If a==1:

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If a==1: is esoteric programming language, where program ends correctly, if accumulator==1, but if accumulator!=1, program outputs f"ERR: {a}".

Commands

command	description
+	inc
-	dec
.	out

Dont confuse commands with BittyLang

Interpreter in python

a=0
for c in input():
    if c==".":
        print(a)
    if c=="+":
        a+=1
    if c=="-":
        a-=1
if a==1:
    break
if a!=1
    print("ERR:", a)
    break

Examples

XKCD Random Number

++++.

XKCD Random Number without ERR

++++.---