diff options
Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 95 |
1 files changed, 93 insertions, 2 deletions
@@ -12559,9 +12559,10 @@ allowing the operator to be used to terminate at any point. -.coNP Operator @ block +.coNP Operators @ block and @ block* .synb .mets (block < name << body-form *) +.mets (block* < name-form << body-form *) .syne .desc The @@ -12577,6 +12578,15 @@ and A block named by the symbol nil is slightly special: it is understood to be an anonymous block. +The +.code block* +operator differs from +.code block +in that it evaluates +.metn name-form , +which is expected to produce a symbol. The resulting symbol +is used for the name of the block. + A named or anonymous block establishes an exit point for the .code return-from or @@ -12610,6 +12620,11 @@ block does not lexically surround .codn foo . +It is because blocks are dynamic that the +.code block* +variant exists; for lexically scoped blocks, it would make little +sense to have support a dynamically computed name. + Thus blocks in \*(TL provide dynamic non-local returns, as well as returns out of lexical nesting. @@ -12633,7 +12648,21 @@ is not allowed in Common Lisp, but can be transliterated to: Note that foo is quoted in CL. This underscores the dynamic nature of the construct. .code throw -itself is a function and not an operator. +itself is a function and not an operator. Also note that the CL +example, in turn, is even more closely transcribed back into \*(TL +simply by replacing its +.code throw +and +.code catch +with +.code return* +and +.code block* : + +.cblk + (defun func () (return* 'foo 42)) + (block* 'foo (func)) +.cble Common Lisp blocks also do not support delimited continuations. @@ -12685,6 +12714,37 @@ terminates block .codn foo , and so the second pprint form is not evaluated. +.coNP Function @ return* +.synb +.mets (return* < name <> [ value ]) +.syne +.desc +The +.code return* +function is similar to the the +.code return-from +operator, except that +.code name +is an ordinary function parameter, and so when +.code return* +is used, an argument expression must be specified which evaluates +to a symbol. Thus +.code return* +allows the target block of a return to be dynamically computed. + +The following equivalence holds between the operator and function: + +.cblk + (return-from a b) <--> (return* 'a b) +.cble + +Expressions used as +.meta name +arguments to +.code return* +which do not simply quote a symbol have no equivalent in +.codn return-from . + .SS* Evaluation .coNP Function @ eval @@ -27724,6 +27784,37 @@ operators to escape out of a block in which a continuation has been captured. Neglecting to unwind is valid due to the expectation that control will return into a restarted copy of that context. +.coNP Function @ sys:abscond* +.synb +.mets (sys:abscond* < name <> [ value ]) +.syne +.desc +The +.code sys:return* +function is similar to the the +.code sys:abscond-from +operator, except that +.code name +is an ordinary function parameter, and so when +.code return* +is used, an argument expression must be specified which evaluates +to a symbol. Thus +.code sys:abscond* +allows the target block of a return to be dynamically computed. + +The following equivalence holds between the operator and function: + +.cblk + (sys:abscond-from a b) <--> (sys:abscond* 'a b) +.cble + +Expressions used as +.meta name +arguments to +.code abscond* +which do not simply quote a symbol have no equivalent in +.codn abscond-from . + .coNP Macros @ obtain and @ yield-from .synb .mets (obtain << forms *) |