program     := term ';' program
             | declaration ';' program
declaration := func strictident+ '=' term ';'
term        := appterm term
             | appterm
appterm     := func
             | ident
             | '\' strictident+ '.' term
             | '(' term ')'
strictident := '!'? ident
func        := 'A' | 'B' | ... | 'Z'
ident       := 'a' | 'b' | ... | 'z'