McCarthy's original notation used bracketed "M-expressions" that would be translated into S-expressions. As an example, the M-expression is equivalent to the S-expression . Once Lisp was implemented, programmers rapidly chose to use S-expressions, and M-expressions were abandoned. M-expressions surfaced again with short-lived attempts of MLisp by Horace Enea and CGOL by Vaughan Pratt.
mccarthY'S origInaL nOTaTioN Used bRACKeTed "m-exPRessions" ThAt WoulD be TranSlAted into S-exprESSioNS. As an examPle, The m-EXpressioN is equivAlent to The s-ExpRESsion . oncE liSp was impLEMEnted, PRogRammers rApidly choSe To use s-eXpresSiOns, and m-EXpressiONs WERE abANdoNEd. M-eXpREssIons sUrfaced AgaIN With sHort-lIved attEmPts of MlIsP by hOrACe Enea AnD CgOl BY vaughan praTT.