Resolve functions (#550)

Modifies parsing to return strongly-typed `Thunk`s, which contain both the function implementation, as well as the correct number of arguments. This moves unknown function and function argument count mismatch errors to parse time.
2019-11-21 12:14:10 -06:00 · 2019-11-21 12:14:10 -06:00 · d2decbfdb8
commit d2decbfdb8
parent ba93c5e6af
13 changed files with 333 additions and 215 deletions
--- a/Cargo.lock
+++ b/Cargo.lock
@ -113,6 +113,16 @@ dependencies = [
 "winapi 0.3.8 (registry+https://github.com/rust-lang/crates.io-index)",
 ]

+[[package]]
+name = "derivative"
+version = "1.0.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "proc-macro2 0.4.30 (registry+https://github.com/rust-lang/crates.io-index)",
+ "quote 0.6.13 (registry+https://github.com/rust-lang/crates.io-index)",
+ "syn 0.15.44 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "difference"
 version = "2.0.0"
@ -198,6 +208,7 @@ dependencies = [
 "atty 0.2.13 (registry+https://github.com/rust-lang/crates.io-index)",
 "clap 2.33.0 (registry+https://github.com/rust-lang/crates.io-index)",
 "ctrlc 3.1.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "derivative 1.0.3 (registry+https://github.com/rust-lang/crates.io-index)",
 "dotenv 0.15.0 (registry+https://github.com/rust-lang/crates.io-index)",
 "edit-distance 2.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
 "env_logger 0.7.1 (registry+https://github.com/rust-lang/crates.io-index)",
@ -274,6 +285,14 @@ dependencies = [
 "output_vt100 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
 ]

+[[package]]
+name = "proc-macro2"
+version = "0.4.30"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "unicode-xid 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "proc-macro2"
 version = "1.0.6"
@ -287,6 +306,14 @@ name = "quick-error"
 version = "1.2.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"

+[[package]]
+name = "quote"
+version = "0.6.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "proc-macro2 0.4.30 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "quote"
 version = "1.0.2"
@ -390,6 +417,16 @@ name = "strsim"
 version = "0.8.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"

+[[package]]
+name = "syn"
+version = "0.15.44"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "proc-macro2 0.4.30 (registry+https://github.com/rust-lang/crates.io-index)",
+ "quote 0.6.13 (registry+https://github.com/rust-lang/crates.io-index)",
+ "unicode-xid 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "syn"
 version = "1.0.8"
@ -454,6 +491,11 @@ name = "unicode-width"
 version = "0.1.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"

+[[package]]
+name = "unicode-xid"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "unicode-xid"
 version = "0.2.0"
@ -534,6 +576,7 @@ dependencies = [
 "checksum clap 2.33.0 (registry+https://github.com/rust-lang/crates.io-index)" = "5067f5bb2d80ef5d68b4c87db81601f0b75bca627bc2ef76b141d7b846a3c6d9"
 "checksum ctor 0.1.12 (registry+https://github.com/rust-lang/crates.io-index)" = "cd8ce37ad4184ab2ce004c33bf6379185d3b1c95801cab51026bd271bf68eedc"
 "checksum ctrlc 3.1.3 (registry+https://github.com/rust-lang/crates.io-index)" = "c7dfd2d8b4c82121dfdff120f818e09fc4380b0b7e17a742081a89b94853e87f"
+"checksum derivative 1.0.3 (registry+https://github.com/rust-lang/crates.io-index)" = "942ca430eef7a3806595a6737bc388bf51adb888d3fc0dd1b50f1c170167ee3a"
 "checksum difference 2.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "524cbf6897b527295dff137cec09ecf3a05f4fddffd7dfcd1585403449e74198"
 "checksum doc-comment 0.3.1 (registry+https://github.com/rust-lang/crates.io-index)" = "923dea538cea0aa3025e8685b20d6ee21ef99c4f77e954a30febbaac5ec73a97"
 "checksum dotenv 0.15.0 (registry+https://github.com/rust-lang/crates.io-index)" = "77c90badedccf4105eca100756a0b1289e191f6fcbdadd3cee1d2f614f97da8f"
@ -553,8 +596,10 @@ dependencies = [
 "checksum output_vt100 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)" = "53cdc5b785b7a58c5aad8216b3dfa114df64b0b06ae6e1501cef91df2fbdf8f9"
 "checksum ppv-lite86 0.2.6 (registry+https://github.com/rust-lang/crates.io-index)" = "74490b50b9fbe561ac330df47c08f3f33073d2d00c150f719147d7c54522fa1b"
 "checksum pretty_assertions 0.6.1 (registry+https://github.com/rust-lang/crates.io-index)" = "3f81e1644e1b54f5a68959a29aa86cde704219254669da328ecfdf6a1f09d427"
+"checksum proc-macro2 0.4.30 (registry+https://github.com/rust-lang/crates.io-index)" = "cf3d2011ab5c909338f7887f4fc896d35932e29146c12c8d01da6b22a80ba759"
 "checksum proc-macro2 1.0.6 (registry+https://github.com/rust-lang/crates.io-index)" = "9c9e470a8dc4aeae2dee2f335e8f533e2d4b347e1434e5671afc49b054592f27"
 "checksum quick-error 1.2.2 (registry+https://github.com/rust-lang/crates.io-index)" = "9274b940887ce9addde99c4eee6b5c44cc494b182b97e73dc8ffdcb3397fd3f0"
+"checksum quote 0.6.13 (registry+https://github.com/rust-lang/crates.io-index)" = "6ce23b6b870e8f94f81fb0a363d65d86675884b34a09043c81e5562f11c1f8e1"
 "checksum quote 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)" = "053a8c8bcc71fcce321828dc897a98ab9760bef03a4fc36693c231e5b3216cfe"
 "checksum rand 0.7.2 (registry+https://github.com/rust-lang/crates.io-index)" = "3ae1b169243eaf61759b8475a998f0a385e42042370f3a7dbaf35246eacc8412"
 "checksum rand_chacha 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "03a2a90da8c7523f554344f921aa97283eadf6ac484a6d2a7d0212fa7f8d6853"
@ -568,6 +613,7 @@ dependencies = [
 "checksum snafu 0.6.0 (registry+https://github.com/rust-lang/crates.io-index)" = "41207ca11f96a62cd34e6b7fdf73d322b25ae3848eb9d38302169724bb32cf27"
 "checksum snafu-derive 0.6.0 (registry+https://github.com/rust-lang/crates.io-index)" = "4c5e338c8b0577457c9dda8e794b6ad7231c96e25b1b0dd5842d52249020c1c0"
 "checksum strsim 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)" = "8ea5119cdb4c55b55d432abb513a0429384878c15dde60cc77b1c99de1a95a6a"
+"checksum syn 0.15.44 (registry+https://github.com/rust-lang/crates.io-index)" = "9ca4b3b69a77cbe1ffc9e198781b7acb0c7365a883670e8f1c1bc66fba79a5c5"
 "checksum syn 1.0.8 (registry+https://github.com/rust-lang/crates.io-index)" = "661641ea2aa15845cddeb97dad000d22070bb5c1fb456b96c1cba883ec691e92"
 "checksum target 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "10000465bb0cc031c87a44668991b284fd84c0e6bd945f62d4af04e9e52a222a"
 "checksum tempfile 3.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "7a6e24d9338a0a5be79593e2fa15a648add6138caa803e2d5bc782c371732ca9"
@ -575,6 +621,7 @@ dependencies = [
 "checksum textwrap 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)" = "d326610f408c7a4eb6f51c37c330e496b08506c9457c9d34287ecc38809fb060"
 "checksum thread_local 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)" = "c6b53e329000edc2b34dbe8545fd20e55a333362d0a321909685a19bd28c3f1b"
 "checksum unicode-width 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)" = "7007dbd421b92cc6e28410fe7362e2e0a2503394908f417b68ec8d1c364c4e20"
+"checksum unicode-xid 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "fc72304796d0818e357ead4e000d19c9c174ab23dc11093ac919054d20a6a7fc"
 "checksum unicode-xid 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "826e7639553986605ec5979c7dd957c7895e93eabed50ab2ffa7f6128a75097c"
 "checksum vec_map 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)" = "05c78687fb1a80548ae3250346c3db86a80a7cdd77bda190189f2d0a0987c81a"
 "checksum void 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)" = "6a02e4885ed3bc0f2de90ea6dd45ebcbb66dacffe03547fadbb0eeae2770887d"
--- a/Cargo.toml
+++ b/Cargo.toml
@ -19,6 +19,7 @@ ansi_term      = "0.12"
 assert_matches = "1"
 atty           = "0.2"
 clap           = "2.33"
+derivative     = "1"
 dotenv         = "0.15"
 edit-distance  = "2"
 env_logger     = "0.7"
--- a/src/assignment_evaluator.rs
+++ b/src/assignment_evaluator.rs
@ -101,20 +101,47 @@ impl<'a, 'b> AssignmentEvaluator<'a, 'b> {
          })
        }
      }
-      Expression::Call {
-        function,
-        arguments: call_arguments,
-      } => {
-        let call_arguments = call_arguments
-          .iter()
-          .map(|argument| self.evaluate_expression(argument, arguments))
-          .collect::<Result<Vec<String>, RuntimeError>>()?;
+      Expression::Call { thunk } => {
        let context = FunctionContext {
          invocation_directory: &self.config.invocation_directory,
          working_directory: &self.working_directory,
          dotenv: self.dotenv,
        };
-        Function::evaluate(*function, &context, &call_arguments)
+
+        use Thunk::*;
+        match thunk {
+          Nullary { name, function, .. } => {
+            function(&context).map_err(|message| RuntimeError::FunctionCall {
+              function: *name,
+              message,
+            })
+          }
+          Unary {
+            name,
+            function,
+            arg,
+            ..
+          } => function(&context, &self.evaluate_expression(arg, arguments)?).map_err(|message| {
+            RuntimeError::FunctionCall {
+              function: *name,
+              message,
+            }
+          }),
+          Binary {
+            name,
+            function,
+            args: [a, b],
+            ..
+          } => function(
+            &context,
+            &self.evaluate_expression(a, arguments)?,
+            &self.evaluate_expression(b, arguments)?,
+          )
+          .map_err(|message| RuntimeError::FunctionCall {
+            function: *name,
+            message,
+          }),
+        }
      }
      Expression::StringLiteral { string_literal } => Ok(string_literal.cooked.to_string()),
      Expression::Backtick { contents, token } => {
--- a/src/assignment_resolver.rs
+++ b/src/assignment_resolver.rs
@ -61,32 +61,35 @@ impl<'a: 'b, 'b> AssignmentResolver<'a, 'b> {
      Expression::Variable { name } => {
        let variable = name.lexeme();
        if self.evaluated.contains(variable) {
-          return Ok(());
+          Ok(())
        } else if self.seen.contains(variable) {
          let token = self.assignments[variable].name.token();
          self.stack.push(variable);
-          return Err(token.error(CircularVariableDependency {
+          Err(token.error(CircularVariableDependency {
            variable,
            circle: self.stack.clone(),
-          }));
+          }))
        } else if self.assignments.contains_key(variable) {
-          self.resolve_assignment(variable)?;
+          self.resolve_assignment(variable)
        } else {
-          return Err(name.token().error(UndefinedVariable { variable }));
+          Err(name.token().error(UndefinedVariable { variable }))
        }
      }
-      Expression::Call {
-        function,
-        arguments,
-      } => Function::resolve(&function.token(), arguments.len())?,
+      Expression::Call { thunk } => match thunk {
+        Thunk::Nullary { .. } => Ok(()),
+        Thunk::Unary { arg, .. } => self.resolve_expression(arg),
+        Thunk::Binary { args: [a, b], .. } => {
+          self.resolve_expression(a)?;
+          self.resolve_expression(b)
+        }
+      },
      Expression::Concatination { lhs, rhs } => {
        self.resolve_expression(lhs)?;
-        self.resolve_expression(rhs)?;
+        self.resolve_expression(rhs)
      }
-      Expression::StringLiteral { .. } | Expression::Backtick { .. } => {}
-      Expression::Group { contents } => self.resolve_expression(contents)?,
+      Expression::StringLiteral { .. } | Expression::Backtick { .. } => Ok(()),
+      Expression::Group { contents } => self.resolve_expression(contents),
    }
-    Ok(())
  }
 }

@ -125,12 +128,32 @@ mod tests {
  }

  analysis_error! {
-    name:   unknown_function,
-    input:  "a = foo()",
-    offset:  4,
+    name:   unknown_function_parameter,
+    input:  "x := env_var(yy)",
+    offset:  13,
    line:   0,
-    column: 4,
-    width:  3,
-    kind:   UnknownFunction{function: "foo"},
+    column: 13,
+    width:  2,
+    kind:   UndefinedVariable{variable: "yy"},
+  }
+
+  analysis_error! {
+    name:   unknown_function_parameter_binary_first,
+    input:  "x := env_var_or_default(yy, 'foo')",
+    offset:  24,
+    line:   0,
+    column: 24,
+    width:  2,
+    kind:   UndefinedVariable{variable: "yy"},
+  }
+
+  analysis_error! {
+    name:   unknown_function_parameter_binary_second,
+    input:  "x := env_var_or_default('foo', yy)",
+    offset:  31,
+    line:   0,
+    column: 31,
+    width:  2,
+    kind:   UndefinedVariable{variable: "yy"},
  }
 }
--- a/src/common.rs
+++ b/src/common.rs
@ -4,7 +4,7 @@ pub(crate) use std::{
  cmp,
  collections::{BTreeMap, BTreeSet},
  env,
-  fmt::{self, Display, Formatter},
+  fmt::{self, Debug, Display, Formatter},
  fs,
  io::{self, Write},
  iter::{self, FromIterator},
@ -26,6 +26,7 @@ pub(crate) use crate::testing;
 pub(crate) use crate::{node::Node, tree::Tree};

 // dependencies
+pub(crate) use derivative::Derivative;
 pub(crate) use edit_distance::edit_distance;
 pub(crate) use libc::EXIT_FAILURE;
 pub(crate) use log::warn;
@ -52,15 +53,15 @@ pub(crate) use crate::{
  compilation_error::CompilationError, compilation_error_kind::CompilationErrorKind,
  compiler::Compiler, config::Config, config_error::ConfigError, count::Count,
  dependency::Dependency, enclosure::Enclosure, expression::Expression, fragment::Fragment,
-  function::Function, function_context::FunctionContext, functions::Functions,
-  interrupt_guard::InterruptGuard, interrupt_handler::InterruptHandler, item::Item,
-  justfile::Justfile, lexer::Lexer, line::Line, list::List, load_error::LoadError, module::Module,
-  name::Name, output_error::OutputError, parameter::Parameter, parser::Parser, platform::Platform,
-  position::Position, positional::Positional, recipe::Recipe, recipe_context::RecipeContext,
+  function::Function, function_context::FunctionContext, interrupt_guard::InterruptGuard,
+  interrupt_handler::InterruptHandler, item::Item, justfile::Justfile, lexer::Lexer, line::Line,
+  list::List, load_error::LoadError, module::Module, name::Name, output_error::OutputError,
+  parameter::Parameter, parser::Parser, platform::Platform, position::Position,
+  positional::Positional, recipe::Recipe, recipe_context::RecipeContext,
  recipe_resolver::RecipeResolver, runtime_error::RuntimeError, search::Search,
  search_config::SearchConfig, search_error::SearchError, set::Set, setting::Setting,
  settings::Settings, shebang::Shebang, show_whitespace::ShowWhitespace, state::State,
-  string_literal::StringLiteral, subcommand::Subcommand, table::Table, token::Token,
+  string_literal::StringLiteral, subcommand::Subcommand, table::Table, thunk::Thunk, token::Token,
  token_kind::TokenKind, use_color::UseColor, variables::Variables, verbosity::Verbosity,
  warning::Warning,
 };
--- a/src/expression.rs
+++ b/src/expression.rs
@ -14,10 +14,7 @@ pub(crate) enum Expression<'src> {
    token: Token<'src>,
  },
  /// `name(arguments)`
-  Call {
-    function: Name<'src>,
-    arguments: Vec<Expression<'src>>,
-  },
+  Call { thunk: Thunk<'src> },
  /// `lhs + rhs`
  Concatination {
    lhs: Box<Expression<'src>>,
@ -35,35 +32,17 @@ impl<'src> Expression<'src> {
  pub(crate) fn variables<'expression>(&'expression self) -> Variables<'expression, 'src> {
    Variables::new(self)
  }
-
-  pub(crate) fn functions<'expression>(&'expression self) -> Functions<'expression, 'src> {
-    Functions::new(self)
-  }
 }

 impl<'src> Display for Expression<'src> {
  fn fmt(&self, f: &mut Formatter) -> Result<(), fmt::Error> {
    match self {
-      Expression::Backtick { contents, .. } => write!(f, "`{}`", contents)?,
-      Expression::Concatination { lhs, rhs } => write!(f, "{} + {}", lhs, rhs)?,
-      Expression::StringLiteral { string_literal } => write!(f, "{}", string_literal)?,
-      Expression::Variable { name } => write!(f, "{}", name.lexeme())?,
-      Expression::Call {
-        function,
-        arguments,
-      } => {
-        write!(f, "{}(", function.lexeme())?;
-        for (i, argument) in arguments.iter().enumerate() {
-          if i > 0 {
-            write!(f, ", {}", argument)?;
-          } else {
-            write!(f, "{}", argument)?;
-          }
-        }
-        write!(f, ")")?;
-      }
-      Expression::Group { contents } => write!(f, "({})", contents)?,
+      Expression::Backtick { contents, .. } => write!(f, "`{}`", contents),
+      Expression::Concatination { lhs, rhs } => write!(f, "{} + {}", lhs, rhs),
+      Expression::StringLiteral { string_literal } => write!(f, "{}", string_literal),
+      Expression::Variable { name } => write!(f, "{}", name.lexeme()),
+      Expression::Call { thunk } => write!(f, "{}", thunk),
+      Expression::Group { contents } => write!(f, "({})", contents),
    }
-    Ok(())
  }
 }
--- a/src/function.rs
+++ b/src/function.rs
@ -2,8 +2,14 @@ use crate::common::*;

 use target;

+pub(crate) enum Function {
+  Nullary(fn(&FunctionContext) -> Result<String, String>),
+  Unary(fn(&FunctionContext, &str) -> Result<String, String>),
+  Binary(fn(&FunctionContext, &str, &str) -> Result<String, String>),
+}
+
 lazy_static! {
-  static ref FUNCTIONS: BTreeMap<&'static str, Function> = vec![
+  pub(crate) static ref TABLE: BTreeMap<&'static str, Function> = vec![
    ("arch", Function::Nullary(arch)),
    ("os", Function::Nullary(os)),
    ("os_family", Function::Nullary(os_family)),
@ -18,14 +24,8 @@ lazy_static! {
  .collect();
 }

-pub(crate) enum Function {
-  Nullary(fn(&FunctionContext) -> Result<String, String>),
-  Unary(fn(&FunctionContext, &str) -> Result<String, String>),
-  Binary(fn(&FunctionContext, &str, &str) -> Result<String, String>),
-}
-
 impl Function {
-  fn argc(&self) -> usize {
+  pub(crate) fn argc(&self) -> usize {
    use self::Function::*;
    match *self {
      Nullary(_) => 0,
@ -33,85 +33,26 @@ impl Function {
      Binary(_) => 2,
    }
  }
-
-  pub(crate) fn resolve<'a>(token: &Token<'a>, argc: usize) -> CompilationResult<'a, ()> {
-    let name = token.lexeme();
-    if let Some(function) = FUNCTIONS.get(&name) {
-      use self::Function::*;
-      match (function, argc) {
-        (&Nullary(_), 0) | (&Unary(_), 1) | (&Binary(_), 2) => Ok(()),
-        _ => Err(
-          token.error(CompilationErrorKind::FunctionArgumentCountMismatch {
-            function: name,
-            found: argc,
-            expected: function.argc(),
-          }),
-        ),
-      }
-    } else {
-      Err(token.error(CompilationErrorKind::UnknownFunction {
-        function: token.lexeme(),
-      }))
-    }
-  }
-
-  pub(crate) fn evaluate<'a>(
-    function_name: Name<'a>,
-    context: &FunctionContext,
-    arguments: &[String],
-  ) -> RunResult<'a, String> {
-    let name = function_name.lexeme();
-    if let Some(function) = FUNCTIONS.get(name) {
-      use self::Function::*;
-      let argc = arguments.len();
-      match (function, argc) {
-        (&Nullary(f), 0) => f(context).map_err(|message| RuntimeError::FunctionCall {
-          function: function_name,
-          message,
-        }),
-        (&Unary(f), 1) => f(context, &arguments[0]).map_err(|message| RuntimeError::FunctionCall {
-          function: function_name,
-          message,
-        }),
-        (&Binary(f), 2) => {
-          f(context, &arguments[0], &arguments[1]).map_err(|message| RuntimeError::FunctionCall {
-            function: function_name,
-            message,
-          })
-        }
-        _ => Err(RuntimeError::Internal {
-          message: format!(
-            "attempted to evaluate function `{}` with {} arguments",
-            name, argc
-          ),
-        }),
-      }
-    } else {
-      Err(RuntimeError::Internal {
-        message: format!("attempted to evaluate unknown function: `{}`", name),
-      })
-    }
-  }
 }

-pub(crate) fn arch(_context: &FunctionContext) -> Result<String, String> {
+fn arch(_context: &FunctionContext) -> Result<String, String> {
  Ok(target::arch().to_string())
 }

-pub(crate) fn os(_context: &FunctionContext) -> Result<String, String> {
+fn os(_context: &FunctionContext) -> Result<String, String> {
  Ok(target::os().to_string())
 }

-pub(crate) fn os_family(_context: &FunctionContext) -> Result<String, String> {
+fn os_family(_context: &FunctionContext) -> Result<String, String> {
  Ok(target::os_family().to_string())
 }

-pub(crate) fn invocation_directory(context: &FunctionContext) -> Result<String, String> {
+fn invocation_directory(context: &FunctionContext) -> Result<String, String> {
  Platform::to_shell_path(context.working_directory, context.invocation_directory)
    .map_err(|e| format!("Error getting shell path: {}", e))
 }

-pub(crate) fn env_var(context: &FunctionContext, key: &str) -> Result<String, String> {
+fn env_var(context: &FunctionContext, key: &str) -> Result<String, String> {
  use std::env::VarError::*;

  if let Some(value) = context.dotenv.get(key) {
@ -128,7 +69,7 @@ pub(crate) fn env_var(context: &FunctionContext, key: &str) -> Result<String, St
  }
 }

-pub(crate) fn env_var_or_default(
+fn env_var_or_default(
  context: &FunctionContext,
  key: &str,
  default: &str,
--- a/src/functions.rs
+++ b/src/functions.rs
@ -1,38 +0,0 @@
-use crate::common::*;
-
-pub(crate) struct Functions<'expression, 'src> {
-  stack: Vec<&'expression Expression<'src>>,
-}
-
-impl<'expression, 'src> Functions<'expression, 'src> {
-  pub(crate) fn new(root: &'expression Expression<'src>) -> Functions<'expression, 'src> {
-    Functions { stack: vec![root] }
-  }
-}
-
-impl<'expression, 'src> Iterator for Functions<'expression, 'src> {
-  type Item = (Token<'src>, usize);
-
-  fn next(&mut self) -> Option<Self::Item> {
-    match self.stack.pop() {
-      None
-      | Some(Expression::StringLiteral { .. })
-      | Some(Expression::Backtick { .. })
-      | Some(Expression::Variable { .. }) => None,
-      Some(Expression::Call {
-        function,
-        arguments,
-        ..
-      }) => Some((function.token(), arguments.len())),
-      Some(Expression::Concatination { lhs, rhs }) => {
-        self.stack.push(lhs);
-        self.stack.push(rhs);
-        self.next()
-      }
-      Some(Expression::Group { contents }) => {
-        self.stack.push(contents);
-        self.next()
-      }
-    }
-  }
-}
--- a/src/lib.rs
+++ b/src/lib.rs
@ -40,7 +40,6 @@ mod expression;
 mod fragment;
 mod function;
 mod function_context;
-mod functions;
 mod interrupt_guard;
 mod interrupt_handler;
 mod item;
@ -81,6 +80,7 @@ mod state;
 mod string_literal;
 mod subcommand;
 mod table;
+mod thunk;
 mod token;
 mod token_kind;
 mod use_color;
--- a/src/node.rs
+++ b/src/node.rs
@ -50,12 +50,27 @@ impl<'src> Node<'src> for Expression<'src> {
  fn tree(&self) -> Tree<'src> {
    match self {
      Expression::Concatination { lhs, rhs } => Tree::atom("+").push(lhs.tree()).push(rhs.tree()),
-      Expression::Call {
-        function,
-        arguments,
-      } => Tree::atom("call")
-        .push(function.lexeme())
-        .extend(arguments.iter().map(|argument| argument.tree())),
+      Expression::Call { thunk } => {
+        let mut tree = Tree::atom("call");
+
+        use Thunk::*;
+        match thunk {
+          Nullary { name, .. } => tree.push_mut(name.lexeme()),
+          Unary { name, arg, .. } => {
+            tree.push_mut(name.lexeme());
+            tree.push_mut(arg.tree());
+          }
+          Binary {
+            name, args: [a, b], ..
+          } => {
+            tree.push_mut(name.lexeme());
+            tree.push_mut(a.tree());
+            tree.push_mut(b.tree());
+          }
+        }
+
+        tree
+      }
      Expression::Variable { name } => Tree::atom(name.lexeme()),
      Expression::StringLiteral {
        string_literal: StringLiteral { cooked, .. },
--- a/src/parser.rs
+++ b/src/parser.rs
@ -379,8 +379,7 @@ impl<'tokens, 'src> Parser<'tokens, 'src> {
        if self.next_is(ParenL) {
          let arguments = self.parse_sequence()?;
          Ok(Expression::Call {
-            function: name,
-            arguments,
+            thunk: Thunk::resolve(name, arguments)?,
          })
        } else {
          Ok(Expression::Variable { name })
@ -837,20 +836,20 @@ mod tests {

  test! {
    name: call_one_arg,
-    text: "x := foo(y)",
-    tree: (justfile (assignment x (call foo y))),
+    text: "x := env_var(y)",
+    tree: (justfile (assignment x (call env_var y))),
  }

  test! {
    name: call_multiple_args,
-    text: "x := foo(y, z)",
-    tree: (justfile (assignment x (call foo y z))),
+    text: "x := env_var_or_default(y, z)",
+    tree: (justfile (assignment x (call env_var_or_default y z))),
  }

  test! {
    name: call_trailing_comma,
-    text: "x := foo(y,)",
-    tree: (justfile (assignment x (call foo y))),
+    text: "x := env_var(y,)",
+    tree: (justfile (assignment x (call env_var y))),
  }

  test! {
@ -1718,4 +1717,76 @@ mod tests {
      setting: "shall",
    },
  }
+
+  error! {
+    name:   unknown_function,
+    input:  "a = foo()",
+    offset: 4,
+    line:   0,
+    column: 4,
+    width:  3,
+    kind:   UnknownFunction{function: "foo"},
+  }
+
+  error! {
+    name:   unknown_function_in_interpolation,
+    input:  "a:\n echo {{bar()}}",
+    offset: 11,
+    line:   1,
+    column: 8,
+    width:  3,
+    kind:   UnknownFunction{function: "bar"},
+  }
+
+  error! {
+    name:   unknown_function_in_default,
+    input:  "a f=baz():",
+    offset: 4,
+    line:   0,
+    column: 4,
+    width:  3,
+    kind:   UnknownFunction{function: "baz"},
+  }
+
+  error! {
+    name: function_argument_count_nullary,
+    input: "x := arch('foo')",
+    offset: 5,
+    line: 0,
+    column: 5,
+    width: 4,
+    kind: FunctionArgumentCountMismatch {
+      function: "arch",
+      found: 1,
+      expected: 0,
+    },
+  }
+
+  error! {
+    name: function_argument_count_unary,
+    input: "x := env_var()",
+    offset: 5,
+    line: 0,
+    column: 5,
+    width: 7,
+    kind: FunctionArgumentCountMismatch {
+      function: "env_var",
+      found: 0,
+      expected: 1,
+    },
+  }
+
+  error! {
+    name: function_argument_count_binary,
+    input: "x := env_var_or_default('foo')",
+    offset: 5,
+    line: 0,
+    column: 5,
+    width: 18,
+    kind: FunctionArgumentCountMismatch {
+      function: "env_var_or_default",
+      found: 1,
+      expected: 2,
+    },
+  }
 }
--- a/src/recipe_resolver.rs
+++ b/src/recipe_resolver.rs
@ -26,9 +26,6 @@ impl<'a, 'b> RecipeResolver<'a, 'b> {
    for recipe in resolver.resolved_recipes.values() {
      for parameter in &recipe.parameters {
        if let Some(expression) = &parameter.default {
-          for (function, argc) in expression.functions() {
-            Function::resolve(&function, argc)?;
-          }
          for variable in expression.variables() {
            resolver.resolve_variable(&variable, &[])?;
          }
@ -38,9 +35,6 @@ impl<'a, 'b> RecipeResolver<'a, 'b> {
      for line in &recipe.body {
        for fragment in &line.fragments {
          if let Fragment::Interpolation { expression, .. } = fragment {
-            for (function, argc) in expression.functions() {
-              Function::resolve(&function, argc)?;
-            }
            for variable in expression.variables() {
              resolver.resolve_variable(&variable, &recipe.parameters)?;
            }
@ -186,26 +180,6 @@ mod tests {
    kind:   UndefinedVariable{variable: "lol"},
  }

-  analysis_error! {
-    name:   unknown_function_in_interpolation,
-    input:  "a:\n echo {{bar()}}",
-    offset: 11,
-    line:   1,
-    column: 8,
-    width:  3,
-    kind:   UnknownFunction{function: "bar"},
-  }
-
-  analysis_error! {
-    name:   unknown_function_in_default,
-    input:  "a f=baz():",
-    offset: 4,
-    line:   0,
-    column: 4,
-    width:  3,
-    kind:   UnknownFunction{function: "baz"},
-  }
-
  analysis_error! {
    name:   unknown_variable_in_default,
    input:  "a f=foo:",
--- a/src/thunk.rs
+++ b/src/thunk.rs
@ -0,0 +1,77 @@
+use crate::common::*;
+
+#[derive(Derivative)]
+#[derivative(Debug, PartialEq = "feature_allow_slow_enum")]
+pub(crate) enum Thunk<'src> {
+  Nullary {
+    name: Name<'src>,
+    #[derivative(Debug = "ignore", PartialEq = "ignore")]
+    function: fn(&FunctionContext) -> Result<String, String>,
+  },
+  Unary {
+    name: Name<'src>,
+    #[derivative(Debug = "ignore", PartialEq = "ignore")]
+    function: fn(&FunctionContext, &str) -> Result<String, String>,
+    arg: Box<Expression<'src>>,
+  },
+  Binary {
+    name: Name<'src>,
+    #[derivative(Debug = "ignore", PartialEq = "ignore")]
+    function: fn(&FunctionContext, &str, &str) -> Result<String, String>,
+    args: [Box<Expression<'src>>; 2],
+  },
+}
+
+impl<'src> Thunk<'src> {
+  pub(crate) fn resolve(
+    name: Name<'src>,
+    mut arguments: Vec<Expression<'src>>,
+  ) -> CompilationResult<'src, Thunk<'src>> {
+    if let Some(function) = crate::function::TABLE.get(&name.lexeme()) {
+      match (function, arguments.len()) {
+        (Function::Nullary(function), 0) => Ok(Thunk::Nullary {
+          function: *function,
+          name,
+        }),
+        (Function::Unary(function), 1) => Ok(Thunk::Unary {
+          function: *function,
+          arg: Box::new(arguments.pop().unwrap()),
+          name,
+        }),
+        (Function::Binary(function), 2) => {
+          let b = Box::new(arguments.pop().unwrap());
+          let a = Box::new(arguments.pop().unwrap());
+          Ok(Thunk::Binary {
+            function: *function,
+            args: [a, b],
+            name,
+          })
+        }
+        _ => Err(
+          name.error(CompilationErrorKind::FunctionArgumentCountMismatch {
+            function: name.lexeme(),
+            found: arguments.len(),
+            expected: function.argc(),
+          }),
+        ),
+      }
+    } else {
+      Err(name.error(CompilationErrorKind::UnknownFunction {
+        function: name.lexeme(),
+      }))
+    }
+  }
+}
+
+impl Display for Thunk<'_> {
+  fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+    use Thunk::*;
+    match self {
+      Nullary { name, .. } => write!(f, "{}()", name.lexeme()),
+      Unary { name, arg, .. } => write!(f, "{}({})", name.lexeme(), arg),
+      Binary {
+        name, args: [a, b], ..
+      } => write!(f, "{}({}, {})", name.lexeme(), a, b),
+    }
+  }
+}