#Dyalog APL, 1 byte

⍳

This has worked since the very first APL, back in the seventies:

⍳⎕

No built-in (also always worked):

+\⎕⍴1

Cumulative sum +\ of input ⎕ number of ⍴ 1s.

Obviously you will need enough memory to contain the result. Here is a print loop to avoid memory full:

{⎕←1+⍵}⍣⎕⊢0

{return and print ⎕← 1+ argument ⍵ } applied ⍣ input ⎕ times to ⊢ 0.

Dyalog APL, 1 byte

⍳

This has worked since the very first APL, back in the seventies:

⍳⎕

No built-in (also always worked):

+\⎕⍴1

Cumulative sum +\ of input ⎕ number of ⍴ 1s.

Obviously you will need enough memory to contain the result. Here is a print loop to avoid memory full:

{⎕←1+⍵}⍣⎕⊢0

{return and print ⎕← 1+ argument ⍵ } applied ⍣ input ⎕ times to ⊢ 0.

Dyalog APL, 1 byte

⍳

This has worked since the very first APL, back in the seventies:

⍳⎕

No built-in (also always worked):

+\⎕⍴1

Cumulative sum +\ of input ⎕ number of ⍴ 1s.

Obviously you will need enough memory to contain the result. Here is a print loop to avoid memory full:

{⎕←1+⍵}⍣⎕⊢0

{return and print ⎕← 1+ argument ⍵ } applied ⍣ input ⎕ times to ⊢ 0.

#Dyalog APL, 1 byte

⍳

This has worked since the very first APL, back in the seventies:

⍳⎕

No built-in (also always worked):

+\⎕⍴1

Cumulative sum +\ of input ⎕ number of ⍴ 1s.

Obviously you will need enough memory to contain the result. Here is a print loop to avoid memory full:

{⎕←1+⍵}⍣⎕⊢0

{return and print ⎕← 1+ argument ⍵ } applied ⍣ input ⎕ times to ⊢ 0.