if

Table of Contents

• When to use if vs when
• No else, no else if
• No when on if
• ask inside if
• Scoping
• See also

if <condition>
  ... statements ...
end

Runs the body block when <condition> evaluates to true. The condition uses the same expression grammar as when. Nested if and repeat, ask, and any action statement may appear inside.

When to use if vs when

if and the per-statement when clause solve the same problem from opposite ends:

• when gates a single statement.
• if gates a block of statements with one shared condition.

If you find yourself writing the same when <cond> on three or more consecutive statements, if is usually clearer:

if use_tests
  mkdir "tests"
  file "tests/README.md" content "# Tests"
  file "tests/test_main.cpp" from "templates/test_main.cpp"
end

versus

mkdir "tests" when use_tests
file "tests/README.md" content "# Tests" when use_tests
file "tests/test_main.cpp" from "templates/test_main.cpp" when use_tests

Both are valid. The if form makes the relationship between the statements visible.

No else, no else if

Spudlang has no else or else if. A multi-branch decision composes from nested if blocks or from per-statement when clauses with mutually-exclusive conditions.

ask language "Language?" string options "python" "rust" "go"
 
if language == "python"
  copy "templates/python" into project
end
if language == "rust"
  copy "templates/rust" into project
end
if language == "go"
  copy "templates/go" into project
end

For two-branch decisions, two if blocks with negated conditions work, but a when on each statement is often more readable.

No when on if

An if block does not itself accept a when clause: the if is the gate. To express "do this block only when `a and b`", put the compound condition on the if:

if use_tests and use_coverage
  mkdir "coverage"
end

Inner statements may still carry their own when, which combines with the outer if:

if use_tests
  mkdir "tests"
  file "tests/coverage.cfg" content "..." when use_coverage
end

ask inside if

An ask lexically inside an if body that has no inner when clause does not need a default. The if is the gate.

ask use_tests "Tests?" bool default false
if use_tests
  ask test_runner "Test runner?" string options "ctest" "gtest" default "ctest"
end

If use_tests is false, the inner ask never prompts. The variable test_runner is not bound in that case.

An ask inside if that also carries its own when clause still needs a default, because the inner gate can be false while the outer if is true.

Scoping

An if body introduces a new scope. let and as declared inside the block are local to it and are not visible after end. The no-shadowing rule applies.

ask use_tests "Tests?" bool default false
if use_tests
  let test_dir = "{dir}/tests"
  mkdir test_dir
end
file test_dir/"main.cpp" content ""    # error: 'test_dir' is out of scope

A path alias bound by as inside an if is conditionally scoped under the if's condition.

See also

• repeat: loop a block; combine with if or when to gate inside the loop.
• Scoping: rules for let, as, and ask inside an if.
• Types and expressions: full grammar for <condition>.