my dueling links, above, prolly confused some, so here is an excerpt regarding dast:

Quote:

It seemed uniquely appropriate to check for information about this particular word in the Dictionary of American Regional English (known commonly and affectionately as "DARE"), where their attestations list several indicative, nonnegative, uncontracted forms of dare that are relevant for us. These include darst, dast, darse, dass, and das. The last two, used before an infinitive, are said to "have evidently lost the final -t by assimilation to the following to. Thus DARE's citations include both "Don't reckon we dast venture into them mountains till it's over" (Moody, 1956) and "Solomon didn' das' ter let on 'bout w'at he 'spicioned" (Chessnut, Conjure Woman, 1899). The DARE editors postulate that these positive forms probably represent a "back-formation from the negative da(r)sn't."



ip, you can read the whole enchilada by clicking on but in my previous.