SYNTAX ERROR

A SYNTAX ERROR is an error message which indicates that a rule of APL syntax was violated. A SYNTAX ERROR may indicate an ill-formed expression which violates APL's grammar: However, a SYNTAX ERROR may also indicate a problem not with the sequence of tokens in a statement, but with their meaning. For example, below an error results when a function is called with invalid valence: here, a monadic function with two arguments. Depending on the value of, the same statement may or may not be considered invalid syntax. This is to be expected, since APL does not have a context-free grammar and needs to know the type of each variable to parse a statement.