check whether it should merge the top operator when the next operator is `op`

(try to) extract a function signature (like "f[x, y]") from the given Expression used in assignment classification (variable assignment or function de

(try to) extract an identifier from the given Expression used in assignment classification (variable assignment or function declaration)

fold ')'

fold ']' to '[', return the arguments list

pop a value from stack with empty check

trim leading zero elements

initialize an FFT context with maximum length `m`

initialize an FFT context with minimum length `m`