4e: Parsing (Combinators)

+bend

Conditional composer.

Parsing composer: connects the $edge .vex with the subsequent $rule .sab as an optional suffix, using gate .raq to compose or reject its result. If there is no suffix, or if the suffix fails to be composed with the current result, the current result is produced. Used to map a group of $rules to a specified output.

Accepts

.raq is a gate.

.sab is a rule.

.vex is an edge.

Produces

A $rule.

Source

++  bend
  ~/  %bend
  =+  raq=|*([a=* b=*] [~ u=[a b]])
  |@
  ++  $
    ~/  %fun
    |*  [vex=edge sab=rule]
    ?~  q.vex
      vex
    =+  yit=(sab q.u.q.vex)
    =+  yur=(last p.vex p.yit)
    ?~  q.yit
      [p=yur q=q.vex]
    =+  vux=(raq p.u.q.vex p.u.q.yit)
    ?~  vux
      [p=yur q=q.vex]
    [p=yur q=[~ u=[p=u.vux q=q.u.q.yit]]]
  --

Examples

> (;~((bend |=([a=char b=char] ?.(=(a b) ~ (some +(a))))) prn prn) [1 1] "qs")
[p=[p=1 q=3] q=[~ u=[p=113 q=[p=[p=1 q=2] q="s"]]]]

> (;~((bend |=([a=char b=char] ?.(=(a b) ~ (some +(a))))) prn prn) [1 1] "qqq")
[p=[p=1 q=3] q=[~ u=[p=114 q=[p=[p=1 q=3] q="q"]]]]

> `@t`(scan "aa" ;~((bend |=([a=char b=char] ?.(=(a b) ~ (some +(a))))) prn prn))
'b'

> (scan "ba" ;~((bend |=([a=char b=char] ?.(=(a b) ~ (some +(a))))) prn prn))
{1 3}
syntax error

> `(unit @tas)`(scan "" ;~((bend) (easy ~) sym))
~

> `(unit @tas)`(scan "sep" ;~((bend) (easy ~) sym))
[~ %sep]

---

+comp

Arbitrary compose.

Parsing composer: connects the $edge .vex with a following $rule .sab, combining the contents of .vex with the result of .sab using a binary gate .raq. Used to fold over the results of several $rules.

Accepts

.raq is a gate that accepts a cell of two $nouns, .a and .b, and produces a cell of two $nouns.

.vex is an edge.

.sab is a rule.

Produces

A $rule.

Source

++  comp
  ~/  %comp
  =+  raq=|*([a=* b=*] [a b])
  |@
  ++  $
    ~/  %fun
    |*  [vex=edge sab=rule]
    ~!  +<
    ?~  q.vex
      vex
    =+  yit=(sab q.u.q.vex)
    =+  yur=(last p.vex p.yit)
    ?~  q.yit
      [p=yur q=q.yit]
    [p=yur q=[~ u=[p=(raq p.u.q.vex p.u.q.yit) q=q.u.q.yit]]]
  --

Examples

> (scan "123" ;~((comp |=([a=@ud b=@ud] (add a b))) dit dit dit))
6

> (scan "12" ;~((comp |=([a=@ud b=@ud] (add a b))) dit dit dit))
{1 3}
syntax error

---

+fail

Never parse.

Produces an $edge at the same text position ($hair) with a failing result (q=~).

Accepts

.tub is a $nail.

Produces

An $edge.

Source

++  fail  |=(tub=nail [p=p.tub q=~])

Examples

> (fail [[1 1] "abc"])
[p=[p=1 q=1] q=~]

> (fail [[p=1.337 q=70] "Parse me, please?"])
[p=[p=1.337 q=70] q=~]

---

+glue

Skip delimiter.

Parsing composer: connects an $edge .vex with a following $rule .sab by parsing the $rule .bus (the delimiting symbol) and throwing out the result.

Accepts

.bus is a $rule.

.vex is an $edge.

.sab is a $rule.

Produces

A $rule.

Source

++  glue
  ~/  %glue
  |*  bus=rule
  ~/  %fun
  |*  [vex=edge sab=rule]
  (plug vex ;~(pfix bus sab))

Examples

> `[@ud @tas @tas]`(scan "200|mal|bon" ;~((glue bar) dem sym sym))
[200 %mal %bon]

> `[@ud @t @tas]`(scan "200|;|bon" ;~((glue bar) dem mic sym))
[200 ';' %bon]

---

+less

Parse unless.

Parsing composer: if an $edge .vex reflects a success, fail. Otherwise, connect .vex with the following $rule.

Accepts

.vex is an $edge.

.sab is a $rule.

Produces

An $edge.

Source

++  less
  |*  [vex=edge sab=rule]
  ?~  q.vex
    =+  roq=(sab)
    [p=(last p.vex p.roq) q=q.roq]
  (fail +<.sab)

Examples

> (scan "sas-/lo" (star ;~(less lus bar prn)))
"sas-/lo"

> (scan "sas-/l+o" (star ;~(less lus bar prn)))
! {1 8}
! exit

> (scan "sas|-/lo" (star ;~(less lus bar prn)))
! {1 5}
! exit

---

+pfix

Discard first rule.

Parsing composer: connects an $edge .vex with two subsequent $rules, ignoring the result of the first and producing the result of the second.

Accepts

.vex is an $edge.

.sab is a $rule.

Produces

An $edge.

Source

++  pfix
  ~/  %pfix
  |*  sam=[vex=edge sab=rule]
  %.  sam
  (comp |*([a=* b=*] b))

Examples

> `@t`(scan "%him" ;~(pfix cen sym))
'him'

> (scan "+++10" ;~(pfix (star lus) dem))
10

---

+plug

Parse to tuple.

Parsing composer: connects an $edge .vex with a following $rule .sab, producing a cell of both the results. See also: the monad applicator ;~ for a more detailed explanation.

Accepts

.vex is an $edge.

.sab is a $rule.

Produces

An $edge.

Source

++  plug
  ~/  %plug
  |*  [vex=edge sab=rule]
  ?~  q.vex
    vex
  =+  yit=(sab q.u.q.vex)
  =+  yur=(last p.vex p.yit)
  ?~  q.yit
    [p=yur q=q.yit]
  [p=yur q=[~ u=[p=[p.u.q.vex p.u.q.yit] q=q.u.q.yit]]]

Examples

> (scan "1..20" ;~(plug dem dot dot dem))
[1 '.' '.' 20]

---

+pose

Parse options.

Parsing composer: if .vex reflects a failure, connect it with the following $rule .sab. See also: the monad applicator ;~

Accepts

.vex is an $edge.

.sab is a $rule.

Produces

An $edge.

Source

++  pose
  ~/  %pose
  |*  [vex=edge sab=rule]
  ?~  q.vex
    =+  roq=(sab)
    [p=(last p.vex p.roq) q=q.roq]
  vex

Examples

> `@t`(scan "+" ;~(pose lus tar cen))
'+'

> `@t`(scan "*" ;~(pose lus tar cen))
'*'

> `@t`(scan "%" ;~(pose lus tar cen))
'%'

> `@t`(scan "-" ;~(pose lus tar cen))
! {1 1}
! exit

---

+sfix

Discard second rule.

Parsing composer: connects $edge .vex with two subsequent $rules returning the result of the first and discarding the result of the second.

Accepts

.vex is an $edge.

.sab is a $rule.

Produces

An $edge.

Source

++  sfix
  ~/  %sfix
  |*  sam=[vex=edge sab=rule]
  %.  sam
  (comp |*([a=* b=*] a))

Examples

> `@t`(scan "him%" ;~(sfix sym cen))
'him'

> (scan "10+++" ;~(sfix dem (star lus)))
q=10

---

+simu

First and second.

Parsing composer: if an $edge .vex reflects a failure, fail. Otherwise, connect .vex with the following $rule.

Accepts

.vex is an $edge.

.sab is a $rule.

Produces

An $edge.

Source

++  simu
  |*  [vex=edge sab=rule]
  ?~  q.vex
    vex
  =+  roq=(sab)
  roq

Examples

> (scan "~zod" scat:vast)
[%dtzy p=%p q=0]

> (scan "%zod" scat:vast)
[%dtzz p=%tas q=6.582.138]

> (scan "%zod" ;~(simu cen scat:vast))
[%dtzz p=%tas q=6.582.138]

> (scan "~zod" ;~(simu cen scat:vast))
! {1 1}
! exit

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