diff --git a/src/compiler.rs b/src/compiler.rs
index aa00c99..95c660b 100644
--- a/src/compiler.rs
+++ b/src/compiler.rs
@@ -1,8 +1,15 @@
-use std::{collections::HashMap, fmt::Debug, str::FromStr};
+use std::{
+    collections::{BTreeMap, HashMap},
+    fmt::Debug,
+    str::FromStr,
+};
 
 use derive_new::new;
 use derive_wrapper::{AsRef, From};
-use fasteval::{Compiler, Instruction, Slab};
+use fasteval::{Compiler, Evaler, Instruction, Slab};
+use thiserror::Error;
+
+const SAMPLE_RATE: u16 = 48000;
 
 #[derive(From, AsRef)]
 #[cfg_attr(test, derive(Debug))]
@@ -10,16 +17,12 @@ pub struct TokenVec<'a>(pub(crate) Vec<Box<dyn Token + 'a>>);
 
 #[cfg(not(test))]
 pub trait Token {
-    fn apply(&self, context: Context) -> Context {
-        todo!()
-    }
+    fn apply(&self, context: Context) -> Result<Context, CompilerError>;
 }
 
 #[cfg(test)]
 pub trait Token: Debug {
-    fn apply(&self, context: Context) -> Context {
-        todo!()
-    }
+    fn apply(&self, context: Context) -> Result<Context, CompilerError>;
 }
 
 #[cfg(test)]
@@ -33,24 +36,45 @@ impl PartialEq for TokenVec<'_> {
 #[cfg_attr(test, derive(Debug, PartialEq))]
 pub struct Silence;
 
-impl Token for Silence {}
+impl Token for Silence {
+    fn apply(&self, mut context: Context) -> Result<Context, CompilerError> {
+        context.render(None)?;
+        Ok(context)
+    }
+}
 
 #[derive(Clone, Copy)]
 #[cfg_attr(test, derive(Debug, PartialEq))]
 pub struct Marker;
 
-impl Token for Marker {}
+impl Token for Marker {
+    fn apply(&self, mut context: Context) -> Result<Context, CompilerError> {
+        context.result.clear();
+        Ok(context)
+    }
+}
 
 #[derive(Clone, Copy)]
 #[cfg_attr(test, derive(Debug, PartialEq))]
 pub struct Note(pub u8);
 
-impl Token for Note {}
+impl Token for Note {
+    fn apply(&self, mut context: Context) -> Result<Context, CompilerError> {
+        let mut next = context.render(Some(self.0))?;
+        context.result.append(&mut next);
+        Ok(context)
+    }
+}
 
 #[cfg_attr(test, derive(Debug, PartialEq))]
 pub struct VariableChange(pub char, pub Expression);
 
-impl Token for VariableChange {}
+impl Token for VariableChange {
+    fn apply(&self, mut context: Context) -> Result<Context, CompilerError> {
+        *context.get_mut(self.0)? = context.eval(&self.1)?;
+        Ok(context)
+    }
+}
 
 #[cfg_attr(test, derive(Debug, PartialEq))]
 pub struct Loop<'a>(pub LoopCount, pub TokenVec<'a>);
@@ -67,17 +91,29 @@ impl Default for LoopCount {
     }
 }
 
-impl Token for Loop<'_> {}
+impl Token for Loop<'_> {
+    fn apply(&self, context: Context) -> Result<Context, CompilerError> {
+        todo!()
+    }
+}
 
 #[cfg_attr(test, derive(Debug, PartialEq))]
 pub struct Tuplet<'a>(pub TokenVec<'a>);
 
-impl Token for Tuplet<'_> {}
+impl Token for Tuplet<'_> {
+    fn apply(&self, context: Context) -> Result<Context, CompilerError> {
+        todo!()
+    }
+}
 
 #[cfg_attr(test, derive(Debug, PartialEq))]
 pub struct Slope<'a>(pub &'a VariableChange, pub TokenVec<'a>);
 
-impl Token for Slope<'_> {}
+impl Token for Slope<'_> {
+    fn apply(&self, context: Context) -> Result<Context, CompilerError> {
+        todo!()
+    }
+}
 
 #[derive(new)]
 #[cfg_attr(any(debug_assertions, test), derive(Debug))]
@@ -119,11 +155,112 @@ pub struct Context {
     pub slopes: HashMap<char, Expression>,
 }
 
+#[derive(Debug, Error)]
+#[error("variable not found: {0}")]
+pub struct VariableNotFoundError(char);
+
+#[derive(Debug, Error)]
+#[error("expression not found: {0}")]
+pub struct SlopeNotFoundError(char);
+
+#[derive(Debug, Error)]
+pub enum CompilerError {
+    #[error("expression evaluation: {0:?}")]
+    FastEval(#[from] fasteval::Error),
+    #[error("{0}")]
+    VariableNotFound(#[from] VariableNotFoundError),
+    #[error("{0}")]
+    SlopeNotFound(#[from] SlopeNotFoundError),
+}
+
 impl Context {
-    pub fn current_length(&self) -> f64 {
-        todo!()
+    pub fn current_length(&self) -> Result<f64, CompilerError> {
+        self.eval(self.get_slope('l').map_err(CompilerError::from)?)
+            .map_err(Into::into)
     }
-    pub fn render(&self, n: Option<u8>) -> Vec<f64> {
-        todo!()
+
+    pub fn get(&self, name: char) -> Result<&f64, VariableNotFoundError> {
+        self.variables.get(&name).ok_or(VariableNotFoundError(name))
+    }
+
+    pub fn get_mut(&mut self, name: char) -> Result<&mut f64, VariableNotFoundError> {
+        self.variables
+            .get_mut(&name)
+            .ok_or(VariableNotFoundError(name))
+    }
+
+    pub fn get_slope(&self, name: char) -> Result<&Expression, SlopeNotFoundError> {
+        self.slopes.get(&name).ok_or(SlopeNotFoundError(name))
+    }
+
+    fn tick(&mut self) -> Result<(), CompilerError> {
+        *self.get_mut('t')? += 1f64 / SAMPLE_RATE as f64;
+        {
+            let changes = self
+            .slopes
+            .iter()
+            .map(
+                |(v, Expression { instruction, slab })| -> Result<(char, f64), fasteval::Error> {
+                    Ok((
+                        *v,
+                        instruction.eval(
+                            slab,
+                            &mut self
+                                .variables
+                                .iter()
+                                .map(|(c, f)| (c.to_string(), *f))
+                                .collect::<BTreeMap<String, f64>>(),
+                        )?,
+                    ))
+                },
+            )
+            .collect::<Result<Vec<(char, f64)>, fasteval::Error>>()?;
+            for (variable, new_value) in changes {
+                *self.get_mut(variable)? = new_value;
+            }
+        }
+        Ok(())
+    }
+
+    fn namespace_generator(&self) -> BTreeMap<String, f64> {
+        self.variables
+            .iter()
+            .map(|(c, f)| (c.to_string(), *f))
+            .collect()
+    }
+
+    pub fn eval(
+        &self,
+        Expression { instruction, slab }: &Expression,
+    ) -> Result<f64, fasteval::Error> {
+        instruction.eval(&slab, &mut self.namespace_generator())
+    }
+
+    pub fn render(&mut self, n: Option<u8>) -> Result<Vec<f64>, CompilerError> {
+        let curr_t = *self.get('t')?;
+        if let Some(note) = n {
+            let mut result = Vec::new();
+            while (self.current_length()? * SAMPLE_RATE as f64) > *self.get('t')? - curr_t {
+                {
+                    let Expression { instruction, slab } = &self.instrument;
+                    result.push(instruction.eval(&slab, &mut {
+                        let mut map = self
+                            .variables
+                            .iter()
+                            .map(|(c, f)| (format!("{c}"), *f))
+                            .collect::<BTreeMap<String, f64>>();
+                        map.insert('n'.to_string(), note as f64);
+                        map
+                    })?);
+                }
+                self.tick()?;
+            }
+            Ok(result)
+        } else {
+            while (self.current_length()? * SAMPLE_RATE as f64) > *self.get('t')? - curr_t {
+                self.tick()?;
+            }
+            Ok(vec![0.0; (*self.get('t')? - curr_t) as usize])
+        }
     }
 }