diff --git a/simple.ed b/simple.ed
index df490fdcf..788b78dd3 100644
--- a/simple.ed
+++ b/simple.ed
@@ -8,17 +8,17 @@ fn test(x: Hello) {
 }
 
 fn works(x: i64) -> i64 {
-    let z = 0;
+    let z = 0i64;
     if 2 == x {
-        z = x * 2;
+        z = x * 2i64;
     } else {
-        z = x * 3;
+        z = x * 3i64;
     }
     return z;
 }
 
 fn main() -> i64 {
-    let y = 2;
+    let y = 2i64;
     let z = y;
     return works(z);
 }
diff --git a/src/ast/mod.rs b/src/ast/mod.rs
index 14b67573e..8668853ad 100644
--- a/src/ast/mod.rs
+++ b/src/ast/mod.rs
@@ -53,8 +53,8 @@ pub enum LiteralValue {
     String(String),
     Integer {
         value: String,
-        bits: Option<u32>,
-        signed: Option<bool>,
+        bits: u32,
+        signed: bool,
     },
     Boolean(bool),
 }
diff --git a/src/check.rs b/src/check.rs
index cba22f397..eddeff9fa 100644
--- a/src/check.rs
+++ b/src/check.rs
@@ -1,11 +1,14 @@
 use crate::{
     ast::{self, Statement},
     codegen::ProgramData,
+    lexer::LexicalError,
+    tokens::Token,
 };
 use annotate_snippets::{
     display_list::{DisplayList, FormatOptions},
     snippet::{Annotation, AnnotationType, Slice, Snippet, SourceAnnotation},
 };
+use lalrpop_util::ParseError;
 
 #[derive(Debug)]
 pub enum Check<'a> {
@@ -82,3 +85,65 @@ pub fn check<'a>(data: &'a ProgramData, ast: &ast::Program) -> Vec<Check<'a>> {
     }
     errors
 }
+
+pub fn print_error(source: &str, err: ParseError<usize, Token, LexicalError>) {
+    match err {
+        ParseError::InvalidToken { location } => {
+            let snippet = Snippet {
+                title: None,
+                footer: vec![],
+                slices: vec![Slice {
+                    source,
+                    line_start: 1,
+                    fold: true,
+                    origin: None,
+
+                    annotations: vec![SourceAnnotation {
+                        label: "invalid token",
+                        annotation_type: AnnotationType::Error,
+                        range: (location, location),
+                    }],
+                }],
+                opt: FormatOptions {
+                    color: true,
+                    ..Default::default()
+                },
+            };
+            let dl = DisplayList::from(snippet);
+            println!("{dl}");
+        }
+        ParseError::UnrecognizedEof { location, expected } => todo!(),
+        ParseError::UnrecognizedToken { token, expected } => todo!(),
+        ParseError::ExtraToken { token } => todo!(),
+        ParseError::User { error } => match error {
+            LexicalError::InvalidToken(err, range) => {
+                let title = format!("invalid token (lexical error): {:?}", err);
+                let snippet = Snippet {
+                    title: Some(Annotation {
+                        id: None,
+                        label: Some(&title),
+                        annotation_type: AnnotationType::Error,
+                    }),
+                    footer: vec![],
+                    slices: vec![Slice {
+                        source: dbg!(source),
+                        line_start: 1,
+                        fold: false,
+                        origin: None,
+                        annotations: vec![SourceAnnotation {
+                            label: "invalid token (lexical error)",
+                            annotation_type: AnnotationType::Error,
+                            range: dbg!((range.start, range.end)),
+                        }],
+                    }],
+                    opt: FormatOptions {
+                        color: true,
+                        ..Default::default()
+                    },
+                };
+                let dl = DisplayList::from(snippet);
+                println!("{dl}");
+            }
+        },
+    };
+}
diff --git a/src/codegen.rs b/src/codegen.rs
index 7133a4c2e..73bbe567e 100644
--- a/src/codegen.rs
+++ b/src/codegen.rs
@@ -552,8 +552,8 @@ impl<'ctx> CodeGen<'ctx> {
                 bits,
                 signed,
             } => {
-                let bits = bits.unwrap_or(32);
-                let signed = signed.unwrap_or(true);
+                let bits = *bits;
+                let signed = *signed;
                 (
                     self.context
                         .custom_width_int_type(bits)
diff --git a/src/grammar.lalrpop b/src/grammar.lalrpop
index adeb1e360..78bfc0ec7 100644
--- a/src/grammar.lalrpop
+++ b/src/grammar.lalrpop
@@ -24,6 +24,8 @@ extern {
       "return" => Token::KeywordReturn,
       "fn" => Token::KeywordFn,
       "ptr" => Token::KeywordPtr,
+      "_" => Token::KeywordUnderscore,
+
       "(" => Token::LeftParen,
       ")" => Token::RightParen,
       "{" => Token::LeftBracket,
@@ -151,10 +153,52 @@ Term: Box<ast::Expression> = {
     "(" <Term> ")"
 };
 
-Number: ast::LiteralValue = <n:"int literal"> => ast::LiteralValue::Integer {
-    value: n,
-    bits: None,
-    signed: None
+Number: ast::LiteralValue = {
+    <n:"int literal"> "_"? "i8" => ast::LiteralValue::Integer {
+        value: n,
+        bits: 8,
+        signed: true,
+    },
+    <n:"int literal"> "_"? "i16" => ast::LiteralValue::Integer {
+        value: n,
+        bits: 16,
+        signed: true,
+    },
+    <n:"int literal"> "_"? "i32" => ast::LiteralValue::Integer {
+        value: n,
+        bits: 32,
+        signed: true,
+    },
+    <n:"int literal"> "_"? "i64" => ast::LiteralValue::Integer {
+        value: n,
+        bits: 64,
+        signed: true,
+    },
+    <n:"int literal"> "_"? "u8" => ast::LiteralValue::Integer {
+        value: n,
+        bits: 8,
+        signed: false,
+    },
+    <n:"int literal"> "_"? "u16" => ast::LiteralValue::Integer {
+        value: n,
+        bits: 16,
+        signed: false,
+    },
+    <n:"int literal"> "_"? "u32" => ast::LiteralValue::Integer {
+        value: n,
+        bits: 32,
+        signed: false,
+    },
+    <n:"int literal"> "_"? "u64" => ast::LiteralValue::Integer {
+        value: n,
+        bits: 64,
+        signed: false,
+    },
+    <n:"int literal"> => ast::LiteralValue::Integer {
+        value: n,
+        bits: 32,
+        signed: true,
+    },
 };
 
 StringLit: ast::LiteralValue = <n:"string literal"> => ast::LiteralValue::String(n[1..(n.len()-1)].to_string());
diff --git a/src/lexer.rs b/src/lexer.rs
index 2c6a5d61a..8d4eda6f8 100644
--- a/src/lexer.rs
+++ b/src/lexer.rs
@@ -2,19 +2,21 @@ use std::{fmt::Display, ops::Range};
 
 use logos::{Logos, SpannedIter};
 
-use crate::tokens::Token;
+use crate::tokens::{LexingError, Token};
 
 pub type Spanned<Tok, Loc, Error> = Result<(Loc, Tok, Loc), Error>;
 
 #[derive(Debug, Clone)]
 pub enum LexicalError {
-    InvalidToken(Range<usize>),
+    InvalidToken(LexingError, Range<usize>),
 }
 
 impl Display for LexicalError {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {
-            LexicalError::InvalidToken(span) => write!(f, "lexical error at: {:?}", span),
+            LexicalError::InvalidToken(err, span) => {
+                write!(f, "lexical error at ({:?}): {:?}", err, span)
+            }
         }
     }
 }
@@ -39,7 +41,7 @@ impl<'input> Iterator for Lexer<'input> {
     fn next(&mut self) -> Option<Self::Item> {
         self.token_stream.next().map(|(token, span)| match token {
             Ok(token) => Ok((span.start, token, span.end)),
-            Err(()) => Err(LexicalError::InvalidToken(span)),
+            Err(err) => Err(LexicalError::InvalidToken(err, span)),
         })
     }
 }
diff --git a/src/main.rs b/src/main.rs
index 2eb62cd93..47403110b 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,5 +1,6 @@
 #![allow(clippy::too_many_arguments)]
 
+use check::print_error;
 use clap::{Parser, Subcommand};
 use codegen::ProgramData;
 use color_eyre::Result;
@@ -101,7 +102,7 @@ fn main() -> Result<()> {
             let lexer = Lexer::new(code.as_str());
             let parser = grammar::ProgramParser::new();
             let mut ast = parser.parse(lexer)?;
-            type_analysis::type_inference(&mut ast);
+            type_analysis::type_inference2(&mut ast);
             let program = ProgramData::new(&input, &code);
             check_program(&program, &ast);
         }
@@ -109,9 +110,15 @@ fn main() -> Result<()> {
             let code = fs::read_to_string(input)?;
             let lexer = Lexer::new(code.as_str());
             let parser = grammar::ProgramParser::new();
-            let mut ast = parser.parse(lexer)?;
-            type_analysis::type_inference2(&mut ast);
-            println!("{ast:#?}");
+            match parser.parse(lexer) {
+                Ok(mut ast) => {
+                    type_analysis::type_inference2(&mut ast);
+                    println!("{ast:#?}");
+                }
+                Err(e) => {
+                    print_error(&code, e);
+                }
+            }
         }
         Commands::Compile {
             input,
@@ -123,7 +130,7 @@ fn main() -> Result<()> {
             let lexer = Lexer::new(code.as_str());
             let parser = grammar::ProgramParser::new();
             let mut ast: Program = parser.parse(lexer)?;
-            type_analysis::type_inference(&mut ast);
+            type_analysis::type_inference2(&mut ast);
 
             let program = ProgramData::new(&input, &code);
 
diff --git a/src/tokens.rs b/src/tokens.rs
index 21cc791b8..3f22260f3 100644
--- a/src/tokens.rs
+++ b/src/tokens.rs
@@ -1,9 +1,30 @@
 use logos::Logos;
-use std::fmt;
+use std::{convert::Infallible, fmt};
+
+//  https://github.com/maciejhirsz/logos/issues/133
+
+#[derive(Debug, PartialEq, Clone, Default)]
+pub enum LexingError {
+    NumberParseError,
+    #[default]
+    Other,
+}
+
+impl From<std::num::ParseIntError> for LexingError {
+    fn from(_: std::num::ParseIntError) -> Self {
+        LexingError::NumberParseError
+    }
+}
+
+impl From<Infallible> for LexingError {
+    fn from(_: Infallible) -> Self {
+        LexingError::Other
+    }
+}
 
 // todo: https://github.com/maciejhirsz/logos/issues/133#issuecomment-619444615
 #[derive(Logos, Debug, PartialEq, Clone)]
-#[logos(skip r"[ \t\n\f]+", skip r"#.*\n?")]
+#[logos(error = LexingError, skip r"[ \t\n\f]+", skip r"#.*\n?")]
 pub enum Token {
     #[token("let")]
     KeywordLet,
@@ -21,14 +42,16 @@ pub enum Token {
     KeywordIf,
     #[token("else")]
     KeywordElse,
+    #[token("_")]
+    KeywordUnderscore,
 
-    #[regex(r"_?\p{XID_Start}\p{XID_Continue}*", |lex| lex.slice().parse().ok())]
+    #[regex(r"_?\p{XID_Start}\p{XID_Continue}*", |lex| lex.slice().to_string())]
     Identifier(String),
-    #[regex(r"\d+", |lex| lex.slice().parse().ok())]
+    #[regex(r"\d+", |lex| lex.slice().to_string())]
     Integer(String),
     #[regex(r#""(?:[^"]|\\")*""#, |lex| lex.slice().to_string())]
     String(String),
-    #[regex(r"(true|false)", |lex| lex.slice().parse().ok())]
+    #[regex(r"(true|false)", |lex| lex.slice().parse::<bool>().unwrap())]
     Boolean(bool),
 
     #[token("bool")]
diff --git a/src/type_analysis.rs b/src/type_analysis.rs
index 07849ff64..a5517cc05 100644
--- a/src/type_analysis.rs
+++ b/src/type_analysis.rs
@@ -1,7 +1,5 @@
 use std::collections::{HashMap, HashSet};
 
-use tracing::{info, warn};
-
 use crate::ast::{self, Expression, Function, Statement, TypeExp};
 
 #[derive(Debug, Clone, Default)]
@@ -10,7 +8,18 @@ struct Storage {
     functions: HashMap<String, Function>,
 }
 
+/*
+To briefly summarize the union-find algorithm, given the set of all types in a proof,
+it allows one to group them together into equivalence classes by means of a union procedure and to
+ pick a representative for each such class using a find procedure. Emphasizing the word procedure in
+ the sense of side effect, we're clearly leaving the realm of logic in order to prepare an effective algorithm.
+  The representative of a u n i o n ( a , b ) {\mathtt {union}}(a,b) is determined such that, if both a and b are
+  type variables then the representative is arbitrarily one of them, but while uniting a variable and a term, the
+  term becomes the representative. Assuming an implementation of union-find at hand, one can formulate the unification of two monotypes as follows:
+ */
+
 // this works, but need to find a way to store the found info + handle literal integer types (or not?)
+// maybe use scope ids
 pub fn type_inference2(ast: &mut ast::Program) {
     let mut storage = Storage::default();
 
@@ -166,16 +175,10 @@ fn type_inference_expression(
                     value: _,
                     bits,
                     signed,
-                } => {
-                    if bits.is_some() && signed.is_some() {
-                        Some(TypeExp::Integer {
-                            bits: bits.unwrap(),
-                            signed: signed.unwrap(),
-                        })
-                    } else {
-                        None
-                    }
-                }
+                } => Some(TypeExp::Integer {
+                    bits: *bits,
+                    signed: *signed,
+                }),
                 ast::LiteralValue::Boolean(_) => Some(TypeExp::Boolean),
             }
         }
@@ -230,318 +233,3 @@ fn type_inference_expression(
         },
     }
 }
-
-pub fn type_inference(ast: &mut ast::Program) {
-    let mut struct_cache: HashMap<String, HashMap<String, TypeExp>> = HashMap::new();
-    for statement in ast.statements.iter_mut() {
-        if let Statement::Struct(st) = statement {
-            let fields = st
-                .fields
-                .iter()
-                .map(|x| (x.ident.clone(), x.type_exp.clone()))
-                .collect();
-            struct_cache.insert(st.name.clone(), fields);
-        }
-    }
-
-    let mut fn_cache: HashMap<String, Function> = HashMap::new();
-    for statement in ast.statements.iter_mut() {
-        if let Statement::Function(function) = statement {
-            fn_cache.insert(function.name.clone(), function.clone());
-        }
-    }
-
-    for statement in ast.statements.iter_mut() {
-        if let Statement::Function(function) = statement {
-            let ret_type = function.return_type.clone();
-            let mut var_cache: HashMap<String, TypeExp> = HashMap::new();
-
-            for arg in &function.params {
-                var_cache.insert(arg.ident.clone(), arg.type_exp.clone());
-            }
-
-            if let Some(ret_type) = &ret_type {
-                let ret_type_exp = fn_return_type(function);
-
-                if let Some(exp) = ret_type_exp {
-                    set_expression_type(exp, ret_type, &mut var_cache);
-                }
-            }
-
-            update_statements(&mut function.body, &mut var_cache, &fn_cache);
-        }
-    }
-}
-
-fn update_statements(
-    statements: &mut [Statement],
-    var_cache: &mut HashMap<String, TypeExp>,
-    fn_cache: &HashMap<String, Function>,
-) {
-    let mut var_cache = var_cache.clone();
-
-    {
-        let mut let_or_mut: Vec<&mut Statement> = statements
-            .iter_mut()
-            .filter(|x| matches!(x, Statement::Let { .. } | Statement::Mutate { .. }))
-            .collect();
-
-        // process mutate first
-        for st in let_or_mut.iter_mut() {
-            if let Statement::Mutate {
-                name,
-                value,
-                value_type,
-                ..
-            } = st
-            {
-                if let Some(value_type) = value_type {
-                    // todo: check types matches?
-                    var_cache.insert(name.clone(), value_type.clone());
-                    set_expression_type(value, value_type, &mut var_cache);
-                } else {
-                    // evalue the value expr first to find a possible type.
-                    if var_cache.contains_key(name) {
-                        *value_type = var_cache.get(name).cloned();
-                        let mut env = Some(value_type.clone().unwrap());
-                        set_exp_types_from_cache(value, &mut var_cache, &mut env, fn_cache);
-                    } else {
-                        // no type info?
-                    }
-                }
-            }
-        }
-
-        // we need to process lets with a specified type first.
-        for st in let_or_mut.iter_mut() {
-            if let Statement::Let {
-                name,
-                value,
-                value_type,
-                ..
-            } = st
-            {
-                if let Some(value_type) = value_type {
-                    // todo: check types matches?
-                    var_cache.insert(name.clone(), value_type.clone());
-                    set_expression_type(value, value_type, &mut var_cache);
-                } else {
-                    // evalue the value expr first to find a possible type.
-                    if var_cache.contains_key(name) {
-                        *value_type = var_cache.get(name).cloned();
-                        let mut env = Some(value_type.clone().unwrap());
-                        set_exp_types_from_cache(value, &mut var_cache, &mut env, fn_cache);
-                    } else {
-                        // no type info?
-                    }
-                }
-            }
-        }
-    }
-
-    for st in statements.iter_mut() {
-        match st {
-            Statement::Let {
-                name,
-                value_type,
-                value,
-                ..
-            } => {
-                // infer type if let has no type
-                if value_type.is_none() {
-                    // evalue the value expr first to find a possible type.
-                    let mut env = None;
-                    set_exp_types_from_cache(value, &mut var_cache, &mut env, fn_cache);
-
-                    // try to find if it was set on the cache
-                    if var_cache.contains_key(name) {
-                        *value_type = var_cache.get(name).cloned();
-                        set_expression_type(value, value_type.as_ref().unwrap(), &mut var_cache);
-                    } else {
-                        // what here? no let type, no cache
-                        println!("no cache let found")
-                    }
-                }
-            }
-            Statement::Mutate {
-                name,
-                value_type,
-                value,
-                ..
-            } => {
-                if let Some(value_type) = value_type {
-                    // todo: check types matches?
-                    var_cache.insert(name.clone(), value_type.clone());
-                    set_expression_type(value, value_type, &mut var_cache);
-                } else {
-                    // evalue the value expr first to find a possible type.
-                    if var_cache.contains_key(name) {
-                        *value_type = var_cache.get(name).cloned();
-                        let mut env = Some(value_type.clone().unwrap());
-                        set_exp_types_from_cache(value, &mut var_cache, &mut env, fn_cache);
-                    } else {
-                        // no type info?
-                    }
-                }
-            }
-            Statement::If {
-                condition,
-                body,
-                else_body,
-            } => {
-                let mut env = None;
-                set_exp_types_from_cache(condition, &mut var_cache, &mut env, fn_cache);
-                update_statements(body, &mut var_cache, fn_cache);
-                if let Some(else_body) = else_body {
-                    update_statements(else_body, &mut var_cache, fn_cache);
-                }
-            }
-            Statement::Return(exp) => {
-                if let Some(exp) = exp {
-                    let mut env = None;
-                    set_exp_types_from_cache(exp, &mut var_cache, &mut env, fn_cache);
-                }
-            }
-            Statement::Function(_) => unreachable!(),
-            Statement::Struct(_) => unreachable!(),
-        }
-    }
-}
-
-fn fn_return_type(func: &mut Function) -> Option<&mut Box<Expression>> {
-    for st in func.body.iter_mut() {
-        if let Statement::Return(r) = st {
-            return r.as_mut();
-        }
-    }
-    None
-}
-
-// set variables using the cache
-fn set_exp_types_from_cache(
-    exp: &mut Expression,
-    var_cache: &mut HashMap<String, TypeExp>,
-    env: &mut Option<TypeExp>,
-    fn_cache: &HashMap<String, Function>,
-) {
-    match exp {
-        Expression::Variable { name, value_type } => {
-            let name = name.value.clone();
-            if let Some(value_type) = value_type {
-                // todo: check types matches?
-                var_cache.insert(name, value_type.clone());
-                *env = Some(value_type.clone());
-            } else if var_cache.contains_key(&name) {
-                *value_type = var_cache.get(&name).cloned();
-                if env.is_none() {
-                    *env = value_type.clone();
-                }
-            }
-        }
-        Expression::BinaryOp(lhs, op, rhs) => match op {
-            ast::OpCode::Eq | ast::OpCode::Ne => {
-                set_exp_types_from_cache(lhs, var_cache, env, fn_cache);
-                set_exp_types_from_cache(rhs, var_cache, env, fn_cache);
-                set_exp_types_from_cache(lhs, var_cache, env, fn_cache);
-                *env = Some(TypeExp::Boolean);
-            }
-            _ => {
-                set_exp_types_from_cache(lhs, var_cache, env, fn_cache);
-                set_exp_types_from_cache(rhs, var_cache, env, fn_cache);
-                set_exp_types_from_cache(lhs, var_cache, env, fn_cache); // needed in case 2 == x
-            }
-        },
-        Expression::Literal(lit) => match lit {
-            ast::LiteralValue::String(_) => {
-                warn!("found string, unimplemented")
-            }
-            ast::LiteralValue::Integer { bits, signed, .. } => {
-                if let Some(TypeExp::Integer {
-                    bits: t_bits,
-                    signed: t_signed,
-                }) = env
-                {
-                    *bits = Some(*t_bits);
-                    *signed = Some(*t_signed);
-                }
-            }
-            ast::LiteralValue::Boolean(_) => {
-                warn!("found bool, unimplemented")
-            }
-        },
-        Expression::Call {
-            function,
-            args,
-            value_type,
-        } => {
-            let fn_type = fn_cache.get(function).unwrap().clone();
-            match value_type {
-                Some(value_type) => *env = Some(value_type.clone()),
-                None => {
-                    if env.is_some() {
-                        let env = env.clone();
-                        *value_type = env.clone();
-                    } else {
-                        *value_type = fn_type.return_type.clone();
-                        *env = fn_type.return_type.clone();
-                    }
-                }
-            }
-
-            for (i, arg) in args.iter_mut().enumerate() {
-                let mut env = Some(fn_type.params[i].type_exp.clone());
-                set_exp_types_from_cache(arg, var_cache, &mut env, fn_cache);
-            }
-        }
-    }
-}
-
-fn set_expression_type(
-    exp: &mut Expression,
-    expected_type: &TypeExp,
-    var_cache: &mut HashMap<String, TypeExp>,
-) {
-    match exp {
-        Expression::Variable { name, value_type } => {
-            // if needed?
-            if value_type.is_none() {
-                *value_type = Some(expected_type.clone());
-            }
-            if !var_cache.contains_key(&name.value) {
-                var_cache.insert(name.value.clone(), expected_type.clone());
-            }
-        }
-        Expression::BinaryOp(lhs, op, rhs) => match op {
-            // ast::OpCode::Eq | ast::OpCode::Ne => {}
-            _ => {
-                set_expression_type(lhs, expected_type, var_cache);
-                set_expression_type(rhs, expected_type, var_cache);
-            }
-        },
-        Expression::Literal(lit) => match lit {
-            ast::LiteralValue::String(_) => {
-                warn!("found string, unimplemented")
-            }
-            ast::LiteralValue::Integer { bits, signed, .. } => {
-                if let TypeExp::Integer {
-                    bits: t_bits,
-                    signed: t_signed,
-                } = expected_type
-                {
-                    *bits = Some(*t_bits);
-                    *signed = Some(*t_signed);
-                }
-            }
-            ast::LiteralValue::Boolean(_) => {
-                warn!("found bool, unimplemented")
-            }
-        },
-        Expression::Call {
-            function: _,
-            args: _,
-            value_type,
-        } => {
-            *value_type = Some(expected_type.clone());
-        }
-    }
-}