Accept but ignore "declare function"

src/transpiler/index.ts

@@ -19,6 +19,7 @@ const {
   ImportNamespaceSpecifier,
   Literal,
   Program,
+  TSDeclareFunction,
   TSTypeAliasDeclaration,
   TSInterfaceDeclaration,
 } = AST_NODE_TYPES
@@ -69,12 +70,13 @@ function parseTopLevelStatement(node: any): SubworkflowAST[] {
 
     case TSInterfaceDeclaration:
     case TSTypeAliasDeclaration:
-      // Ignore "type" and "interface" declarations at the top-level
+    case TSDeclareFunction:
+      // Ignore "type", "interface" and "declare function" at the top-level
       return []
 
     default:
       throw new WorkflowSyntaxError(
-        `Only function declarations, imports and type aliases allowed at the top level, encountered ${node?.type}`,
+        `Only function definitions, imports and type aliases allowed at the top level, encountered ${node?.type}`,
         node?.loc,
       )
   }

src/transpiler/statements.ts

@@ -67,6 +67,7 @@ const {
   SwitchStatement,
   ThrowStatement,
   TryStatement,
+  TSDeclareFunction,
   TSTypeAliasDeclaration,
   TSInterfaceDeclaration,
   VariableDeclaration,
@@ -155,7 +156,8 @@ function parseStep(node: any, ctx: ParsingContext): WorkflowStepAST[] {
 
     case TSInterfaceDeclaration:
     case TSTypeAliasDeclaration:
-      // Ignore "type" and "interface" declarations
+    case TSDeclareFunction:
+      // Ignore "type", "interface" and "declare function"
       return []
 
     default:

test/transpiler.spec.ts

@@ -69,6 +69,26 @@ describe('Type annotations', () => {
 
     expect(observed).to.deep.equal(expected)
   })
+
+  it('ignores interface declaration', () => {
+    const code = `
+    interface Person {
+      name: string
+    }`
+    const observed = YAML.parse(transpile(code)) as unknown
+
+    expect(observed).to.deep.equal({})
+  })
+
+  it('ignores type declaration', () => {
+    const code = `
+    type Person = {
+      name: string
+    }`
+    const observed = YAML.parse(transpile(code)) as unknown
+
+    expect(observed).to.deep.equal({})
+  })
 })
 
 describe('Function definition', () => {
@@ -116,6 +136,17 @@ describe('Function definition', () => {
     expect(observed).to.deep.equal(expected)
   })
 
+  it('ignores function declaration', () => {
+    const code = `
+    declare function computeIt()
+    export declare function exportedComputation()
+    `
+
+    const observed = YAML.parse(transpile(code)) as unknown
+
+    expect(observed).to.deep.equal({})
+  })
+
   it('throws if function is defined in a nested scope', () => {
     const code = `
     function main() {