1 files changed, 116 insertions, 0 deletions
diff --git a/rprt-engine/src/expression.rs b/rprt-engine/src/expression.rs
new file mode 100644
index 0000000..68849cb
--- /dev/null
+++ b/rprt-engine/src/expression.rs
@@ -0,0 +1,116 @@
+#[derive(Debug, Clone, PartialEq)]
+pub enum SelectionValuedExpr {
+    // Nullary selection function application
+    NullaryApplicationS(SelectionFn),
+    NullaryApplicationT(TextFn),
+
+    // Monadic selection function application: α F
+    MonadicApplicationS {
+        arg: Box<SelectionValuedExpr>,
+        func: SelectionFn,
+    },
+    // Monadic selection function application: F τ
+    MonadicApplicationT {
+        arg: Box<TextValuedExpr>,
+        func: TextFn,
+    },
+
+    // Dyadic selection function application: α F β
+    DyadicApplicationS {
+        left: Box<SelectionValuedExpr>,
+        right: Box<SelectionValuedExpr>,
+        func: SelectionFn,
+    },
+    // Dyadic text function application: α F τ
+    DyadicApplicationT {
+        left: Box<SelectionValuedExpr>,
+        right: Box<SelectionValuedExpr>,
+        func: SelectionFn,
+    },
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub enum TextValuedExpr {
+    // Selection coerced to text (implicit coercion)
+    FromSelection(Box<SelectionValuedExpr>),
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub enum SelectionFn {
+    Function {
+        func: BuiltinSelectionFn,
+        search_mod: Option<SearchModifier>,
+        result_transform: Option<ResultTransform>,
+    },
+
+    Hook {
+        kind: HookKind,
+        left: Box<SelectionFn>,
+        right: Box<SelectionFn>,
+    },
+
+    Train(Vec<SelectionFn>),
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub enum TextFn {
+    Function {
+        func: BuiltinTextFn,
+        swapped: bool,
+    },
+
+    Hook {
+        kind: HookKind,
+        left: Box<TextFn>,
+        right: Box<TextFn>,
+    },
+
+    Train(Vec<TextFn>),
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub enum BuiltinSelectionFn {
+    Empty,               // e
+    EndOfBuffer,         // $
+    Span,                // -
+    CharOffset(usize),   // # (expects number arg)
+    Line(usize),         // (expects number arg)
+    Regex(String),       // /re/ (expects regex arg)
+    AllMatches(String),  // x (expects /re/ arg)
+    RelativeLine(usize), // + (expects number arg)
+    BufferMatch(String), // B (expects /re/ arg)
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub enum BuiltinTextFn {
+    Dot,             // .
+    Change,          // c
+    Insert,          // i
+    Append,          // a
+    Delete,          // d
+    Write,           // w
+    Pipe,            // |
+    Literal(String), // "..."
+}
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub enum SearchModifier {
+    Reverse,           // '
+    Sequential,        // ;
+    ReverseSequential, // ';
+    SequentialReverse, // ;'
+}
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub enum ResultTransform {
+    Complement,            // ~
+    Conditional,           // ?
+    ComplementConditional, // ~?
+    ConditionalComplement, // ?~
+}
+
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub enum HookKind {
+    Before, // F>G (left hook)
+    After,  // F<G (right hook)
+}