2 files changed, 136 insertions, 0 deletions
diff --git a/pest_consume/Cargo.toml b/pest_consume/Cargo.toml
new file mode 100644
index 0000000..b3f1db7
--- /dev/null
+++ b/pest_consume/Cargo.toml
@@ -0,0 +1,13 @@
+[package]
+name = "pest_consume"
+version = "0.1.0"  # remember to update html_root_url
+authors = ["Nadrieril <nadrieril@users.noreply.github.com>"]
+license = "MIT OR Apache-2.0"
+edition = "2018"
+description = "A framework for processing the output of a pest-generated parser"
+readme = "README.md"
+repository = "https://github.com/Nadrieril/dhall-rust"
+
+[dependencies]
+pest = "2.1"
+dhall_proc_macros = { path = "../dhall_proc_macros" }
diff --git a/pest_consume/src/lib.rs b/pest_consume/src/lib.rs
new file mode 100644
index 0000000..1cedc74
--- /dev/null
+++ b/pest_consume/src/lib.rs
@@ -0,0 +1,123 @@
+use pest::error::{Error, ErrorVariant};
+use pest::iterators::Pair;
+use pest::Span;
+
+pub use dhall_proc_macros::{make_parser, parse_children};
+
+/// Carries a pest Pair alongside custom user data.
+#[derive(Debug, Clone)]
+pub struct ParseInput<'input, 'data, Rule, Data>
+where
+    Rule: pest::RuleType,
+{
+    pair: Pair<'input, Rule>,
+    user_data: &'data Data,
+}
+
+impl<'input, 'data, Rule, Data> ParseInput<'input, 'data, Rule, Data>
+where
+    Rule: pest::RuleType,
+{
+    pub fn new(pair: Pair<'input, Rule>, user_data: &'data Data) -> Self {
+        ParseInput { pair, user_data }
+    }
+    /// Create an error that points to the span of the input.
+    pub fn error(&self, message: String) -> Error<Rule> {
+        let message = format!(
+            "{} while matching on:\n{}",
+            message,
+            debug_pair(self.pair.clone())
+        );
+        Error::new_from_span(
+            ErrorVariant::CustomError { message },
+            self.as_span(),
+        )
+    }
+    /// Reconstruct the input with a new pair, passing the user data along.
+    pub fn with_pair(&self, new_pair: Pair<'input, Rule>) -> Self {
+        ParseInput {
+            pair: new_pair,
+            user_data: self.user_data,
+        }
+    }
+    /// If the contained pair has exactly one child, return a new Self containing it.
+    pub fn single_child(&self) -> Option<Self> {
+        let mut children = self.pair.clone().into_inner();
+        if let Some(child) = children.next() {
+            if children.next().is_none() {
+                return Some(self.with_pair(child));
+            }
+        }
+        None
+    }
+
+    pub fn user_data(&self) -> &'data Data {
+        self.user_data
+    }
+    pub fn as_pair(&self) -> &Pair<'input, Rule> {
+        &self.pair
+    }
+    pub fn as_span(&self) -> Span<'input> {
+        self.pair.as_span()
+    }
+    pub fn as_str(&self) -> &'input str {
+        self.pair.as_str()
+    }
+    pub fn as_rule(&self) -> Rule {
+        self.pair.as_rule()
+    }
+}
+
+/// Used by the macros.
+pub trait PestConsumer {
+    type Rule: pest::RuleType;
+    fn rule_alias(rule: Self::Rule) -> String;
+    fn allows_shortcut(rule: Self::Rule) -> bool;
+}
+
+/// Pretty-print a pair and its nested children.
+fn debug_pair<Rule: pest::RuleType>(pair: Pair<Rule>) -> String {
+    use std::fmt::Write;
+    let mut s = String::new();
+    fn aux<Rule: pest::RuleType>(
+        s: &mut String,
+        indent: usize,
+        prefix: String,
+        pair: Pair<Rule>,
+    ) {
+        let indent_str = "| ".repeat(indent);
+        let rule = pair.as_rule();
+        let contents = pair.as_str();
+        let mut inner = pair.into_inner();
+        let mut first = true;
+        while let Some(p) = inner.next() {
+            if first {
+                first = false;
+                let last = inner.peek().is_none();
+                if last && p.as_str() == contents {
+                    let prefix = format!("{}{:?} > ", prefix, rule);
+                    aux(s, indent, prefix, p);
+                    continue;
+                } else {
+                    writeln!(
+                        s,
+                        r#"{}{}{:?}: "{}""#,
+                        indent_str, prefix, rule, contents
+                    )
+                    .unwrap();
+                }
+            }
+            aux(s, indent + 1, "".into(), p);
+        }
+        if first {
+            writeln!(
+                s,
+                r#"{}{}{:?}: "{}""#,
+                indent_str, prefix, rule, contents
+            )
+            .unwrap();
+        }
+    }
+    aux(&mut s, 0, "".into(), pair);
+    s
+}