diff --git a/src/eval.rs b/src/eval.rs
index e596ab1..80f3033 100644
--- a/src/eval.rs
+++ b/src/eval.rs
@@ -1,14 +1,14 @@
 use chrono::NaiveDate;
 
 use crate::files::arguments::{Range, RangeDate};
-use crate::files::Files;
+use crate::files::{FileSource, Files};
 
-use self::command::CommandState;
+use self::command::{CommandState, EvalCommand};
 pub use self::date::Dates;
 use self::delta::Delta;
 use self::entry::Entries;
 pub use self::entry::{Entry, EntryKind, EntryMode};
-pub use self::error::{Error, Result, SourceInfo};
+pub use self::error::Error;
 pub use self::range::DateRange;
 
 mod command;
@@ -20,11 +20,14 @@ mod range;
 mod util;
 
 impl Files {
-    pub fn eval(&self, mode: EntryMode, range: DateRange) -> Result<Vec<Entry>> {
+    pub fn eval(&self, mode: EntryMode, range: DateRange) -> Result<Vec<Entry>, Error<FileSource>> {
         let mut entries = Entries::new(mode, range);
         for command in self.commands() {
-            for entry in CommandState::new(command, range).eval()?.entries() {
-                entries.add(entry);
+            let source = command.source;
+            if let Some(command) = EvalCommand::new(command.command) {
+                for entry in CommandState::new(command, source, range).eval()?.entries() {
+                    entries.add(entry);
+                }
             }
         }
         Ok(entries.entries())
@@ -32,7 +35,7 @@ impl Files {
 }
 
 impl Range {
-    pub fn eval(&self, index: usize, today: NaiveDate) -> Result<DateRange> {
+    pub fn eval<S: Copy>(&self, index: S, today: NaiveDate) -> Result<DateRange, Error<S>> {
         let mut start = match self.start {
             RangeDate::Date(d) => d,
             RangeDate::Today => today,
diff --git a/src/eval/command.rs b/src/eval/command.rs
index b0ec4a5..e50e580 100644
--- a/src/eval/command.rs
+++ b/src/eval/command.rs
@@ -6,18 +6,69 @@ use crate::files::commands::{
     self, BirthdaySpec, Command, Done, DoneDate, DoneKind, Note, Spec, Statement, Task,
 };
 use crate::files::primitives::{Span, Spanned, Time};
-use crate::files::SourcedCommand;
+use crate::files::{FileSource, Source};
 
 use super::date::Dates;
 use super::delta::Delta;
-use super::{DateRange, Entry, EntryKind, Error, Result};
+use super::{DateRange, Entry, EntryKind, Error};
 
 mod birthday;
 mod date;
 mod formula;
 
+/// A command that can be evaluated.
+pub enum EvalCommand<'a> {
+    Task(&'a Task),
+    Note(&'a Note),
+}
+
+impl<'a> EvalCommand<'a> {
+    pub fn new(command: &'a Command) -> Option<Self> {
+        match command {
+            Command::Task(task) => Some(Self::Task(task)),
+            Command::Note(note) => Some(Self::Note(note)),
+            _ => None,
+        }
+    }
+
+    fn statements(&self) -> &[Statement] {
+        match self {
+            Self::Task(task) => &task.statements,
+            Self::Note(note) => &note.statements,
+        }
+    }
+
+    fn kind(&self) -> EntryKind {
+        match self {
+            Self::Task(_) => EntryKind::Task,
+            Self::Note(_) => EntryKind::Note,
+        }
+    }
+
+    /// Last root date mentioned in any `DONE`.
+    fn last_done_root(&self) -> Option<NaiveDate> {
+        match self {
+            Self::Task(task) => task
+                .done
+                .iter()
+                .filter_map(|done| done.date.map(DoneDate::root))
+                .max(),
+            Self::Note(_) => None,
+        }
+    }
+
+    /// Last completion date mentioned in any `DONE`.
+    fn last_done_completion(&self) -> Option<NaiveDate> {
+        match self {
+            Self::Task(task) => task.done.iter().map(|done| done.done_at).max(),
+            Self::Note(_) => None,
+        }
+    }
+}
+
 pub struct CommandState<'a> {
-    command: SourcedCommand<'a>,
+    command: EvalCommand<'a>,
+    source: Source,
     range: DateRange,
 
     from: Option<NaiveDate>,
@@ -29,7 +80,7 @@ pub struct CommandState<'a> {
 }
 
 impl<'a> CommandState<'a> {
-    pub fn new(command: SourcedCommand<'a>, mut range: DateRange) -> Self {
+    pub fn new(command: EvalCommand<'a>, source: Source, mut range: DateRange) -> Self {
         // If we don't calculate entries for the source of the move command, it
         // fails even though the user did nothing wrong. Also, move commands (or
         // chains thereof) may move an initially out-of-range entry into range.
@@ -37,15 +88,16 @@ impl<'a> CommandState<'a> {
         // To fix this, we just expand the range to contain all move command
         // sources. This is a quick fix, but until it becomes a performance
         // issue (if ever), it's probably fine.
-        for statement in command.command.statements() {
+        for statement in command.statements() {
             if let Statement::Move { from, .. } = statement {
                 range = range.containing(*from)
             }
         }
 
         Self {
-            range,
             command,
+            source,
+            range,
             from: None,
             until: None,
             remind: None,
@@ -54,10 +106,10 @@ impl<'a> CommandState<'a> {
         }
     }
 
-    pub fn eval(mut self) -> Result<Self> {
-        match self.command.command {
-            Command::Task(task) => self.eval_task(task)?,
-            Command::Note(note) => self.eval_note(note)?,
+    pub fn eval(mut self) -> Result<Self, Error<FileSource>> {
+        match self.command {
+            EvalCommand::Task(task) => self.eval_task(task)?,
+            EvalCommand::Note(note) => self.eval_note(note)?,
         }
         Ok(self)
     }
@@ -71,13 +123,6 @@ impl<'a> CommandState<'a> {
 
     // Helper functions
 
-    fn kind(&self) -> EntryKind {
-        match self.command.command {
-            Command::Task(_) => EntryKind::Task,
-            Command::Note(_) => EntryKind::Note,
-        }
-    }
-
     fn range_with_remind(&self) -> DateRange {
         match &self.remind {
             None => self.range,
@@ -85,26 +130,6 @@ impl<'a> CommandState<'a> {
         }
     }
 
-    /// Last root date mentioned in any `DONE`.
-    fn last_done_root(&self) -> Option<NaiveDate> {
-        match self.command.command {
-            Command::Task(task) => task
-                .done
-                .iter()
-                .filter_map(|done| done.date.map(DoneDate::root))
-                .max(),
-            Command::Note(_) => None,
-        }
-    }
-
-    /// Last completion date mentioned in any `DONE`.
-    fn last_done_completion(&self) -> Option<NaiveDate> {
-        match self.command.command {
-            Command::Task(task) => task.done.iter().map(|done| done.done_at).max(),
-            Command::Note(_) => None,
-        }
-    }
-
     fn limit_from_until(&self, range: DateRange) -> Option<DateRange> {
         let range_from = range.from();
         let from = self
@@ -125,9 +150,13 @@ impl<'a> CommandState<'a> {
         }
     }
 
-    fn entry_with_remind(&self, kind: EntryKind, dates: Option<Dates>) -> Result<Entry> {
+    fn entry_with_remind(
+        &self,
+        kind: EntryKind,
+        dates: Option<Dates>,
+    ) -> Result<Entry, Error<FileSource>> {
         let remind = if let (Some(dates), Some(delta)) = (dates, &self.remind) {
-            let index = self.command.source.file();
+            let index = self.source.file();
             let start = dates.sorted().root();
             let remind = delta.value.apply_date(index, dates.sorted().root())?;
             if remind >= start {
@@ -143,7 +172,7 @@ impl<'a> CommandState<'a> {
             None
         };
 
-        Ok(Entry::new(self.command.source, kind, dates, remind))
+        Ok(Entry::new(self.source, kind, dates, remind))
     }
 
     /// Add an entry, respecting [`Self::from`] and [`Self::until`]. Does not
@@ -185,13 +214,13 @@ impl<'a> CommandState<'a> {
             .any(|s| matches!(s, Statement::Date(_) | Statement::BDate(_)))
     }
 
-    fn eval_task(&mut self, task: &Task) -> Result<()> {
+    fn eval_task(&mut self, task: &Task) -> Result<(), Error<FileSource>> {
         if Self::has_date_stmt(&task.statements) {
             for statement in &task.statements {
                 self.eval_statement(statement)?;
             }
         } else if task.done.is_empty() {
-            self.add(self.entry_with_remind(self.kind(), None)?);
+            self.add(self.entry_with_remind(self.command.kind(), None)?);
         }
 
         for done in &task.done {
@@ -201,19 +230,19 @@ impl<'a> CommandState<'a> {
         Ok(())
     }
 
-    fn eval_note(&mut self, note: &Note) -> Result<()> {
+    fn eval_note(&mut self, note: &Note) -> Result<(), Error<FileSource>> {
         if Self::has_date_stmt(&note.statements) {
             for statement in &note.statements {
                 self.eval_statement(statement)?;
             }
         } else {
-            self.add(self.entry_with_remind(self.kind(), None)?);
+            self.add(self.entry_with_remind(self.command.kind(), None)?);
         }
 
         Ok(())
     }
 
-    fn eval_statement(&mut self, statement: &Statement) -> Result<()> {
+    fn eval_statement(&mut self, statement: &Statement) -> Result<(), Error<FileSource>> {
         match statement {
             Statement::Date(spec) => self.eval_date(spec)?,
             Statement::BDate(spec) => self.eval_bdate(spec)?,
@@ -231,7 +260,7 @@ impl<'a> CommandState<'a> {
         Ok(())
     }
 
-    fn eval_date(&mut self, spec: &Spec) -> Result<()> {
+    fn eval_date(&mut self, spec: &Spec) -> Result<(), Error<FileSource>> {
         match spec {
             Spec::Date(spec) => self.eval_date_spec(spec.into()),
             Spec::Weekday(spec) => self.eval_formula_spec(spec.into()),
@@ -239,7 +268,7 @@ impl<'a> CommandState<'a> {
         }
     }
 
-    fn eval_bdate(&mut self, spec: &BirthdaySpec) -> Result<()> {
+    fn eval_bdate(&mut self, spec: &BirthdaySpec) -> Result<(), Error<FileSource>> {
         self.eval_birthday_spec(spec)
     }
 
@@ -254,7 +283,7 @@ impl<'a> CommandState<'a> {
         from: NaiveDate,
         to: Option<NaiveDate>,
         to_time: Option<Spanned<Time>>,
-    ) -> Result<()> {
+    ) -> Result<(), Error<FileSource>> {
         if let Some(mut entry) = self.dated.remove(&from) {
             let mut dates = entry.dates.expect("comes from self.dated");
 
@@ -268,7 +297,7 @@ impl<'a> CommandState<'a> {
                     delta = delta + Duration::minutes(root.minutes_to(to_time.value));
                 } else {
                     return Err(Error::TimedMoveWithoutTime {
-                        index: self.command.source.file(),
+                        index: self.source.file(),
                         span: to_time.span,
                     });
                 }
@@ -281,7 +310,7 @@ impl<'a> CommandState<'a> {
             Ok(())
         } else {
             Err(Error::MoveWithoutSource {
-                index: self.command.source.file(),
+                index: self.source.file(),
                 span,
             })
         }
@@ -295,7 +324,7 @@ impl<'a> CommandState<'a> {
         }
     }
 
-    fn eval_done(&mut self, done: &Done) -> Result<()> {
+    fn eval_done(&mut self, done: &Done) -> Result<(), Error<FileSource>> {
         let kind = match done.kind {
             DoneKind::Done => EntryKind::TaskDone(done.done_at),
             DoneKind::Canceled => EntryKind::TaskCanceled(done.done_at),
diff --git a/src/eval/command/birthday.rs b/src/eval/command/birthday.rs
index b10d83f..cec1d2e 100644
--- a/src/eval/command/birthday.rs
+++ b/src/eval/command/birthday.rs
@@ -1,14 +1,15 @@
 use chrono::{Datelike, NaiveDate};
 
 use crate::files::commands::BirthdaySpec;
+use crate::files::FileSource;
 
 use super::super::command::CommandState;
 use super::super::date::Dates;
-use super::super::error::Result;
+use super::super::error::Error;
 use super::super::EntryKind;
 
 impl<'a> CommandState<'a> {
-    pub fn eval_birthday_spec(&mut self, spec: &BirthdaySpec) -> Result<()> {
+    pub fn eval_birthday_spec(&mut self, spec: &BirthdaySpec) -> Result<(), Error<FileSource>> {
         let range = match self.limit_from_until(self.range_with_remind()) {
             Some(range) => range,
             None => return Ok(()),
diff --git a/src/eval/command/date.rs b/src/eval/command/date.rs
index 8ef5ff6..f7ddacb 100644
--- a/src/eval/command/date.rs
+++ b/src/eval/command/date.rs
@@ -1,12 +1,14 @@
 use chrono::NaiveDate;
 
-use crate::files::commands::{self, Command};
+use crate::files::commands;
 use crate::files::primitives::{Spanned, Time};
+use crate::files::FileSource;
 
 use super::super::command::CommandState;
 use super::super::date::Dates;
 use super::super::delta::{Delta, DeltaStep};
-use super::super::{DateRange, Error, Result};
+use super::super::{DateRange, Error};
+use super::EvalCommand;
 
 pub struct DateSpec {
     pub start: NaiveDate,
@@ -72,14 +74,16 @@ impl DateSpec {
     /// `start` date itself should be skipped (and thus not result in an entry).
     /// This may be necessary if [`Self::start_at_done`] is set.
     fn start_and_range(&self, s: &CommandState<'_>) -> Option<(NaiveDate, bool, DateRange)> {
-        let (start, skip, range) = match s.command.command {
-            Command::Task(_) => {
+        let (start, skip, range) = match s.command {
+            EvalCommand::Task(_) => {
                 let (start, skip) = s
+                    .command
                     .last_done_completion()
                     .map(|start| (start, true))
                     .filter(|_| self.start_at_done)
                     .unwrap_or((self.start, false));
                 let range_from = s
+                    .command
                     .last_done_root()
                     .map(|date| date.succ())
                     .unwrap_or(self.start);
@@ -90,7 +94,7 @@ impl DateSpec {
                     .with_from(range_from)?;
                 (start, skip, range)
             }
-            Command::Note(_) => {
+            EvalCommand::Note(_) => {
                 let start = self.start;
                 let range = s
                     .range_with_remind()
@@ -103,7 +107,11 @@ impl DateSpec {
         Some((start, skip, range))
     }
 
-    fn step(index: usize, from: NaiveDate, repeat: &Spanned<Delta>) -> Result<NaiveDate> {
+    fn step(
+        index: FileSource,
+        from: NaiveDate,
+        repeat: &Spanned<Delta>,
+    ) -> Result<NaiveDate, Error<FileSource>> {
         let to = repeat.value.apply_date(index, from)?;
         if to > from {
             Ok(to)
@@ -117,7 +125,7 @@ impl DateSpec {
         }
     }
 
-    fn dates(&self, index: usize, start: NaiveDate) -> Result<Dates> {
+    fn dates(&self, index: FileSource, start: NaiveDate) -> Result<Dates, Error<FileSource>> {
         let root = self.start_delta.apply_date(index, start)?;
         Ok(if let Some(root_time) = self.start_time {
             let (other, other_time) = self.end_delta.apply_date_time(index, root, root_time)?;
@@ -130,8 +138,8 @@ impl DateSpec {
 }
 
 impl<'a> CommandState<'a> {
-    pub fn eval_date_spec(&mut self, spec: DateSpec) -> Result<()> {
-        let index = self.command.source.file();
+    pub fn eval_date_spec(&mut self, spec: DateSpec) -> Result<(), Error<FileSource>> {
+        let index = self.source.file();
         if let Some(repeat) = &spec.repeat {
             if let Some((mut start, skip, range)) = spec.start_and_range(self) {
                 if skip {
@@ -142,13 +150,13 @@ impl<'a> CommandState<'a> {
                 }
                 while start <= range.until() {
                     let dates = spec.dates(index, start)?;
-                    self.add(self.entry_with_remind(self.kind(), Some(dates))?);
+                    self.add(self.entry_with_remind(self.command.kind(), Some(dates))?);
                     start = DateSpec::step(index, start, repeat)?;
                 }
             }
         } else {
             let dates = spec.dates(index, spec.start)?;
-            self.add(self.entry_with_remind(self.kind(), Some(dates))?);
+            self.add(self.entry_with_remind(self.command.kind(), Some(dates))?);
         }
         Ok(())
     }
diff --git a/src/eval/command/formula.rs b/src/eval/command/formula.rs
index 5ecc6a2..e733937 100644
--- a/src/eval/command/formula.rs
+++ b/src/eval/command/formula.rs
@@ -1,12 +1,14 @@
 use chrono::{Datelike, Duration, NaiveDate};
 
-use crate::files::commands::{self, Command};
+use crate::files::commands;
 use crate::files::primitives::{Span, Spanned, Time, Weekday};
+use crate::files::FileSource;
 
 use super::super::command::CommandState;
 use super::super::date::Dates;
 use super::super::delta::{Delta, DeltaStep};
-use super::super::{util, DateRange, Error, Result};
+use super::super::{util, DateRange, Error};
+use super::EvalCommand;
 
 fn b2i(b: bool) -> i64 {
     if b {
@@ -47,7 +49,7 @@ pub enum Var {
 }
 
 impl Var {
-    fn eval(self, index: usize, date: NaiveDate) -> Result<i64> {
+    fn eval<S>(self, index: S, date: NaiveDate) -> Result<i64, Error<S>> {
         Ok(match self {
             Var::JulianDay => date.num_days_from_ce().into(),
             Var::Year => date.year().into(),
@@ -202,7 +204,7 @@ impl From<Weekday> for Expr {
 }
 
 impl Expr {
-    fn eval(&self, index: usize, date: NaiveDate) -> Result<i64> {
+    fn eval<S: Copy>(&self, index: S, date: NaiveDate) -> Result<i64, Error<S>> {
         Ok(match self {
             Expr::Lit(l) => *l,
             Expr::Var(v) => v.eval(index, date)?,
@@ -328,12 +330,12 @@ impl FormulaSpec {
             .expand_by(&self.end_delta)
             .move_by(&self.start_delta);
 
-        if let Command::Task(_) = s.command.command {
-            if let Some(last_done_root) = s.last_done_root() {
+        if let EvalCommand::Task(_) = s.command {
+            if let Some(last_done_root) = s.command.last_done_root() {
                 range = range.with_from(last_done_root.succ())?;
             } else if let Some(from) = s.from {
                 range = range.with_from(from)?;
-            } else if matches!(s.command.command, Command::Task(_)) {
+            } else if matches!(s.command, EvalCommand::Task(_)) {
                 // We have no idea if we missed any tasks since the user hasn't
                 // specified a `FROM`, so we just just look back one year. Any
                 // task older than a year is probably not important anyways...
@@ -344,7 +346,7 @@ impl FormulaSpec {
         s.limit_from_until(range)
     }
 
-    fn dates(&self, index: usize, start: NaiveDate) -> Result<Dates> {
+    fn dates(&self, index: FileSource, start: NaiveDate) -> Result<Dates, Error<FileSource>> {
         let root = self.start_delta.apply_date(index, start)?;
         Ok(if let Some(root_time) = self.start_time {
             let (other, other_time) = self.end_delta.apply_date_time(index, root, root_time)?;
@@ -355,19 +357,19 @@ impl FormulaSpec {
         })
     }
 
-    fn eval(&self, index: usize, date: NaiveDate) -> Result<bool> {
+    fn eval(&self, index: FileSource, date: NaiveDate) -> Result<bool, Error<FileSource>> {
         Ok(i2b(self.start.eval(index, date)?))
     }
 }
 
 impl<'a> CommandState<'a> {
-    pub fn eval_formula_spec(&mut self, spec: FormulaSpec) -> Result<()> {
+    pub fn eval_formula_spec(&mut self, spec: FormulaSpec) -> Result<(), Error<FileSource>> {
         if let Some(range) = spec.range(self) {
-            let index = self.command.source.file();
+            let index = self.source.file();
             for day in range.days() {
                 if spec.eval(index, day)? {
                     let dates = spec.dates(index, day)?;
-                    self.add(self.entry_with_remind(self.kind(), Some(dates))?);
+                    self.add(self.entry_with_remind(self.command.kind(), Some(dates))?);
                 }
             }
         }
@@ -386,7 +388,7 @@ mod tests {
     use super::{Expr, Var};
 
     fn expr(expr: &Expr, date: NaiveDate, target: i64) {
-        if let Ok(result) = expr.eval(0, date) {
+        if let Ok(result) = expr.eval((), date) {
             assert_eq!(result, target);
         } else {
             panic!("formula produced error for day {}", date);
@@ -400,7 +402,7 @@ mod tests {
         for delta in -1000..1000 {
             let d1 = NaiveDate::from_ymd(2021, 12, 19);
             let d2 = d1 + Duration::days(delta);
-            assert_eq!(e.eval(0, d2).unwrap() - e.eval(0, d1).unwrap(), delta);
+            assert_eq!(e.eval((), d2).unwrap() - e.eval((), d1).unwrap(), delta);
         }
     }
 
diff --git a/src/eval/delta.rs b/src/eval/delta.rs
index dcc1706..0872d7b 100644
--- a/src/eval/delta.rs
+++ b/src/eval/delta.rs
@@ -5,7 +5,7 @@ use chrono::{Datelike, Duration, NaiveDate};
 use crate::files::commands;
 use crate::files::primitives::{Span, Spanned, Time, Weekday};
 
-use super::{util, Error, Result};
+use super::{util, Error};
 
 /// Like [`commands::DeltaStep`] but includes a new constructor,
 /// [`DeltaStep::Time`].
@@ -142,16 +142,16 @@ impl From<&commands::Delta> for Delta {
     }
 }
 
-struct DeltaEval {
-    index: usize,
+struct DeltaEval<I> {
+    index: I,
     start: NaiveDate,
     start_time: Option<Time>,
     curr: NaiveDate,
     curr_time: Option<Time>,
 }
 
-impl DeltaEval {
-    fn new(index: usize, start: NaiveDate, start_time: Option<Time>) -> Self {
+impl<S: Copy> DeltaEval<S> {
+    fn new(index: S, start: NaiveDate, start_time: Option<Time>) -> Self {
         Self {
             index,
             start,
@@ -161,7 +161,7 @@ impl DeltaEval {
         }
     }
 
-    fn err_step(&self, span: Span) -> Error {
+    fn err_step(&self, span: Span) -> Error<S> {
         Error::DeltaInvalidStep {
             index: self.index,
             span,
@@ -172,7 +172,7 @@ impl DeltaEval {
         }
     }
 
-    fn err_time(&self, span: Span) -> Error {
+    fn err_time(&self, span: Span) -> Error<S> {
         Error::DeltaNoTime {
             index: self.index,
             span,
@@ -181,7 +181,7 @@ impl DeltaEval {
         }
     }
 
-    fn apply(&mut self, step: &Spanned<DeltaStep>) -> Result<()> {
+    fn apply(&mut self, step: &Spanned<DeltaStep>) -> Result<(), Error<S>> {
         match step.value {
             DeltaStep::Year(n) => self.step_year(step.span, n)?,
             DeltaStep::Month(n) => self.step_month(step.span, n)?,
@@ -196,7 +196,7 @@ impl DeltaEval {
         Ok(())
     }
 
-    fn step_year(&mut self, span: Span, amount: i32) -> Result<()> {
+    fn step_year(&mut self, span: Span, amount: i32) -> Result<(), Error<S>> {
         let year = self.curr.year() + amount;
         match NaiveDate::from_ymd_opt(year, self.curr.month(), self.curr.day()) {
             None => Err(self.err_step(span)),
@@ -207,7 +207,7 @@ impl DeltaEval {
         }
     }
 
-    fn step_month(&mut self, span: Span, amount: i32) -> Result<()> {
+    fn step_month(&mut self, span: Span, amount: i32) -> Result<(), Error<S>> {
         let (year, month) = util::add_months(self.curr.year(), self.curr.month(), amount);
         match NaiveDate::from_ymd_opt(year, month, self.curr.day()) {
             None => Err(self.err_step(span)),
@@ -218,7 +218,7 @@ impl DeltaEval {
         }
     }
 
-    fn step_month_reverse(&mut self, span: Span, amount: i32) -> Result<()> {
+    fn step_month_reverse(&mut self, span: Span, amount: i32) -> Result<(), Error<S>> {
         // Calculate offset from the last day of the month
         let month_length = util::month_length(self.curr.year(), self.curr.month()) as i32;
         let end_offset = self.curr.day() as i32 - month_length;
@@ -252,7 +252,7 @@ impl DeltaEval {
         self.curr += delta;
     }
 
-    fn step_hour(&mut self, span: Span, amount: i32) -> Result<()> {
+    fn step_hour(&mut self, span: Span, amount: i32) -> Result<(), Error<S>> {
         let time = match self.curr_time {
             Some(time) => time,
             None => return Err(self.err_time(span)),
@@ -264,7 +264,7 @@ impl DeltaEval {
         Ok(())
     }
 
-    fn step_minute(&mut self, span: Span, amount: i32) -> Result<()> {
+    fn step_minute(&mut self, span: Span, amount: i32) -> Result<(), Error<S>> {
         let time = match self.curr_time {
             Some(time) => time,
             None => return Err(self.err_time(span)),
@@ -290,7 +290,7 @@ impl DeltaEval {
         }
     }
 
-    fn step_time(&mut self, span: Span, time: Time) -> Result<()> {
+    fn step_time(&mut self, span: Span, time: Time) -> Result<(), Error<S>> {
         let curr_time = match self.curr_time {
             Some(time) => time,
             None => return Err(self.err_time(span)),
@@ -313,11 +313,11 @@ impl Delta {
         self.steps.iter().map(|step| step.value.upper_bound()).sum()
     }
 
-    fn apply(
+    fn apply<S: Copy>(
         &self,
-        index: usize,
+        index: S,
         start: (NaiveDate, Option<Time>),
-    ) -> Result<(NaiveDate, Option<Time>)> {
+    ) -> Result<(NaiveDate, Option<Time>), Error<S>> {
         let mut eval = DeltaEval::new(index, start.0, start.1);
         for step in &self.steps {
             eval.apply(step)?;
@@ -325,16 +325,16 @@ impl Delta {
         Ok((eval.curr, eval.curr_time))
     }
 
-    pub fn apply_date(&self, index: usize, date: NaiveDate) -> Result<NaiveDate> {
+    pub fn apply_date<S: Copy>(&self, index: S, date: NaiveDate) -> Result<NaiveDate, Error<S>> {
         Ok(self.apply(index, (date, None))?.0)
     }
 
-    pub fn apply_date_time(
+    pub fn apply_date_time<S: Copy>(
         &self,
-        index: usize,
+        index: S,
         date: NaiveDate,
         time: Time,
-    ) -> Result<(NaiveDate, Time)> {
+    ) -> Result<(NaiveDate, Time), Error<S>> {
         let (date, time) = self.apply(index, (date, Some(time)))?;
         Ok((date, time.expect("time was not preserved")))
     }
@@ -346,7 +346,7 @@ mod tests {
 
     use crate::files::primitives::{Span, Spanned, Time};
 
-    use super::super::Result;
+    use super::super::Error;
     use super::{Delta, DeltaStep as Step};
 
     const SPAN: Span = Span { start: 12, end: 34 };
@@ -357,8 +357,8 @@ mod tests {
         }
     }
 
-    fn apply_d(step: Step, from: (i32, u32, u32)) -> Result<NaiveDate> {
-        delta(step).apply_date(0, NaiveDate::from_ymd(from.0, from.1, from.2))
+    fn apply_d(step: Step, from: (i32, u32, u32)) -> Result<NaiveDate, Error<()>> {
+        delta(step).apply_date((), NaiveDate::from_ymd(from.0, from.1, from.2))
     }
 
     fn test_d(step: Step, from: (i32, u32, u32), expected: (i32, u32, u32)) {
@@ -368,9 +368,12 @@ mod tests {
         );
     }
 
-    fn apply_dt(step: Step, from: (i32, u32, u32, u32, u32)) -> Result<(NaiveDate, Time)> {
+    fn apply_dt(
+        step: Step,
+        from: (i32, u32, u32, u32, u32),
+    ) -> Result<(NaiveDate, Time), Error<()>> {
         delta(step).apply_date_time(
-            0,
+            (),
             NaiveDate::from_ymd(from.0, from.1, from.2),
             Time::new(from.3, from.4),
         )
diff --git a/src/eval/error.rs b/src/eval/error.rs
index 5219f7f..16062b9 100644
--- a/src/eval/error.rs
+++ b/src/eval/error.rs
@@ -1,15 +1,15 @@
-use std::result;
-
 use chrono::NaiveDate;
+use codespan_reporting::diagnostic::{Diagnostic, Label};
 
 use crate::files::primitives::{Span, Time};
+use crate::files::{FileSource, Files};
 
 #[derive(Debug, thiserror::Error)]
-pub enum Error {
+pub enum Error<S> {
     /// A delta step resulted in an invalid date.
     #[error("delta step resulted in invalid date")]
     DeltaInvalidStep {
-        index: usize,
+        index: S,
         span: Span,
         start: NaiveDate,
         start_time: Option<Time>,
@@ -19,7 +19,7 @@ pub enum Error {
     /// A time-based delta step was applied to a date without time.
     #[error("time-based delta step applied to date without time")]
     DeltaNoTime {
-        index: usize,
+        index: S,
         span: Span,
         start: NaiveDate,
         prev: NaiveDate,
@@ -29,7 +29,7 @@ pub enum Error {
     /// in time (`to < from`).
     #[error("repeat delta did not move forwards")]
     RepeatDidNotMoveForwards {
-        index: usize,
+        index: S,
         span: Span,
         from: NaiveDate,
         to: NaiveDate,
@@ -39,7 +39,7 @@ pub enum Error {
     /// moved forwards in time (`from < to`).
     #[error("remind delta did not move backwards")]
     RemindDidNotMoveBackwards {
-        index: usize,
+        index: S,
         span: Span,
         from: NaiveDate,
         to: NaiveDate,
@@ -47,55 +47,36 @@ pub enum Error {
     /// A `MOVE a TO b` statement was executed, but there was no entry at the
     /// date `a`.
     #[error("tried to move nonexisting entry")]
-    MoveWithoutSource { index: usize, span: Span },
+    MoveWithoutSource { index: S, span: Span },
     /// A `MOVE a TO b` statement was executed where `b` contains a time but `a`
     /// doesn't was executed.
     #[error("tried to move un-timed entry to new time")]
-    TimedMoveWithoutTime { index: usize, span: Span },
+    TimedMoveWithoutTime { index: S, span: Span },
     /// A division by zero has occurred.
     #[error("tried to divide by zero")]
     DivByZero {
-        index: usize,
+        index: S,
         span: Span,
         date: NaiveDate,
     },
     /// A modulo operation by zero has occurred.
     #[error("tried to modulo by zero")]
     ModByZero {
-        index: usize,
+        index: S,
         span: Span,
         date: NaiveDate,
     },
     /// Easter calculation failed.
     #[error("easter calculation failed")]
     Easter {
-        index: usize,
+        index: S,
         span: Span,
         date: NaiveDate,
         msg: &'static str,
     },
 }
 
-pub struct SourceInfo<'a> {
-    pub name: Option<String>,
-    pub content: &'a str,
-}
-
-impl Error {
-    fn print_at<'a>(sources: &[SourceInfo<'a>], index: &usize, span: &Span, message: String) {
-        use pest::error as pe;
-
-        let source = sources.get(*index).expect("index is valid");
-        let span = pest::Span::new(source.content, span.start, span.end).expect("span is valid");
-        let variant = pe::ErrorVariant::<()>::CustomError { message };
-        let mut error = pe::Error::new_from_span(variant, span);
-        if let Some(name) = &source.name {
-            error = error.with_path(name);
-        }
-
-        eprintln!("{}", error);
-    }
-
+impl Error<FileSource> {
     fn fmt_date_time(date: NaiveDate, time: Option<Time>) -> String {
         match time {
             None => format!("{}", date),
@@ -103,8 +84,8 @@ impl Error {
         }
     }
 
-    pub fn print<'a>(&self, sources: &[SourceInfo<'a>]) {
-        match self {
+    pub fn print(&self, files: &Files) {
+        let diagnostic = match self {
             Error::DeltaInvalidStep {
                 index,
                 span,
@@ -113,95 +94,91 @@ impl Error {
                 prev,
                 prev_time,
             } => {
-                let msg = format!(
-                    "Delta step resulted in invalid date\
-                    \nInitial start: {}\
-                    \nPrevious step: {}",
-                    Self::fmt_date_time(*start, *start_time),
-                    Self::fmt_date_time(*prev, *prev_time),
-                );
-                Self::print_at(sources, index, span, msg);
+                let start_str = Self::fmt_date_time(*start, *start_time);
+                let prev_str = Self::fmt_date_time(*prev, *prev_time);
+                Diagnostic::error()
+                    .with_message("Delta step resulted in invalid date")
+                    .with_labels(vec![
+                        Label::primary(files.cs_id(*index), span).with_message("At this step")
+                    ])
+                    .with_notes(vec![
+                        format!("Date before applying delta: {}", start_str),
+                        format!("Date before applying this step: {}", prev_str),
+                    ])
             }
             Error::DeltaNoTime {
                 index,
                 span,
                 start,
                 prev,
-            } => {
-                let msg = format!(
-                    "Time-based delta step applied to date without time\
-                    \nInitial start: {}\
-                    \nPrevious step: {}",
-                    start, prev
-                );
-                Self::print_at(sources, index, span, msg);
-            }
+            } => Diagnostic::error()
+                .with_message("Time-based delta step applied to date without time")
+                .with_labels(vec![
+                    Label::primary(files.cs_id(*index), span).with_message("At this step")
+                ])
+                .with_notes(vec![
+                    format!("Date before applying delta: {}", start),
+                    format!("Date before applying this step: {}", prev),
+                ]),
             Error::RepeatDidNotMoveForwards {
                 index,
                 span,
                 from,
                 to,
-            } => {
-                let msg = format!(
-                    "Repeat delta did not move forwards\
-                    \nMoved from {} to {}",
-                    from, to
-                );
-                Self::print_at(sources, index, span, msg);
-            }
+            } => Diagnostic::error()
+                .with_message("Repeat delta did not move forwards")
+                .with_labels(vec![
+                    Label::primary(files.cs_id(*index), span).with_message("This delta")
+                ])
+                .with_notes(vec![format!("Moved from {} to {}", from, to)]),
             Error::RemindDidNotMoveBackwards {
                 index,
                 span,
                 from,
                 to,
-            } => {
-                let msg = format!(
-                    "Remind delta did not move backwards\
-                    \nMoved from {} to {}",
-                    from, to
-                );
-                Self::print_at(sources, index, span, msg);
-            }
-            Error::MoveWithoutSource { index, span } => {
-                let msg = "Tried to move nonexisting entry".to_string();
-                Self::print_at(sources, index, span, msg);
-            }
-            Error::TimedMoveWithoutTime { index, span } => {
-                let msg = "Tried to move un-timed entry to new time".to_string();
-                Self::print_at(sources, index, span, msg);
-            }
-            Error::DivByZero { index, span, date } => {
-                let msg = format!(
-                    "Tried to divide by zero\
-                    \nAt date: {}",
-                    date
-                );
-                Self::print_at(sources, index, span, msg);
-            }
-            Error::ModByZero { index, span, date } => {
-                let msg = format!(
-                    "Tried to modulo by zero\
-                    \nAt date: {}",
-                    date
-                );
-                Self::print_at(sources, index, span, msg);
-            }
+            } => Diagnostic::error()
+                .with_message("Remind delta did not move backwards")
+                .with_labels(vec![
+                    Label::primary(files.cs_id(*index), span).with_message("This delta")
+                ])
+                .with_notes(vec![format!("Moved from {} to {}", from, to)]),
+            Error::MoveWithoutSource { index, span } => Diagnostic::error()
+                .with_message("Tried to move nonexistent entry")
+                .with_labels(vec![
+                    Label::primary(files.cs_id(*index), span).with_message("Here")
+                ]),
+            Error::TimedMoveWithoutTime { index, span } => Diagnostic::error()
+                .with_message("Tried to move un-timed entry to new time")
+                .with_labels(vec![
+                    Label::primary(files.cs_id(*index), span).with_message("Here")
+                ]),
+            Error::DivByZero { index, span, date } => Diagnostic::error()
+                .with_message("Tried to divide by zero")
+                .with_labels(vec![
+                    Label::primary(files.cs_id(*index), span).with_message("This expression")
+                ])
+                .with_notes(vec![format!("At date: {}", date)]),
+            Error::ModByZero { index, span, date } => Diagnostic::error()
+                .with_message("Tried to modulo by zero")
+                .with_labels(vec![
+                    Label::primary(files.cs_id(*index), span).with_message("This expression")
+                ])
+                .with_notes(vec![format!("At date: {}", date)]),
             Error::Easter {
                 index,
                 span,
                 date,
                 msg,
-            } => {
-                let msg = format!(
-                    "Failed to calculate easter\
-                    \nAt date: {}\
-                    \nReason: {}",
-                    date, msg
-                );
-                Self::print_at(sources, index, span, msg);
-            }
-        }
+            } => Diagnostic::error()
+                .with_message("Failed to calculate easter")
+                .with_labels(vec![
+                    Label::primary(files.cs_id(*index), span).with_message("This expression")
+                ])
+                .with_notes(vec![
+                    format!("At date: {}", date),
+                    format!("Reason: {}", msg),
+                ]),
+        };
+        files.eprint_diagnostic(&diagnostic);
     }
 }
-
-pub type Result<T> = result::Result<T, Error>;
diff --git a/src/main.rs b/src/main.rs
index 40770a6..9053d12 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -4,7 +4,7 @@
 #![warn(clippy::use_self)]
 
 mod cli;
-// mod eval;
+mod eval;
 mod files;
 
 fn main() {