feat: Add format! macro

Author: bch29

src/format_macro.rs

@@ -0,0 +1,300 @@
+//! Implementation of the `format!` macro
+use gluon_codegen::Trace;
+
+use crate::{
+    base::{
+        ast::{self, AstClone, SpannedExpr},
+        pos,
+        symbol::{Symbol, Symbols},
+        types::TypeCache,
+    },
+    parser::parse_expr,
+    vm::macros::{self, Error, Macro, MacroExpander, MacroFuture, MacroResult},
+};
+
+/**
+ * Format macro with expressions embedded in the format string.
+ *
+ * ```ignore
+ * let x = 1
+ * let foo = "foo"
+ * format! "x is {x}, x + 1 is {x+1}, foo is {foo} and {foo:?}"
+ * ```
+ *
+ *   ==> x is 1, x + 1 is 2, foo is foo and "foo"
+ */
+#[derive(Trace)]
+#[gluon(crate_name = "vm")]
+pub struct Format;
+
+fn expr_from_path<'ast>(
+    arena: &mut ast::OwnedArena<'ast, Symbol>,
+    symbols: &mut Symbols,
+    span: pos::Span<pos::ByteIndex>,
+    path_head: &str,
+    path_tail: &[&str],
+) -> SpannedExpr<'ast, Symbol> {
+    let mut head = pos::spanned(
+        span,
+        ast::Expr::Ident(ast::TypedIdent::new(symbols.simple_symbol(path_head))),
+    );
+
+    for &item in path_tail {
+        head = pos::spanned(
+            span,
+            ast::Expr::Projection(
+                arena.alloc(head),
+                symbols.simple_symbol(item),
+                Default::default(),
+            ),
+        );
+    }
+
+    head
+}
+
+async fn run_import<'a, 'ast>(
+    importer: &dyn Macro,
+    env: &mut MacroExpander<'a>,
+    symbols: &mut Symbols,
+    arena: &mut ast::OwnedArena<'ast, Symbol>,
+    span: pos::Span<pos::ByteIndex>,
+    path: &[&str],
+) -> MacroResult<'ast> {
+    let (path_head, path_tail) = match path {
+        [head, tail @ ..] => (head, tail),
+        _ => return Err(Error::message("run_import for empty path")),
+    };
+
+    let path = expr_from_path(arena, symbols, span, path_head, path_tail);
+    let args = arena.alloc_extend(vec![path]);
+
+    match importer.expand(env, symbols, arena, args).await? {
+        macros::LazyMacroResult::Done(res) => Ok(res),
+        macros::LazyMacroResult::Lazy(f) => f().await,
+    }
+}
+
+impl Macro for Format {
+    fn expand<'r, 'a: 'r, 'b: 'r, 'c: 'r, 'ast: 'r>(
+        &self,
+        env: &'b mut MacroExpander<'a>,
+        symbols: &'c mut Symbols,
+        arena: &'b mut ast::OwnedArena<'ast, Symbol>,
+        args: &'b mut [SpannedExpr<'ast, Symbol>],
+    ) -> MacroFuture<'r, 'ast> {
+        Box::pin(async move {
+            let arg = match args {
+                [arg] => (arg),
+                _ => return Err(Error::message(format!("format! expects 1 argument"))),
+            };
+
+            let span = arg.span;
+            let sp = |e: ast::Expr<'ast, Symbol>| pos::spanned(span, e);
+
+            let import = env
+                .vm
+                .get_macros()
+                .get("import")
+                .ok_or_else(|| Error::message(format!("format! cannot find import macro")))?;
+
+            let show_module =
+                run_import(&*import, env, symbols, arena, span, &["std", "show"]).await?;
+            let show_module = arena.alloc(show_module);
+            let show_func = arena.alloc(sp(ast::Expr::Projection(
+                show_module,
+                symbols.simple_symbol("show"),
+                Default::default(),
+            )));
+
+            let display_module =
+                run_import(&*import, env, symbols, arena, span, &["std", "display"]).await?;
+            let display_module = arena.alloc(display_module);
+            let display_func = sp(ast::Expr::Projection(
+                display_module,
+                symbols.simple_symbol("display"),
+                Default::default(),
+            ));
+
+            let semigroup_module =
+                run_import(&*import, env, symbols, arena, span, &["std", "semigroup"]).await?;
+            let semigroup_module = arena.alloc(semigroup_module);
+            let append_func = sp(ast::Expr::Projection(
+                semigroup_module,
+                symbols.simple_symbol("append"),
+                Default::default(),
+            ));
+
+            let format_string = match &arg.value {
+                ast::Expr::Literal(ast::Literal::String(text)) => text,
+                _ => return Err(Error::message(format!("format! expects a string argument"))),
+            };
+
+            let app1 = |func: &ast::SpannedExpr<'ast, Symbol>, e: ast::SpannedExpr<'ast, Symbol>| {
+                let func = arena.alloc(func.ast_clone(arena.borrow()));
+
+                sp(ast::Expr::App {
+                    func,
+                    implicit_args: arena.alloc_extend(vec![]),
+                    args: arena.alloc_extend(vec![e]),
+                })
+            };
+
+            let app_exprs = |lhs, rhs| {
+                let func = arena.alloc(append_func.ast_clone(arena.borrow()));
+
+                sp(ast::Expr::App {
+                    func,
+                    implicit_args: arena.alloc_extend(vec![]),
+                    args: arena.alloc_extend(vec![lhs, rhs]),
+                })
+            };
+
+            let literal_expr = |val: String| sp(ast::Expr::Literal(ast::Literal::String(val)));
+
+            let type_cache = TypeCache::new();
+
+            let mut remaining = format_string.as_str();
+
+            let mut result_expr = None;
+
+            while let Some(find_result) = find_expr(remaining)? {
+                remaining = find_result.remaining;
+
+                let sub_expr = {
+                    let value = parse_expr(
+                        arena.borrow(),
+                        symbols,
+                        &type_cache,
+                        find_result.expr.expr,
+                    )
+                    .map_err(|err| {
+                        Error::message(format!("format! could not parse subexpression: {}", err))
+                    })?
+                    .value;
+
+                    pos::spanned(
+                        span.subspan(
+                            pos::ByteOffset(find_result.expr_start as i64),
+                            pos::ByteOffset(find_result.expr_end as i64),
+                        ),
+                        value,
+                    )
+                };
+
+                let formatted_sub_expr = match find_result.expr.modifier {
+                    FormatModifier::Display => app1(&display_func, sub_expr),
+                    FormatModifier::Debug => app1(&show_func, sub_expr),
+                };
+
+                let part_expr = app_exprs(
+                    literal_expr(find_result.prefix.to_owned()),
+                    formatted_sub_expr,
+                );
+
+                result_expr = match result_expr.take() {
+                    None => Some(part_expr),
+                    Some(prev_expr) => Some(app_exprs(prev_expr, part_expr)),
+                };
+            }
+
+            let result_expr = match result_expr.take() {
+                None => literal_expr(remaining.to_owned()),
+                Some(result_expr) => {
+                    if remaining.is_empty() {
+                        result_expr
+                    } else {
+                        app_exprs(result_expr, literal_expr(remaining.to_owned()))
+                    }
+                }
+            };
+
+            Ok(result_expr.into())
+        })
+    }
+}
+
+const OPEN_BRACE: &'static str = "{";
+const CLOSE_BRACE: &'static str = "}";
+
+enum FormatModifier {
+    Display,
+    Debug,
+}
+
+struct FormatExpr<'a> {
+    expr: &'a str,
+    modifier: FormatModifier,
+}
+
+struct FindExprResult<'a> {
+    prefix: &'a str,
+    expr: FormatExpr<'a>,
+    remaining: &'a str,
+    expr_start: usize,
+    expr_end: usize,
+}
+
+fn parse_format_expr<'a>(contents: &'a str) -> Result<FormatExpr<'a>, Error> {
+    let mut split_iter = contents.split(":");
+
+    match (split_iter.next(), split_iter.next(), split_iter.next()) {
+        (Some(expr), Some(fmt), None) => {
+            if fmt == "?" {
+                Ok(FormatExpr {
+                    expr,
+                    modifier: FormatModifier::Debug,
+                })
+            } else {
+                Err(Error::message(format!(
+                    "Unrecognized format specifier: {}",
+                    fmt
+                )))
+            }
+        }
+        (Some(expr), None, None) => Ok(FormatExpr {
+            expr,
+            modifier: FormatModifier::Display,
+        }),
+        _ => Err(Error::message(format!(
+            "At most one colon allowed in format subexpression",
+        ))),
+    }
+}
+
+fn find_expr<'a>(format_str: &'a str) -> Result<Option<FindExprResult<'a>>, Error> {
+    let open_ix = match format_str.find(OPEN_BRACE) {
+        None => return Ok(None),
+        Some(ix) => ix,
+    };
+
+    let close_ix = match format_str.find(CLOSE_BRACE) {
+        Some(ix) if ix < open_ix => {
+            return Err(Error::message(format!(
+                "Mismatched braces in format! string"
+            )))
+        }
+        None => 
+            return Err(Error::message(format!(
+                "Mismatched braces in format! string"
+            ))),
+        Some(ix) => ix,
+    };
+
+    let prefix = &format_str[..open_ix];
+    let expr_start = OPEN_BRACE.len() + open_ix;
+    let expr_end = close_ix;
+    let brace_end = close_ix + CLOSE_BRACE.len();
+
+    let expr = parse_format_expr(&format_str[expr_start..expr_end])?;
+
+    let remaining = &format_str[brace_end..];
+
+    Ok(Some(FindExprResult {
+        prefix,
+        expr,
+        remaining,
+        expr_start,
+        expr_end,
+    }))
+}

src/lib.rs

@@ -49,6 +49,7 @@ pub mod compiler_pipeline;
 #[macro_use]
 pub mod import;
 pub mod lift_io;
+pub mod format_macro;
 #[doc(hidden)]
 pub mod query;
 pub mod std_lib;
@@ -958,6 +959,8 @@ impl VmBuilder {
             }
 
             macros.insert(String::from("lift_io"), lift_io::LiftIo);
+
+            macros.insert(String::from("format"), format_macro::Format);
         }
 
         add_extern_module_with_deps(