Test-Driven Language Development with Spoofax

This short primer shows how to use tests as a basis for language development with Spoofax. As an example project we create a small 'calculator' language that shows many of the basics of language definitions.

The source for our example project is collected in before.zip^?. The complete project, with all functionality implemented to make the test cases succeed is collected in after.zip^?.

A Calculator Language

Language definition tests

spt file

basic form

quote with [[ or [[[ or [[[[

Syntax

test Add [[
  1 + 2
]] parse succeeds

test Multiply [[
  1 * 2
]]

test Abstract syntax (1) [[
  1
]]
  parse to Int("1")

test Abstract syntax (2) [[
  1 * 2
]]
  parse to Mul(Int("1"), Int("2"))

test Parentheses [[
  (1 + 2)
]]

"(" Expr ")" -> Expr {bracket}

test Parentheses in abstract syntax [[
  (1 + 2)
]] parse to Plus(_, _)

test Multiply and add (1) [[
  1 + 2 * 3
]] parse to Add(_, Mul(_, _))

test Multiply and add (2) [[
  1 + 2 * 3
]] parse to [[
  1 + (2 * 3)
]]

test Add and multiply [[
  1 * 2 + 3
]] parse to [[
  (1 * 2) + 3
]]

test Add and add [[
  1 + 2 + 3
]] parse to [[
  (1 + 2) + 3
]]

Evaluation of expressions

Base case:

test Constant [[
  1
]] run calc to "1"

evaluate.str:

  calc:
    Int(i) -> i

Operator:

test Add [[
  1 + 1
]] run calc to "2"

evaluate.str:

  calc:
    Plus(x, y) -> <addS> (<calc> x, <calc> y)

test Multiply [[
  2 * 2
]] run calc to "4"

test Multiply and add [[
  2 * 2 + 1
]] run calc to "5"

test Multiply and add (2) [[
  2 * (2 + 1)
]] run calc to "6"

Variables

test Variable [[
  x
]] parse

test Variable [[
  longname
]] parse

Calculang.sdf:

    ID         -> Exp {cons("Var")}

assignment statements

test Assignment [[
  x = 4
]] parse

    Stm        -> Start {cons("Statements")}
    ID "=" Exp -> Stm {cons("Assign")}
    Exp        -> Stm

test Multiple statements [[
   x = 1
   y = 2
]] parse to Statements([Assign(_, _), Assign(_, _)])

    Stm*       -> Start {cons("Statements")}
    ID "=" Exp -> Stm {cons("Assign")}
    Exp        -> Stm
    ID         -> Exp {cons("Var")}

regression in syntax.spt!?

add {prefer} attribute to CalcuLang.sdf

    Exp -> Start {prefer}

what I want eventually:

test Eval variable [[
  x = 4
  x
]] run calc to "4"

but first:

test Evaluate multiple statements [[
  1
  2
]] run calc to "2"

  calc:
     Statements(s*) -> last
     where
        s'*  := <map(calc)> s*;
        last := <last> s'*

test Eval constant [[
  PI
]] run calc to "3.14"

  calc:
    Var("PI") -> "3.14"

revisit:

test Eval variable [[
  x = 4
  x
]] run calc to "4"

  calc:
    Assign(x, v) -> v'
    where
      v' := <calc> v;
      rules(
        GetValue: x -> v'
      )

  calc:
    Var(v) -> <GetValue> v

test Eval multiple variables [[
  x = 2
  y = x * 2 + x
  y
]] run calc to "6"

t4-editor.spt

test Variable unassigned [[
  y
]] 1 error /unassigned/

  analyze =
    topdown(try(record-var))

  record-var:
    Assign(x, e) -> Assign(x, e)
    with
      rules(
        GetVar :+ x -> x
      )
  
  constraint-error:
    Var(v) -> (v, $[Unassigned variable])
    where
      not(<GetVar> v)

test Multiple assignments to same variable [[
  y = 1
  y = 2
  y
]] /multiple/

  constraint-error:
    Var(v) -> (v, $[Multiple assignments to same variable])
    where
      all-vs := <bagof-GetVar> v;
      <gt> (<length> all-vs, 1)

test Reference resolving (1) [[
  x = 4
  [[x]]
]] resolve

test Reference resolving (2) [[
  [[x]] = 4
  [[x]]
]] resolve #2 to #1

test Content completion [[
  avariable = 1
  [[a]]
]] complete to "avariable"

t5-compilation.spt

test Constant [[
  1
]] build generate-java "
      public class Output {
        public static void main(String[] args) {
          System.out.println(1);
          System.exit(0);
        }
      }"

test Constant [[
  1 + 2
]] build generate-java 

  to-java:
    _ -> $<
      public class Output {
        public static void main(String[] args) {
          System.out.println(42);
          System.exit(0);
        }
      }
    >

t6-execution.spt

test 42 [[
  42
]] build generate-result to 42

test 42, part deux [[
  41 + 1
]] build generate-result to 42
...variables, etc....
...add to evaluation tests??...

t7-refactoring

test Basic rename [[
  a = 1
  [[a]]
]] refactor rename-var("b") to [[
  b = 1
  b
]]

test Another rename [[
  a = 1
  b = 2
  [[a]]
]] refactor rename-var("c") to [[
  c = 1
  b = 2
  c
]]

test Rename collission [[
  a = 1
  b = 1
  [[a]]
]] refactor rename-var("b") to _
   1 error

  rename-var:
    (newname, selected-name, position, ast, path, project-path) -> ([(ast, new-ast)], fatal-errors, errors, warnings)
    with
      new-ast  := <topdown(try(rename-type(|selected-name, newname)))> ast; 
      (errors, warnings) := <semantic-constraint-issues> (ast, new-ast);
      fatal-errors := []

  rename-type(|old-name, new-name):
    Assign(old-name, y) -> Assign(new-name, y)

  rename-type(|old-name, new-name):
    Var(old-name) -> Var(new-name)
    
  semantic-constraint-issues:
    (ast, new-ast) -> (<diff>(new-errors, errors), <diff>(new-warnings, warnings))
    where
      (_, errors, warnings, _) := <editor-analyze> (ast, "", "");
      (_, new-errors, new-warnings, _) := <editor-analyze> (new-ast, "", "")

t8-shell

test Arithmetic API
  <mul> (2, 3) => 6

test String-based arithmetic API
  <mulS> ("2", "3") => "6"

test Foo 
  let
    foo = !4
  in
    foo;
    debug
  end