                    for a in &a.types {
+                        if let Some(i) = a.iterable() {
+                            if i.types
+                                .iter()
+                                .all(|t| t.as_any().downcast_ref::<data::int::IntT>().is_some())
+                            {
+                                ints = true;
+                            } else if i.types.iter().all(|t| {
+                                t.as_any().downcast_ref::<data::int::IntT>().is_some()
+                                    || t.as_any().downcast_ref::<data::float::FloatT>().is_some()
+                            }) {
+                                floats = true;
+                            } else {
+                                return Err(CheckError(format!("cannot get product of iterator over type {i} because it contains types that aren't int/float")))
+                            }
+                        } else {
+                            return Err(CheckError(format!(
+                                "cannot get product of non-iterable type {a}"
+                            )));
+                        }
+                    }
+                    Ok(match (ints, floats) {
+                        (_, true) => Type::new(data::float::FloatT),
+                        (true, false) => Type::new(data::int::IntT),
+                        (false, false) => Type::empty(),
+                    })
+                }),
+                run: Arc::new(|a, _i| {
+                    if let Some(i) = a.get().iterable() {
+                        let mut prodi = 1;
+                        let mut prodf = 1.0;
+                        let mut usef = false;
+                        for val in i {
+                            if let Some(i) = val.get().as_any().downcast_ref::<data::int::Int>() {
+                                prodi *= i.0;
+                            } else if let Some(i) =
+                                val.get().as_any().downcast_ref::<data::float::Float>()
+                            {
+                                prodf *= i.0;
+                                usef = true;
+                            }
+                        }
+                        if usef {
+                            Data::new(data::float::Float(prodi as f64 + prodf))
+                        } else {
+                            Data::new(data::int::Int(prodi))
+                        }
+                    } else {
+                        unreachable!("product called on non-tuple")
+                    }
+                }),
+            }),
+        )
     }
 }

mers_lib/src/program/configs/with_multithreading.rs

@@ -12,7 +12,6 @@ use crate::{
 use super::Config;
 
 impl Config {
-    /// `get: fn` is used to retrieve elements from collections
     /// `thread: fn` turns `(func, arg)` into a `Thread`, which will run the function with the argument.
     /// `thread_get_result: fn` returns `()` while the thread is running and `(result)` otherwise.
     pub fn with_multithreading(self) -> Self {

mers_lib/src/program/configs/with_string.rs

@@ -0,0 +1,132 @@
+use std::sync::{Arc, Mutex};
+
+use crate::{
+    data::{self, Data, MersType, Type},
+    program::run::{CheckError, CheckInfo, Info},
+};
+
+use super::Config;
+
+impl Config {
+    /// `substring: fn` extracts part of a string. usage: (str, start).substring or (str, start, end).substring. start and end may be negative, in which case they become str.len - n: (str, 0, -1) shortens the string by 1.
+    /// `index_of: fn` finds the index of a pattern in a string
+    /// `index_of_rev: fn` finds the last index of a pattern in a string
+    /// `to_string: fn` turns any argument into a (more or less useful) string representation
+    /// `concat: fn` concatenates all arguments given to it. arg must be an enumerable
+    pub fn with_string(self) -> Self {
+        self.add_var("concat".to_string(), Data::new(data::function::Function {
+            info: Arc::new(Info::neverused()),
+            info_check: Arc::new(Mutex::new(CheckInfo::neverused())),
+            out: Arc::new(|a, _i| if a.iterable().is_some() {
+                Ok(Type::new(data::string::StringT))
+            } else {
+                Err(CheckError(format!("concat called on non-iterable type {a}")))
+            }),
+            run: Arc::new(|a, _i| Data::new(data::string::String(a.get().iterable().unwrap().map(|v| v.get().to_string()).collect()))),
+        })).add_var("to_string".to_string(), Data::new(data::function::Function {
+            info: Arc::new(Info::neverused()),
+            info_check: Arc::new(Mutex::new(CheckInfo::neverused())),
+            out: Arc::new(|_a, _i| Ok(Type::new(data::string::StringT))),
+            run: Arc::new(|a, _i| Data::new(data::string::String(a.get().to_string()))),
+        })).add_var("index_of".to_string(), Data::new(data::function::Function {
+            info: Arc::new(Info::neverused()),
+            info_check: Arc::new(Mutex::new(CheckInfo::neverused())),
+            out: Arc::new(|a, _i| if a.is_included_in(&data::tuple::TupleT(vec![Type::new(data::string::StringT), Type::new(data::string::StringT)])) {
+                Ok(Type::newm(vec![
+                    Arc::new(data::tuple::TupleT(vec![])),
+                    Arc::new(data::int::IntT),
+                ]))
+            } else {
+                Err(CheckError(format!("wrong args for index_of: must be (string, string)")))
+            }),
+            run: Arc::new(|a, _i| index_of(a, false)),
+        })).add_var("index_of_rev".to_string(), Data::new(data::function::Function {
+            info: Arc::new(Info::neverused()),
+            info_check: Arc::new(Mutex::new(CheckInfo::neverused())),
+            out: Arc::new(|a, _i| if a.is_included_in(&data::tuple::TupleT(vec![Type::new(data::string::StringT), Type::new(data::string::StringT)])) {
+                Ok(Type::newm(vec![
+                    Arc::new(data::tuple::TupleT(vec![])),
+                    Arc::new(data::int::IntT),
+                ]))
+            } else {
+                Err(CheckError(format!("wrong args for index_of: must be (string, string)")))
+            }),
+            run: Arc::new(|a, _i| index_of(a, true)),
+        })).add_var("substring".to_string(), Data::new(data::function::Function {
+            info: Arc::new(Info::neverused()),
+            info_check: Arc::new(Mutex::new(CheckInfo::neverused())),
+            out: Arc::new(|a, _i| {
+                for t in a.types.iter() {
+                    if let Some(t) = t.as_any().downcast_ref::<data::tuple::TupleT>() {
+                        if t.0.len() != 2 && t.0.len() != 3 {
+                            return Err(CheckError(format!("cannot call substring with tuple argument of len != 3")));
+                        }
+                        if !t.0[0].is_included_in(&data::string::StringT) {
+                            return Err(CheckError(format!("cannot call substring with tuple argument that isn't (*string*, int, int)")));
+                        }
+                        if !t.0[1].is_included_in(&data::int::IntT) {
+                            return Err(CheckError(format!("cannot call substring with tuple argument that isn't (string, *int*, int)")));
+                        }
+                        if t.0.len() > 2 && !t.0[2].is_included_in(&data::int::IntT) {
+                            return Err(CheckError(format!("cannot call substring with tuple argument that isn't (string, int, *int*)")));
+                        }
+                    } else {
+                        return Err(CheckError(format!("cannot call substring with non-tuple argument.")));
+                    }
+                }
+                Ok(if a.types.is_empty() {
+                    Type::empty()
+                } else {
+                    Type::new(data::string::StringT)
+                })
+            }),
+            run: Arc::new(|a, _i| {
+                let tuple = a.get();
+                let tuple = tuple.as_any().downcast_ref::<data::tuple::Tuple>().expect("called substring with non-tuple arg");
+                let (s, start, end) = (&tuple.0[0], &tuple.0[1], tuple.0.get(2));
+                let s = s.get();
+                let s = &s.as_any().downcast_ref::<data::string::String>().unwrap().0;
+                let start = start.get();
+                let start = start.as_any().downcast_ref::<data::int::Int>().unwrap().0;
+                let start = if start < 0 { s.len().saturating_sub(start.abs() as usize) } else { start as usize };
+                let end = end
+                    .map(|end| end.get())
+                    .map(|end| end.as_any().downcast_ref::<data::int::Int>().unwrap().0)
+                    .map(|i| if i < 0 { s.len().saturating_sub(i.abs() as usize) } else { i as usize })
+                    .unwrap_or(usize::MAX);
+                let end = end.min(s.len());
+                if end < start {
+                    return Data::new(data::string::String(String::new()));
+                }
+                Data::new(data::string::String(s[start..end].to_owned()))
+
+            }),
+        }))
+    }
+}
+
+fn index_of(a: Data, rev: bool) -> Data {
+    let a = a.get();
+    let a = a
+        .as_any()
+        .downcast_ref::<data::tuple::Tuple>()
+        .expect("index_of called on non-tuple");
+    let src = a.0[0].get();
+    let src = &src
+        .as_any()
+        .downcast_ref::<data::string::String>()
+        .unwrap()
+        .0;
+    let pat = a.0[1].get();
+    let pat = &pat
+        .as_any()
+        .downcast_ref::<data::string::String>()
+        .unwrap()
+        .0;
+    let i = if rev { src.rfind(pat) } else { src.find(pat) };
+    if let Some(i) = i {
+        Data::new(data::int::Int(i as _))
+    } else {
+        Data::empty_tuple()
+    }
+}

mers_lib/src/program/run/assign_to.rs

@@ -1,5 +1,5 @@
 use crate::{
-    data::{self, Type},
+    data::{self, Data, MersType, Type},
     parsing::SourcePos,
 };
 
@@ -26,13 +26,24 @@ impl MersStatement for AssignTo {
         }
         let source = self.source.check(info, None)?;
         let target = self.target.check(info, Some(&source))?;
-        Ok(source)
+        if !self.is_init {
+            if let Some(t) = target.dereference() {
+                if !source.is_included_in(&t) {
+                    return Err(CheckError(format!(
+                        "can't assign {source} to {target} because it isn't included in {t}!"
+                    )));
+                }
+            } else {
+                return Err(CheckError(format!("can't assign to non-reference!")));
+            }
+        }
+        Ok(Type::empty_tuple())
     }
     fn run_custom(&self, info: &mut super::Info) -> crate::data::Data {
         let source = self.source.run(info);
         let target = self.target.run(info);
         data::defs::assign(&source, &target);
-        target
+        Data::empty_tuple()
     }
     fn has_scope(&self) -> bool {
         false

mers_lib/src/program/run/variable.rs

@@ -32,13 +32,14 @@ impl MersStatement for Variable {
                 .expect("variable's is_init was true, but check_custom's assign was None? How?")
                 .clone();
         }
-        Ok(if self.is_ref {
+        let val = if self.is_ref {
             Type::new(data::reference::ReferenceT(
                 info.scopes[self.var.0].vars[self.var.1].clone(),
             ))
         } else {
             info.scopes[self.var.0].vars[self.var.1].clone()
-        })
+        };
+        Ok(val)
     }
     fn run_custom(&self, info: &mut super::Info) -> Data {
         if self.is_init {